File ssl.h

SSL/TLS functions.

SECTION: Module configuration options

This section allows for the setting of module specific sizes and configuration options. The default values are already present in the relevant header files and should suffice for the regular use cases.

Our advice is to enable options and change their values here only if you have a good reason and know the consequences.

MBEDTLS_TLS_EXT_CID

At the time of writing, the CID extension has not been assigned its final value. Set this configuration option to make Mbed TLS use a different value.

A future minor revision of Mbed TLS may change the default value of this option to match evolving standards and usage.

SECTION: Module settings

The configuration options you can set for this module are in this section. Either change them in config.h or define them on the compiler command line.

MBEDTLS_SSL_DEFAULT_TICKET_LIFETIME: Lifetime of session tickets (if enabled)

MBEDTLS_SSL_MAX_CONTENT_LEN

Maximum length (in bytes) of incoming and outgoing plaintext fragments.

This determines the size of both the incoming and outgoing TLS I/O buffers in such a way that both are capable of holding the specified amount of plaintext data, regardless of the protection mechanism used.

To configure incoming and outgoing I/O buffers separately, use MBEDTLS_SSL_IN_CONTENT_LEN and MBEDTLS_SSL_OUT_CONTENT_LEN, which overwrite the value set by this option.

Uncomment to set the maximum plaintext size of both incoming and outgoing I/O buffers.

Size of the input / output buffer

Note

When using a value less than the default of 16KB on the client, it is recommended to use the Maximum Fragment Length (MFL) extension to inform the server about this limitation. On the server, there is no supported, standardized way of informing the client about restriction on the maximum size of incoming messages, and unless the limitation has been communicated by other means, it is recommended to only change the outgoing buffer size MBEDTLS_SSL_OUT_CONTENT_LEN while keeping the default value of 16KB for the incoming buffer.

MBEDTLS_SSL_IN_CONTENT_LEN

Maximum length (in bytes) of incoming plaintext fragments.

This determines the size of the incoming TLS I/O buffer in such a way that it is capable of holding the specified amount of plaintext data, regardless of the protection mechanism used.

If this option is undefined, it inherits its value from MBEDTLS_SSL_MAX_CONTENT_LEN.

Uncomment to set the maximum plaintext size of the incoming I/O buffer independently of the outgoing I/O buffer.

Note

When using a value less than the default of 16KB on the client, it is recommended to use the Maximum Fragment Length (MFL) extension to inform the server about this limitation. On the server, there is no supported, standardized way of informing the client about restriction on the maximum size of incoming messages, and unless the limitation has been communicated by other means, it is recommended to only change the outgoing buffer size MBEDTLS_SSL_OUT_CONTENT_LEN while keeping the default value of 16KB for the incoming buffer.

MBEDTLS_SSL_OUT_CONTENT_LEN

Maximum length (in bytes) of outgoing plaintext fragments.

This determines the size of the outgoing TLS I/O buffer in such a way that it is capable of holding the specified amount of plaintext data, regardless of the protection mechanism used.

If this option undefined, it inherits its value from MBEDTLS_SSL_MAX_CONTENT_LEN.

It is possible to save RAM by setting a smaller outward buffer, while keeping the default inward 16384 byte buffer to conform to the TLS specification.

The minimum required outward buffer size is determined by the handshake protocol’s usage. Handshaking will fail if the outward buffer is too small. The specific size requirement depends on the configured ciphers and any certificate data which is sent during the handshake.

Uncomment to set the maximum plaintext size of the outgoing I/O buffer independently of the incoming I/O buffer.

MBEDTLS_SSL_DTLS_MAX_BUFFERING

Maximum number of heap-allocated bytes for the purpose of DTLS handshake message reassembly and future message buffering.

This should be at least 9/8 * MBEDTLS_SSL_IN_CONTENT_LEN to account for a reassembled handshake message of maximum size, together with its reassembly bitmap.

A value of 2 * MBEDTLS_SSL_IN_CONTENT_LEN (32768 by default) should be sufficient for all practical situations as it allows to reassembly a large handshake message (such as a certificate) while buffering multiple smaller handshake messages.

MBEDTLS_SSL_CID_IN_LEN_MAX: The maximum length of CIDs used for incoming DTLS messages.

MBEDTLS_SSL_CID_OUT_LEN_MAX: The maximum length of CIDs used for outgoing DTLS messages.

MBEDTLS_SSL_CID_PADDING_GRANULARITY

This option controls the use of record plaintext padding when using the Connection ID extension in DTLS 1.2.

The padding will always be chosen so that the length of the padded plaintext is a multiple of the value of this option.

Note: A value of 1 means that no padding will be used for outgoing records.

Note: On systems lacking division instructions, a power of two should be preferred.

MBEDTLS_SSL_TLS1_3_PADDING_GRANULARITY

This option controls the use of record plaintext padding in TLS 1.3.

The padding will always be chosen so that the length of the padded plaintext is a multiple of the value of this option.

Note: A value of 1 means that no padding will be used for outgoing records.

Note: On systems lacking division instructions, a power of two should be preferred.

Defines

MBEDTLS_ERR_SSL_FEATURE_UNAVAILABLE: The requested feature is not available.

MBEDTLS_ERR_SSL_BAD_INPUT_DATA: Bad input parameters to function.

MBEDTLS_ERR_SSL_INVALID_MAC: Verification of the message MAC failed.

MBEDTLS_ERR_SSL_INVALID_RECORD: An invalid SSL record was received.

MBEDTLS_ERR_SSL_CONN_EOF: The connection indicated an EOF.

MBEDTLS_ERR_SSL_UNKNOWN_CIPHER: An unknown cipher was received.

MBEDTLS_ERR_SSL_NO_CIPHER_CHOSEN: The server has no ciphersuites in common with the client.

MBEDTLS_ERR_SSL_NO_RNG: No RNG was provided to the SSL module.

MBEDTLS_ERR_SSL_NO_CLIENT_CERTIFICATE: No client certification received from the client, but required by the authentication mode.

MBEDTLS_ERR_SSL_CERTIFICATE_TOO_LARGE: Our own certificate(s) is/are too large to send in an SSL message.

MBEDTLS_ERR_SSL_CERTIFICATE_REQUIRED: The own certificate is not set, but needed by the server.

MBEDTLS_ERR_SSL_PRIVATE_KEY_REQUIRED: The own private key or pre-shared key is not set, but needed.

MBEDTLS_ERR_SSL_CA_CHAIN_REQUIRED: No CA Chain is set, but required to operate.

MBEDTLS_ERR_SSL_UNEXPECTED_MESSAGE: An unexpected message was received from our peer.

MBEDTLS_ERR_SSL_FATAL_ALERT_MESSAGE: A fatal alert message was received from our peer.

MBEDTLS_ERR_SSL_PEER_VERIFY_FAILED: Verification of our peer failed.

MBEDTLS_ERR_SSL_PEER_CLOSE_NOTIFY: The peer notified us that the connection is going to be closed.

MBEDTLS_ERR_SSL_BAD_HS_CLIENT_HELLO: Processing of the ClientHello handshake message failed.

MBEDTLS_ERR_SSL_BAD_HS_SERVER_HELLO: Processing of the ServerHello handshake message failed.

MBEDTLS_ERR_SSL_BAD_HS_CERTIFICATE: Processing of the Certificate handshake message failed.

MBEDTLS_ERR_SSL_BAD_HS_CERTIFICATE_REQUEST: Processing of the CertificateRequest handshake message failed.

MBEDTLS_ERR_SSL_BAD_HS_SERVER_KEY_EXCHANGE: Processing of the ServerKeyExchange handshake message failed.

MBEDTLS_ERR_SSL_BAD_HS_SERVER_HELLO_DONE: Processing of the ServerHelloDone handshake message failed.

MBEDTLS_ERR_SSL_BAD_HS_CLIENT_KEY_EXCHANGE: Processing of the ClientKeyExchange handshake message failed.

MBEDTLS_ERR_SSL_BAD_HS_CLIENT_KEY_EXCHANGE_RP: Processing of the ClientKeyExchange handshake message failed in DHM / ECDH Read Public.

MBEDTLS_ERR_SSL_BAD_HS_CLIENT_KEY_EXCHANGE_CS: Processing of the ClientKeyExchange handshake message failed in DHM / ECDH Calculate Secret.

MBEDTLS_ERR_SSL_BAD_HS_CERTIFICATE_VERIFY: Processing of the CertificateVerify handshake message failed.

MBEDTLS_ERR_SSL_BAD_HS_CHANGE_CIPHER_SPEC: Processing of the ChangeCipherSpec handshake message failed.

MBEDTLS_ERR_SSL_BAD_HS_FINISHED: Processing of the Finished handshake message failed.

MBEDTLS_ERR_SSL_ALLOC_FAILED: Memory allocation failed

MBEDTLS_ERR_SSL_HW_ACCEL_FAILED: Hardware acceleration function returned with error

MBEDTLS_ERR_SSL_HW_ACCEL_FALLTHROUGH: Hardware acceleration function skipped / left alone data

MBEDTLS_ERR_SSL_COMPRESSION_FAILED: Processing of the compression / decompression failed

MBEDTLS_ERR_SSL_BAD_HS_PROTOCOL_VERSION: Handshake protocol not within min/max boundaries

MBEDTLS_ERR_SSL_BAD_HS_NEW_SESSION_TICKET: Processing of the NewSessionTicket handshake message failed.

MBEDTLS_ERR_SSL_SESSION_TICKET_EXPIRED: Session ticket has expired.

MBEDTLS_ERR_SSL_PK_TYPE_MISMATCH: Public key type mismatch (eg, asked for RSA key exchange and presented EC key)

MBEDTLS_ERR_SSL_UNKNOWN_IDENTITY: Unknown identity received (eg, PSK identity)

MBEDTLS_ERR_SSL_INTERNAL_ERROR: Internal error (eg, unexpected failure in lower-level module)

MBEDTLS_ERR_SSL_COUNTER_WRAPPING: A counter would wrap (eg, too many messages exchanged).

MBEDTLS_ERR_SSL_WAITING_SERVER_HELLO_RENEGO: Unexpected message at ServerHello in renegotiation.

MBEDTLS_ERR_SSL_HELLO_VERIFY_REQUIRED: DTLS client must retry for hello verification

MBEDTLS_ERR_SSL_BUFFER_TOO_SMALL: A buffer is too small to receive or write a message

MBEDTLS_ERR_SSL_NO_USABLE_CIPHERSUITE: None of the common ciphersuites is usable (eg, no suitable certificate, see debug messages).

MBEDTLS_ERR_SSL_WANT_READ: No data of requested type currently available on underlying transport.

MBEDTLS_ERR_SSL_WANT_WRITE: Connection requires a write call.

MBEDTLS_ERR_SSL_TIMEOUT: The operation timed out.

MBEDTLS_ERR_SSL_CLIENT_RECONNECT: The client initiated a reconnect from the same port.

MBEDTLS_ERR_SSL_UNEXPECTED_RECORD: Record header looks valid but is not expected.

MBEDTLS_ERR_SSL_NON_FATAL: The alert message received indicates a non-fatal error.

MBEDTLS_ERR_SSL_INVALID_VERIFY_HASH: Couldn’t set the hash for verifying CertificateVerify

MBEDTLS_ERR_SSL_CONTINUE_PROCESSING: Internal-only message signaling that further message-processing should be done

MBEDTLS_ERR_SSL_ASYNC_IN_PROGRESS: The asynchronous operation is not completed yet.

MBEDTLS_ERR_SSL_EARLY_MESSAGE: Internal-only message signaling that a message arrived early.

MBEDTLS_ERR_SSL_UNEXPECTED_CID: An encrypted DTLS-frame with an unexpected CID was received.

MBEDTLS_ERR_SSL_VERSION_MISMATCH: An operation failed due to an unexpected version or configuration.

MBEDTLS_ERR_SSL_CRYPTO_IN_PROGRESS: A cryptographic operation is in progress. Try again later.

MBEDTLS_ERR_SSL_BAD_CONFIG: Invalid value in SSL config

MBEDTLS_ERR_SSL_CACHE_ENTRY_NOT_FOUND: Cache entry not found

MBEDTLS_ERR_SSL_CERTIFICATE_VERIFICATION_WITHOUT_HOSTNAME

Attempt to verify a certificate without an expected hostname. This is usually insecure.

In TLS clients, when a client authenticates a server through its certificate, the client normally checks three things:

the certificate chain must be valid;
the chain must start from a trusted CA;
the certificate must cover the server name that is expected by the client.

Omitting any of these checks is generally insecure, and can allow a malicious server to impersonate a legitimate server.

The third check may be safely skipped in some unusual scenarios, such as networks where eavesdropping is a risk but not active attacks, or a private PKI where the client equally trusts all servers that are accredited by the root CA.

You should call mbedtls_ssl_set_hostname() with the expected server name before starting a TLS handshake on a client (unless the client is set up to only use PSK-based authentication, which does not rely on the host name). If you have determined that server name verification is not required for security in your scenario, call mbedtls_ssl_set_hostname() with NULL as the server name.

This error is raised if all of the following conditions are met:

A TLS client is configured with the authentication mode MBEDTLS_SSL_VERIFY_REQUIRED (default).
Certificate authentication is enabled.
The client does not call mbedtls_ssl_set_hostname().
The configuration option MBEDTLS_SSL_CLI_ALLOW_WEAK_CERTIFICATE_VERIFICATION_WITHOUT_HOSTNAME is not enabled.

MBEDTLS_SSL_MAJOR_VERSION_3

MBEDTLS_SSL_MINOR_VERSION_0: SSL v3.0

MBEDTLS_SSL_MINOR_VERSION_1: TLS v1.0

MBEDTLS_SSL_MINOR_VERSION_2: TLS v1.1

MBEDTLS_SSL_MINOR_VERSION_3: TLS v1.2

MBEDTLS_SSL_MINOR_VERSION_4: TLS v1.3 (experimental)

MBEDTLS_SSL_TRANSPORT_STREAM: TLS

MBEDTLS_SSL_TRANSPORT_DATAGRAM: DTLS

MBEDTLS_SSL_MAX_HOST_NAME_LEN: Maximum host name defined in RFC 1035

MBEDTLS_SSL_MAX_ALPN_NAME_LEN: Maximum size in bytes of a protocol name in alpn ext., RFC 7301

MBEDTLS_SSL_MAX_ALPN_LIST_LEN: Maximum size in bytes of list in alpn ext., RFC 7301

MBEDTLS_SSL_MAX_FRAG_LEN_NONE: don’t use this extension

MBEDTLS_SSL_MAX_FRAG_LEN_512: MaxFragmentLength 2^9

MBEDTLS_SSL_MAX_FRAG_LEN_1024: MaxFragmentLength 2^10

MBEDTLS_SSL_MAX_FRAG_LEN_2048: MaxFragmentLength 2^11

MBEDTLS_SSL_MAX_FRAG_LEN_4096: MaxFragmentLength 2^12

MBEDTLS_SSL_MAX_FRAG_LEN_INVALID: first invalid value

MBEDTLS_SSL_IS_CLIENT

MBEDTLS_SSL_IS_SERVER

MBEDTLS_SSL_IS_NOT_FALLBACK

MBEDTLS_SSL_IS_FALLBACK

MBEDTLS_SSL_EXTENDED_MS_DISABLED

MBEDTLS_SSL_EXTENDED_MS_ENABLED

MBEDTLS_SSL_CID_DISABLED

MBEDTLS_SSL_CID_ENABLED

MBEDTLS_SSL_ETM_DISABLED

MBEDTLS_SSL_ETM_ENABLED

MBEDTLS_SSL_COMPRESS_NULL

MBEDTLS_SSL_COMPRESS_DEFLATE

MBEDTLS_SSL_VERIFY_NONE

MBEDTLS_SSL_VERIFY_OPTIONAL

MBEDTLS_SSL_VERIFY_REQUIRED

MBEDTLS_SSL_VERIFY_UNSET

MBEDTLS_SSL_LEGACY_RENEGOTIATION

MBEDTLS_SSL_SECURE_RENEGOTIATION

MBEDTLS_SSL_RENEGOTIATION_DISABLED

MBEDTLS_SSL_RENEGOTIATION_ENABLED

MBEDTLS_SSL_ANTI_REPLAY_DISABLED

MBEDTLS_SSL_ANTI_REPLAY_ENABLED

MBEDTLS_SSL_RENEGOTIATION_NOT_ENFORCED

MBEDTLS_SSL_RENEGO_MAX_RECORDS_DEFAULT

MBEDTLS_SSL_LEGACY_NO_RENEGOTIATION

MBEDTLS_SSL_LEGACY_ALLOW_RENEGOTIATION

MBEDTLS_SSL_LEGACY_BREAK_HANDSHAKE

MBEDTLS_SSL_TRUNC_HMAC_DISABLED

MBEDTLS_SSL_TRUNC_HMAC_ENABLED

MBEDTLS_SSL_TRUNCATED_HMAC_LEN

MBEDTLS_SSL_SESSION_TICKETS_DISABLED

MBEDTLS_SSL_SESSION_TICKETS_ENABLED

MBEDTLS_SSL_CBC_RECORD_SPLITTING_DISABLED

MBEDTLS_SSL_CBC_RECORD_SPLITTING_ENABLED

MBEDTLS_SSL_ARC4_ENABLED

MBEDTLS_SSL_ARC4_DISABLED

MBEDTLS_SSL_PRESET_DEFAULT

MBEDTLS_SSL_PRESET_SUITEB

MBEDTLS_SSL_CERT_REQ_CA_LIST_ENABLED

MBEDTLS_SSL_CERT_REQ_CA_LIST_DISABLED

MBEDTLS_SSL_DTLS_SRTP_MKI_UNSUPPORTED

MBEDTLS_SSL_DTLS_SRTP_MKI_SUPPORTED

MBEDTLS_SSL_DTLS_TIMEOUT_DFL_MIN

MBEDTLS_SSL_DTLS_TIMEOUT_DFL_MAX

MBEDTLS_SSL_VERIFY_DATA_MAX_LEN

MBEDTLS_SSL_EMPTY_RENEGOTIATION_INFO: renegotiation info ext

MBEDTLS_SSL_FALLBACK_SCSV_VALUE: RFC 7507 section 2

MBEDTLS_SSL_HASH_NONE

MBEDTLS_SSL_HASH_MD5

MBEDTLS_SSL_HASH_SHA1

MBEDTLS_SSL_HASH_SHA224

MBEDTLS_SSL_HASH_SHA256

MBEDTLS_SSL_HASH_SHA384

MBEDTLS_SSL_HASH_SHA512

MBEDTLS_SSL_SIG_ANON

MBEDTLS_SSL_SIG_RSA

MBEDTLS_SSL_SIG_ECDSA

MBEDTLS_SSL_CERT_TYPE_RSA_SIGN

MBEDTLS_SSL_CERT_TYPE_ECDSA_SIGN

MBEDTLS_SSL_MSG_CHANGE_CIPHER_SPEC

MBEDTLS_SSL_MSG_ALERT

MBEDTLS_SSL_MSG_HANDSHAKE

MBEDTLS_SSL_MSG_APPLICATION_DATA

MBEDTLS_SSL_MSG_CID

MBEDTLS_SSL_ALERT_LEVEL_WARNING

MBEDTLS_SSL_ALERT_LEVEL_FATAL

MBEDTLS_SSL_ALERT_MSG_CLOSE_NOTIFY

MBEDTLS_SSL_ALERT_MSG_UNEXPECTED_MESSAGE

MBEDTLS_SSL_ALERT_MSG_BAD_RECORD_MAC

MBEDTLS_SSL_ALERT_MSG_DECRYPTION_FAILED

MBEDTLS_SSL_ALERT_MSG_RECORD_OVERFLOW

MBEDTLS_SSL_ALERT_MSG_DECOMPRESSION_FAILURE

MBEDTLS_SSL_ALERT_MSG_HANDSHAKE_FAILURE

MBEDTLS_SSL_ALERT_MSG_NO_CERT

MBEDTLS_SSL_ALERT_MSG_BAD_CERT

MBEDTLS_SSL_ALERT_MSG_UNSUPPORTED_CERT

MBEDTLS_SSL_ALERT_MSG_CERT_REVOKED

MBEDTLS_SSL_ALERT_MSG_CERT_EXPIRED

MBEDTLS_SSL_ALERT_MSG_CERT_UNKNOWN

MBEDTLS_SSL_ALERT_MSG_ILLEGAL_PARAMETER

MBEDTLS_SSL_ALERT_MSG_UNKNOWN_CA

MBEDTLS_SSL_ALERT_MSG_ACCESS_DENIED

MBEDTLS_SSL_ALERT_MSG_DECODE_ERROR

MBEDTLS_SSL_ALERT_MSG_DECRYPT_ERROR

MBEDTLS_SSL_ALERT_MSG_EXPORT_RESTRICTION

MBEDTLS_SSL_ALERT_MSG_PROTOCOL_VERSION

MBEDTLS_SSL_ALERT_MSG_INSUFFICIENT_SECURITY

MBEDTLS_SSL_ALERT_MSG_INTERNAL_ERROR

MBEDTLS_SSL_ALERT_MSG_INAPROPRIATE_FALLBACK

MBEDTLS_SSL_ALERT_MSG_USER_CANCELED

MBEDTLS_SSL_ALERT_MSG_NO_RENEGOTIATION

MBEDTLS_SSL_ALERT_MSG_UNSUPPORTED_EXT

MBEDTLS_SSL_ALERT_MSG_UNRECOGNIZED_NAME

MBEDTLS_SSL_ALERT_MSG_UNKNOWN_PSK_IDENTITY

MBEDTLS_SSL_ALERT_MSG_NO_APPLICATION_PROTOCOL

MBEDTLS_SSL_HS_HELLO_REQUEST

MBEDTLS_SSL_HS_CLIENT_HELLO

MBEDTLS_SSL_HS_SERVER_HELLO

MBEDTLS_SSL_HS_HELLO_VERIFY_REQUEST

MBEDTLS_SSL_HS_NEW_SESSION_TICKET

MBEDTLS_SSL_HS_CERTIFICATE

MBEDTLS_SSL_HS_SERVER_KEY_EXCHANGE

MBEDTLS_SSL_HS_CERTIFICATE_REQUEST

MBEDTLS_SSL_HS_SERVER_HELLO_DONE

MBEDTLS_SSL_HS_CERTIFICATE_VERIFY

MBEDTLS_SSL_HS_CLIENT_KEY_EXCHANGE

MBEDTLS_SSL_HS_FINISHED

MBEDTLS_TLS_EXT_SERVERNAME

MBEDTLS_TLS_EXT_SERVERNAME_HOSTNAME

MBEDTLS_TLS_EXT_MAX_FRAGMENT_LENGTH

MBEDTLS_TLS_EXT_TRUNCATED_HMAC

MBEDTLS_TLS_EXT_SUPPORTED_ELLIPTIC_CURVES

MBEDTLS_TLS_EXT_SUPPORTED_POINT_FORMATS

MBEDTLS_TLS_EXT_SIG_ALG

MBEDTLS_TLS_EXT_USE_SRTP

MBEDTLS_TLS_EXT_ALPN

MBEDTLS_TLS_EXT_ENCRYPT_THEN_MAC

MBEDTLS_TLS_EXT_EXTENDED_MASTER_SECRET

MBEDTLS_TLS_EXT_SESSION_TICKET

MBEDTLS_TLS_EXT_ECJPAKE_KKPP

MBEDTLS_TLS_EXT_RENEGOTIATION_INFO

MBEDTLS_PSK_MAX_LEN

MBEDTLS_PREMASTER_SIZE

MBEDTLS_TLS_SRTP_MAX_MKI_LENGTH

MBEDTLS_TLS_SRTP_MAX_PROFILE_LIST_LENGTH

MBEDTLS_TLS_SRTP_AES128_CM_HMAC_SHA1_80

MBEDTLS_TLS_SRTP_AES128_CM_HMAC_SHA1_32

MBEDTLS_TLS_SRTP_NULL_HMAC_SHA1_80

MBEDTLS_TLS_SRTP_NULL_HMAC_SHA1_32

MBEDTLS_TLS_SRTP_UNSET

MBEDTLS_SSL_UNEXPECTED_CID_IGNORE

MBEDTLS_SSL_UNEXPECTED_CID_FAIL

Typedefs

typedef int mbedtls_ssl_send_t(void *ctx, const unsigned char *buf, size_t len)

Callback type: send data on the network.

Note

That callback may be either blocking or non-blocking.

Note

The callback is allowed to send fewer bytes than requested. It must always return the number of bytes actually sent.

Param ctx:: Context for the send callback (typically a file descriptor)
Param buf:: Buffer holding the data to send
Param len:: Length of the data to send
Return:: The callback must return the number of bytes sent if any, or a non-zero error code. If performing non-blocking I/O, MBEDTLS_ERR_SSL_WANT_WRITE must be returned when the operation would block.

typedef int mbedtls_ssl_recv_t(void *ctx, unsigned char *buf, size_t len)

Callback type: receive data from the network.

Note

That callback may be either blocking or non-blocking.

Note

The callback may receive fewer bytes than the length of the buffer. It must always return the number of bytes actually received and written to the buffer.

Param ctx:: Context for the receive callback (typically a file descriptor)
Param buf:: Buffer to write the received data to
Param len:: Length of the receive buffer
Return:: If data has been received, the positive number of bytes received.
Return:: 0 if the connection has been closed.
Return:: If performing non-blocking I/O, MBEDTLS_ERR_SSL_WANT_READ must be returned when the operation would block.
Return:: Another negative error code on other kinds of failures.

typedef int mbedtls_ssl_recv_timeout_t(void *ctx, unsigned char *buf, size_t len, uint32_t timeout)

Callback type: receive data from the network, with timeout.

Note

That callback must block until data is received, or the timeout delay expires, or the operation is interrupted by a signal.

Note

The callback may receive fewer bytes than the length of the buffer. It must always return the number of bytes actually received and written to the buffer.

Param ctx:: Context for the receive callback (typically a file descriptor)
Param buf:: Buffer to write the received data to
Param len:: Length of the receive buffer
Param timeout:: Maximum number of milliseconds to wait for data 0 means no timeout (potentially waiting forever)
Return:: The callback must return the number of bytes received, or a non-zero error code: MBEDTLS_ERR_SSL_TIMEOUT if the operation timed out, MBEDTLS_ERR_SSL_WANT_READ if interrupted by a signal.

typedef void mbedtls_ssl_set_timer_t(void *ctx, uint32_t int_ms, uint32_t fin_ms)

Callback type: set a pair of timers/delays to watch.

Note

This callback must at least store the necessary information for the associated mbedtls_ssl_get_timer_t callback to return correct information.

Note

If using an event-driven style of programming, an event must be generated when the final delay is passed. The event must cause a call to mbedtls_ssl_handshake() with the proper SSL context to be scheduled. Care must be taken to ensure that at most one such call happens at a time.

Note

Only one timer at a time must be running. Calling this function while a timer is running must cancel it. Cancelled timers must not generate any event.

Param ctx:: Context pointer
Param int_ms:: Intermediate delay in milliseconds
Param fin_ms:: Final delay in milliseconds 0 cancels the current timer.

typedef int mbedtls_ssl_get_timer_t(void *ctx)

Callback type: get status of timers/delays.

Param ctx:: Context pointer
Return:: This callback must return: -1 if cancelled (fin_ms == 0), 0 if none of the delays have passed, 1 if only the intermediate delay has passed, 2 if the final delay has passed.

typedef struct mbedtls_ssl_session mbedtls_ssl_session

typedef struct mbedtls_ssl_context mbedtls_ssl_context

typedef struct mbedtls_ssl_config mbedtls_ssl_config

typedef struct mbedtls_ssl_transform mbedtls_ssl_transform

typedef struct mbedtls_ssl_handshake_params mbedtls_ssl_handshake_params

typedef struct mbedtls_ssl_sig_hash_set_t mbedtls_ssl_sig_hash_set_t

typedef struct mbedtls_ssl_key_cert mbedtls_ssl_key_cert

typedef struct mbedtls_ssl_flight_item mbedtls_ssl_flight_item

typedef int mbedtls_ssl_async_sign_t(mbedtls_ssl_context *ssl, mbedtls_x509_crt *cert, mbedtls_md_type_t md_alg, const unsigned char *hash, size_t hash_len)

Callback type: start external signature operation.

             This callback is called during an SSL handshake to start
             a signature decryption operation using an
             external processor. The parameter \p cert contains
             the public key; it is up to the callback function to
             determine how to access the associated private key.

             This function typically sends or enqueues a request, and
             does not wait for the operation to complete. This allows
             the handshake step to be non-blocking.

             The parameters \p ssl and \p cert are guaranteed to remain
             valid throughout the handshake. On the other hand, this
             function must save the contents of \p hash if the value
             is needed for later processing, because the \p hash buffer
             is no longer valid after this function returns.

             This function may call mbedtls_ssl_set_async_operation_data()
             to store an operation context for later retrieval
             by the resume or cancel callback.

Note

For RSA signatures, this function must produce output that is consistent with PKCS#1 v1.5 in the same way as mbedtls_rsa_pkcs1_sign(). Before the private key operation, apply the padding steps described in RFC 8017, section 9.2 “EMSA-PKCS1-v1_5” as follows.

If md_alg is MBEDTLS_MD_NONE, apply the PKCS#1 v1.5 encoding, treating hash as the DigestInfo to be padded. In other words, apply EMSA-PKCS1-v1_5 starting from step 3, with T = hash and tLen = hash_len.
If md_alg != MBEDTLS_MD_NONE, apply the PKCS#1 v1.5 encoding, treating hash as the hash to be encoded and padded. In other words, apply EMSA-PKCS1-v1_5 starting from step 2, with digestAlgorithm obtained by calling mbedtls_oid_get_oid_by_md() on md_alg.

Note

For ECDSA signatures, the output format is the DER encoding Ecdsa-Sig-Value defined in RFC 4492 section 5.4.

Param ssl:: The SSL connection instance. It should not be modified other than via mbedtls_ssl_set_async_operation_data().
Param cert:: Certificate containing the public key. In simple cases, this is one of the pointers passed to mbedtls_ssl_conf_own_cert() when configuring the SSL connection. However, if other callbacks are used, this property may not hold. For example, if an SNI callback is registered with mbedtls_ssl_conf_sni(), then this callback determines what certificate is used.
Param md_alg:: Hash algorithm.
Param hash:: Buffer containing the hash. This buffer is no longer valid when the function returns.
Param hash_len:: Size of the hash buffer in bytes.
Return:: 0 if the operation was started successfully and the SSL stack should call the resume callback immediately.
Return:: MBEDTLS_ERR_SSL_ASYNC_IN_PROGRESS if the operation was started successfully and the SSL stack should return immediately without calling the resume callback yet.
Return:: MBEDTLS_ERR_SSL_HW_ACCEL_FALLTHROUGH if the external processor does not support this key. The SSL stack will use the private key object instead.
Return:: Any other error indicates a fatal failure and is propagated up the call chain. The callback should use MBEDTLS_ERR_PK_xxx error codes, and must not use MBEDTLS_ERR_SSL_xxx error codes except as directed in the documentation of this callback.

typedef int mbedtls_ssl_async_decrypt_t(mbedtls_ssl_context *ssl, mbedtls_x509_crt *cert, const unsigned char *input, size_t input_len)

Callback type: start external decryption operation.

             This callback is called during an SSL handshake to start
             an RSA decryption operation using an
             external processor. The parameter \p cert contains
             the public key; it is up to the callback function to
             determine how to access the associated private key.

             This function typically sends or enqueues a request, and
             does not wait for the operation to complete. This allows
             the handshake step to be non-blocking.

             The parameters \p ssl and \p cert are guaranteed to remain
             valid throughout the handshake. On the other hand, this
             function must save the contents of \p input if the value
             is needed for later processing, because the \p input buffer
             is no longer valid after this function returns.

             This function may call mbedtls_ssl_set_async_operation_data()
             to store an operation context for later retrieval
             by the resume or cancel callback.

Warning

RSA decryption as used in TLS is subject to a potential timing side channel attack first discovered by Bleichenbacher in 1998. This attack can be remotely exploitable in practice. To avoid this attack, you must ensure that if the callback performs an RSA decryption, the time it takes to execute and return the result does not depend on whether the RSA decryption succeeded or reported invalid padding.

Param ssl:: The SSL connection instance. It should not be modified other than via mbedtls_ssl_set_async_operation_data().
Param cert:: Certificate containing the public key. In simple cases, this is one of the pointers passed to mbedtls_ssl_conf_own_cert() when configuring the SSL connection. However, if other callbacks are used, this property may not hold. For example, if an SNI callback is registered with mbedtls_ssl_conf_sni(), then this callback determines what certificate is used.
Param input:: Buffer containing the input ciphertext. This buffer is no longer valid when the function returns.
Param input_len:: Size of the input buffer in bytes.
Return:: 0 if the operation was started successfully and the SSL stack should call the resume callback immediately.
Return:: MBEDTLS_ERR_SSL_ASYNC_IN_PROGRESS if the operation was started successfully and the SSL stack should return immediately without calling the resume callback yet.
Return:: MBEDTLS_ERR_SSL_HW_ACCEL_FALLTHROUGH if the external processor does not support this key. The SSL stack will use the private key object instead.
Return:: Any other error indicates a fatal failure and is propagated up the call chain. The callback should use MBEDTLS_ERR_PK_xxx error codes, and must not use MBEDTLS_ERR_SSL_xxx error codes except as directed in the documentation of this callback.

typedef int mbedtls_ssl_async_resume_t(mbedtls_ssl_context *ssl, unsigned char *output, size_t *output_len, size_t output_size)

Callback type: resume external operation.

             This callback is called during an SSL handshake to resume
             an external operation started by the
             ::mbedtls_ssl_async_sign_t or
             ::mbedtls_ssl_async_decrypt_t callback.

             This function typically checks the status of a pending
             request or causes the request queue to make progress, and
             does not wait for the operation to complete. This allows
             the handshake step to be non-blocking.

             This function may call mbedtls_ssl_get_async_operation_data()
             to retrieve an operation context set by the start callback.
             It may call mbedtls_ssl_set_async_operation_data() to modify
             this context.

             Note that when this function returns a status other than
             #MBEDTLS_ERR_SSL_ASYNC_IN_PROGRESS, it must free any
             resources associated with the operation.

Param ssl:: The SSL connection instance. It should not be modified other than via mbedtls_ssl_set_async_operation_data().
Param output:: Buffer containing the output (signature or decrypted data) on success.
Param output_len:: On success, number of bytes written to output.
Param output_size:: Size of the output buffer in bytes.
Return:: 0 if output of the operation is available in the output buffer.
Return:: MBEDTLS_ERR_SSL_ASYNC_IN_PROGRESS if the operation is still in progress. Subsequent requests for progress on the SSL connection will call the resume callback again.
Return:: Any other error means that the operation is aborted. The SSL handshake is aborted. The callback should use MBEDTLS_ERR_PK_xxx error codes, and must not use MBEDTLS_ERR_SSL_xxx error codes except as directed in the documentation of this callback.

typedef void mbedtls_ssl_async_cancel_t(mbedtls_ssl_context *ssl)

Callback type: cancel external operation.

             This callback is called if an SSL connection is closed
             while an asynchronous operation is in progress. Note that
             this callback is not called if the
             ::mbedtls_ssl_async_resume_t callback has run and has
             returned a value other than
             #MBEDTLS_ERR_SSL_ASYNC_IN_PROGRESS, since in that case
             the asynchronous operation has already completed.

             This function may call mbedtls_ssl_get_async_operation_data()
             to retrieve an operation context set by the start callback.

Param ssl:: The SSL connection instance. It should not be modified.

typedef uint16_t mbedtls_ssl_srtp_profile

typedef struct mbedtls_dtls_srtp_info_t mbedtls_dtls_srtp_info

typedef int mbedtls_ssl_ticket_write_t(void *p_ticket, const mbedtls_ssl_session *session, unsigned char *start, const unsigned char *end, size_t *tlen, uint32_t *lifetime)

Callback type: generate and write session ticket.

Note

This describes what a callback implementation should do. This callback should generate an encrypted and authenticated ticket for the session and write it to the output buffer. Here, ticket means the opaque ticket part of the NewSessionTicket structure of RFC 5077.

Param p_ticket:: Context for the callback
Param session:: SSL session to be written in the ticket
Param start:: Start of the output buffer
Param end:: End of the output buffer
Param tlen:: On exit, holds the length written
Param lifetime:: On exit, holds the lifetime of the ticket in seconds
Return:: 0 if successful, or a specific MBEDTLS_ERR_XXX code.

typedef int mbedtls_ssl_export_keys_t(void *p_expkey, const unsigned char *ms, const unsigned char *kb, size_t maclen, size_t keylen, size_t ivlen)

Callback type: Export key block and master secret.

Note

This is required for certain uses of TLS, e.g. EAP-TLS (RFC 5216) and Thread. The key pointers are ephemeral and therefore must not be stored. The master secret and keys should not be used directly except as an input to a key derivation function.

Param p_expkey:: Context for the callback
Param ms:: Pointer to master secret (fixed length: 48 bytes)
Param kb:: Pointer to key block, see RFC 5246 section 6.3 (variable length: 2 * maclen + 2 * keylen + 2 * ivlen).
Param maclen:: MAC length
Param keylen:: Key length
Param ivlen:: IV length
Return:: 0 if successful, or a specific MBEDTLS_ERR_XXX code.

typedef int mbedtls_ssl_export_keys_ext_t(void *p_expkey, const unsigned char *ms, const unsigned char *kb, size_t maclen, size_t keylen, size_t ivlen, const unsigned char client_random[32], const unsigned char server_random[32], mbedtls_tls_prf_types tls_prf_type)

Callback type: Export key block, master secret, handshake randbytes and the tls_prf function used to derive keys.

Note

This is required for certain uses of TLS, e.g. EAP-TLS (RFC 5216) and Thread. The key pointers are ephemeral and therefore must not be stored. The master secret and keys should not be used directly except as an input to a key derivation function.

Param p_expkey:: Context for the callback.
Param ms:: Pointer to master secret (fixed length: 48 bytes).
Param kb:: Pointer to key block, see RFC 5246 section 6.3. (variable length: 2 * maclen + 2 * keylen + 2 * ivlen).
Param maclen:: MAC length.
Param keylen:: Key length.
Param ivlen:: IV length.
Param client_random:: The client random bytes.
Param server_random:: The server random bytes.
Param tls_prf_type:: The tls_prf enum type.
Return:: 0 if successful, or a specific MBEDTLS_ERR_XXX code.

typedef int mbedtls_ssl_ticket_parse_t(void *p_ticket, mbedtls_ssl_session *session, unsigned char *buf, size_t len)

Callback type: parse and load session ticket.

Note

This describes what a callback implementation should do. This callback should parse a session ticket as generated by the corresponding mbedtls_ssl_ticket_write_t function, and, if the ticket is authentic and valid, load the session.

Note

The implementation is allowed to modify the first len bytes of the input buffer, eg to use it as a temporary area for the decrypted ticket contents.

Param p_ticket:: Context for the callback
Param session:: SSL session to be loaded
Param buf:: Start of the buffer containing the ticket
Param len:: Length of the ticket.
Return:: 0 if successful, or MBEDTLS_ERR_SSL_INVALID_MAC if not authentic, or MBEDTLS_ERR_SSL_SESSION_TICKET_EXPIRED if expired, or any other non-zero code for other failures.

typedef int mbedtls_ssl_cookie_write_t(void *ctx, unsigned char **p, unsigned char *end, const unsigned char *info, size_t ilen)

Callback type: generate a cookie.

Param ctx:: Context for the callback
Param p:: Buffer to write to, must be updated to point right after the cookie
Param end:: Pointer to one past the end of the output buffer
Param info:: Client ID info that was passed to mbedtls_ssl_set_client_transport_id()
Param ilen:: Length of info in bytes
Return:: The callback must return 0 on success, or a negative error code.

typedef int mbedtls_ssl_cookie_check_t(void *ctx, const unsigned char *cookie, size_t clen, const unsigned char *info, size_t ilen)

Callback type: verify a cookie.

Param ctx:: Context for the callback
Param cookie:: Cookie to verify
Param clen:: Length of cookie
Param info:: Client ID info that was passed to mbedtls_ssl_set_client_transport_id()
Param ilen:: Length of info in bytes
Return:: The callback must return 0 if cookie is valid, or a negative error code.

Enums

enum mbedtls_ssl_states

Values:

enumerator MBEDTLS_SSL_HELLO_REQUEST

enumerator MBEDTLS_SSL_CLIENT_HELLO

enumerator MBEDTLS_SSL_SERVER_HELLO

enumerator MBEDTLS_SSL_SERVER_CERTIFICATE

enumerator MBEDTLS_SSL_SERVER_KEY_EXCHANGE

enumerator MBEDTLS_SSL_CERTIFICATE_REQUEST

enumerator MBEDTLS_SSL_SERVER_HELLO_DONE

enumerator MBEDTLS_SSL_CLIENT_CERTIFICATE

enumerator MBEDTLS_SSL_CLIENT_KEY_EXCHANGE

enumerator MBEDTLS_SSL_CERTIFICATE_VERIFY

enumerator MBEDTLS_SSL_CLIENT_CHANGE_CIPHER_SPEC

enumerator MBEDTLS_SSL_CLIENT_FINISHED

enumerator MBEDTLS_SSL_SERVER_CHANGE_CIPHER_SPEC

enumerator MBEDTLS_SSL_SERVER_FINISHED

enumerator MBEDTLS_SSL_FLUSH_BUFFERS

enumerator MBEDTLS_SSL_HANDSHAKE_WRAPUP

enumerator MBEDTLS_SSL_HANDSHAKE_OVER

enumerator MBEDTLS_SSL_SERVER_NEW_SESSION_TICKET

enumerator MBEDTLS_SSL_SERVER_HELLO_VERIFY_REQUEST_SENT

enum mbedtls_tls_prf_types

Values:

enumerator MBEDTLS_SSL_TLS_PRF_NONE

enumerator MBEDTLS_SSL_TLS_PRF_SSL3

enumerator MBEDTLS_SSL_TLS_PRF_TLS1

enumerator MBEDTLS_SSL_TLS_PRF_SHA384

enumerator MBEDTLS_SSL_TLS_PRF_SHA256

Functions

const char *mbedtls_ssl_get_ciphersuite_name(const int ciphersuite_id)

Return the name of the ciphersuite associated with the given ID.

Parameters:: ciphersuite_id – SSL ciphersuite ID
Returns:: a string containing the ciphersuite name

int mbedtls_ssl_get_ciphersuite_id(const char *ciphersuite_name)

Return the ID of the ciphersuite associated with the given name.

Parameters:: ciphersuite_name – SSL ciphersuite name
Returns:: the ID with the ciphersuite or 0 if not found

void mbedtls_ssl_init(mbedtls_ssl_context *ssl)

Initialize an SSL context Just makes the context ready for mbedtls_ssl_setup() or mbedtls_ssl_free()

Parameters:: ssl – SSL context

int mbedtls_ssl_setup(mbedtls_ssl_context *ssl, const mbedtls_ssl_config *conf)

Set up an SSL context for use.

Note

No copy of the configuration context is made, it can be shared by many mbedtls_ssl_context structures.

Note

If MBEDTLS_USE_PSA_CRYPTO is enabled, the PSA crypto subsystem must have been initialized by calling psa_crypto_init() before calling this function.

Warning

The conf structure will be accessed during the session. It must not be modified or freed as long as the session is active.

Warning

This function must be called exactly once per context. Calling mbedtls_ssl_setup again is not supported, even if no session is active.

Warning

After setting up a client context, if certificate-based authentication is enabled, you should call mbedtls_ssl_set_hostname() to specifiy the expected name of the server. Without this, in most scenarios, the TLS connection is insecure. See MBEDTLS_ERR_SSL_CERTIFICATE_VERIFICATION_WITHOUT_HOSTNAME for more information.

Parameters:

ssl – SSL context
conf – SSL configuration to use

Returns:

0 if successful, or MBEDTLS_ERR_SSL_ALLOC_FAILED if memory allocation failed

int mbedtls_ssl_session_reset(mbedtls_ssl_context *ssl)

Reset an already initialized SSL context for re-use while retaining application-set variables, function pointers and data.

Parameters:: ssl – SSL context
Returns:: 0 if successful, or MBEDTLS_ERR_SSL_ALLOC_FAILED, MBEDTLS_ERR_SSL_HW_ACCEL_FAILED or MBEDTLS_ERR_SSL_COMPRESSION_FAILED

void mbedtls_ssl_conf_endpoint(mbedtls_ssl_config *conf, int endpoint)

Set the current endpoint type.

Parameters:

conf – SSL configuration
endpoint – must be MBEDTLS_SSL_IS_CLIENT or MBEDTLS_SSL_IS_SERVER

void mbedtls_ssl_conf_transport(mbedtls_ssl_config *conf, int transport)

Set the transport type (TLS or DTLS). Default: TLS.

Note

For DTLS, you must either provide a recv callback that doesn’t block, or one that handles timeouts, see mbedtls_ssl_set_bio(). You also need to provide timer callbacks with mbedtls_ssl_set_timer_cb().

Parameters:

conf – SSL configuration
transport – transport type: MBEDTLS_SSL_TRANSPORT_STREAM for TLS, MBEDTLS_SSL_TRANSPORT_DATAGRAM for DTLS.

void mbedtls_ssl_conf_authmode(mbedtls_ssl_config *conf, int authmode)

Set the certificate verification mode Default: NONE on server, REQUIRED on client.

MBEDTLS_SSL_VERIFY_NONE: peer certificate is not checked (default on server) (insecure on client)

MBEDTLS_SSL_VERIFY_OPTIONAL: peer certificate is checked, however the handshake continues even if verification failed; mbedtls_ssl_get_verify_result() can be called after the handshake is complete.

MBEDTLS_SSL_VERIFY_REQUIRED: peer must present a valid certificate, handshake is aborted if verification failed. (default on client)

Note

On client, MBEDTLS_SSL_VERIFY_REQUIRED is the recommended mode. With MBEDTLS_SSL_VERIFY_OPTIONAL, the user needs to call mbedtls_ssl_get_verify_result() at the right time(s), which may not be obvious, while REQUIRED always perform the verification as soon as possible. For example, REQUIRED was protecting against the “triple handshake” attack even before it was found.

Parameters:

conf – SSL configuration
authmode – can be:

void mbedtls_ssl_conf_verify(mbedtls_ssl_config *conf, int (*f_vrfy)(void*, mbedtls_x509_crt*, int, uint32_t*), void *p_vrfy)

Set the verification callback (Optional).

            If set, the provided verify callback is called for each
            certificate in the peer's CRT chain, including the trusted
            root. For more information, please see the documentation of
            \c mbedtls_x509_crt_verify().

Note

For per context callbacks and contexts, please use mbedtls_ssl_set_verify() instead.

Parameters:

conf – The SSL configuration to use.
f_vrfy – The verification callback to use during CRT verification.
p_vrfy – The opaque context to be passed to the callback.

void mbedtls_ssl_conf_rng(mbedtls_ssl_config *conf, int (*f_rng)(void*, unsigned char*, size_t), void *p_rng)

Set the random number generator callback.

Parameters:

conf – SSL configuration
f_rng – RNG function
p_rng – RNG parameter

void mbedtls_ssl_conf_dbg(mbedtls_ssl_config *conf, void (*f_dbg)(void*, int, const char*, int, const char*), void *p_dbg)

Set the debug callback.

            The callback has the following argument:
            void *           opaque context for the callback
            int              debug level
            const char *     file name
            int              line number
            const char *     message

Parameters:

conf – SSL configuration
f_dbg – debug function
p_dbg – debug parameter

void mbedtls_ssl_set_bio(mbedtls_ssl_context *ssl, void *p_bio, mbedtls_ssl_send_t *f_send, mbedtls_ssl_recv_t *f_recv, mbedtls_ssl_recv_timeout_t *f_recv_timeout)

Set the underlying BIO callbacks for write, read and read-with-timeout.

Note

One of f_recv or f_recv_timeout can be NULL, in which case the other is used. If both are non-NULL, f_recv_timeout is used and f_recv is ignored (as if it were NULL).

Note

The two most common use cases are:

non-blocking I/O, f_recv != NULL, f_recv_timeout == NULL
blocking I/O, f_recv == NULL, f_recv_timeout != NULL

Note

For DTLS, you need to provide either a non-NULL f_recv_timeout callback, or a f_recv that doesn’t block.

Note

See the documentations of mbedtls_ssl_send_t, mbedtls_ssl_recv_t and mbedtls_ssl_recv_timeout_t for the conventions those callbacks must follow.

Note

On some platforms, net_sockets.c provides mbedtls_net_send(), mbedtls_net_recv() and mbedtls_net_recv_timeout() that are suitable to be used here.

Parameters:

ssl – SSL context
p_bio – parameter (context) shared by BIO callbacks
f_send – write callback
f_recv – read callback
f_recv_timeout – blocking read callback with timeout.

int mbedtls_ssl_set_cid(mbedtls_ssl_context *ssl, int enable, unsigned char const *own_cid, size_t own_cid_len)

Configure the use of the Connection ID (CID) extension in the next handshake.

Reference: draft-ietf-tls-dtls-connection-id-05 https://tools.ietf.org/html/draft-ietf-tls-dtls-connection-id-05

The DTLS CID extension allows the reliable association of DTLS records to DTLS connections across changes in the underlying transport (changed IP and Port metadata) by adding explicit connection identifiers (CIDs) to the headers of encrypted DTLS records. The desired CIDs are configured by the application layer and are exchanged in new ClientHello / ServerHello extensions during the handshake, where each side indicates the CID it wants the peer to use when writing encrypted messages. The CIDs are put to use once records get encrypted: the stack discards any incoming records that don’t include the configured CID in their header, and adds the peer’s requested CID to the headers of outgoing messages.

This API enables or disables the use of the CID extension in the next handshake and sets the value of the CID to be used for incoming messages.

Note

The value of own_cid_len must match the value of the len parameter passed to mbedtls_ssl_conf_cid() when configuring the mbedtls_ssl_config that ssl is bound to.

Note

This CID configuration applies to subsequent handshakes performed on the SSL context ssl, but does not trigger one. You still have to call mbedtls_ssl_handshake() (for the initial handshake) or mbedtls_ssl_renegotiate() (for a renegotiation handshake) explicitly after a successful call to this function to run the handshake.

Note

This call cannot guarantee that the use of the CID will be successfully negotiated in the next handshake, because the peer might not support it. Specifically:

On the Client, enabling the use of the CID through this call implies that the ClientHello in the next handshake will include the CID extension, thereby offering the use of the CID to the server. Only if the ServerHello contains the CID extension, too, the CID extension will actually be put to use.
On the Server, enabling the use of the CID through this call implies that that the server will look for the CID extension in a ClientHello from the client, and, if present, reply with a CID extension in its ServerHello.

Note

To check whether the use of the CID was negotiated after the subsequent handshake has completed, please use the API mbedtls_ssl_get_peer_cid().

Warning

If the use of the CID extension is enabled in this call and the subsequent handshake negotiates its use, Mbed TLS will silently drop every packet whose CID does not match the CID configured in own_cid. It is the responsibility of the user to adapt the underlying transport to take care of CID-based demultiplexing before handing datagrams to Mbed TLS.

Parameters:

ssl – The SSL context to configure. This must be initialized.
enable – This value determines whether the CID extension should be used or not. Possible values are:
- MBEDTLS_SSL_CID_ENABLED to enable the use of the CID.
- MBEDTLS_SSL_CID_DISABLED (default) to disable the use of the CID.
own_cid – The address of the readable buffer holding the CID we want the peer to use when sending encrypted messages to us. This may be NULL if own_cid_len is 0. This parameter is unused if enable is set to MBEDTLS_SSL_CID_DISABLED.
own_cid_len – The length of own_cid. This parameter is unused if enable is set to MBEDTLS_SSL_CID_DISABLED.

Returns:

0 on success. In this case, the CID configuration applies to the next handshake.

Returns:

A negative error code on failure.

int mbedtls_ssl_get_peer_cid(mbedtls_ssl_context *ssl, int *enabled, unsigned char peer_cid[MBEDTLS_SSL_CID_OUT_LEN_MAX], size_t *peer_cid_len)

Get information about the use of the CID extension in the current connection.

Note

This applies to the state of the CID negotiated in the last complete handshake. If a handshake is in progress, this function will attempt to complete the handshake first.

Note

If CID extensions have been exchanged but both client and server chose to use an empty CID, this function sets *enabled to MBEDTLS_SSL_CID_DISABLED (the rationale for this is that the resulting communication is the same as if the CID extensions hadn’t been used).

Parameters:

ssl – The SSL context to query.
enabled – The address at which to store whether the CID extension is currently in use or not. If the CID is in use, *enabled is set to MBEDTLS_SSL_CID_ENABLED; otherwise, it is set to MBEDTLS_SSL_CID_DISABLED.
peer_cid – The address of the buffer in which to store the CID chosen by the peer (if the CID extension is used). This may be NULL in case the value of peer CID isn’t needed. If it is not NULL, peer_cid_len must not be NULL.
peer_cid_len – The address at which to store the size of the CID chosen by the peer (if the CID extension is used). This is also the number of Bytes in peer_cid that have been written. This may be NULL in case the length of the peer CID isn’t needed. If it is NULL, peer_cid must be NULL, too.

Returns:

0 on success.

Returns:

A negative error code on failure.

void mbedtls_ssl_set_mtu(mbedtls_ssl_context *ssl, uint16_t mtu)

Set the Maximum Transport Unit (MTU). Special value: 0 means unset (no limit). This represents the maximum size of a datagram payload handled by the transport layer (usually UDP) as determined by the network link and stack. In practice, this controls the maximum size datagram the DTLS layer will pass to the f_send() callback set using mbedtls_ssl_set_bio().

Note

The limit on datagram size is converted to a limit on record payload by subtracting the current overhead of encapsulation and encryption/authentication if any.

Note

This can be called at any point during the connection, for example when a Path Maximum Transfer Unit (PMTU) estimate becomes available from other sources, such as lower (or higher) protocol layers.

Note

This setting only controls the size of the packets we send, and does not restrict the size of the datagrams we’re willing to receive. Client-side, you can request the server to use smaller records with mbedtls_ssl_conf_max_frag_len().

Note

If both a MTU and a maximum fragment length have been configured (or negotiated with the peer), the resulting lower limit on record payload (see first note) is used.

Note

This can only be used to decrease the maximum size of datagrams (hence records, see first note) sent. It cannot be used to increase the maximum size of records over the limit set by MBEDTLS_SSL_OUT_CONTENT_LEN.

Note

Values lower than the current record layer expansion will result in an error when trying to send data.

Note

Using record compression together with a non-zero MTU value will result in an error when trying to send data.

Parameters:

ssl – SSL context
mtu – Value of the path MTU in bytes

void mbedtls_ssl_set_verify(mbedtls_ssl_context *ssl, int (*f_vrfy)(void*, mbedtls_x509_crt*, int, uint32_t*), void *p_vrfy)

Set a connection-specific verification callback (optional).

            If set, the provided verify callback is called for each
            certificate in the peer's CRT chain, including the trusted
            root. For more information, please see the documentation of
            \c mbedtls_x509_crt_verify().

Note

This call is analogous to mbedtls_ssl_conf_verify() but binds the verification callback and context to an SSL context as opposed to an SSL configuration. If mbedtls_ssl_conf_verify() and mbedtls_ssl_set_verify() are both used, mbedtls_ssl_set_verify() takes precedence.

Parameters:

ssl – The SSL context to use.
f_vrfy – The verification callback to use during CRT verification.
p_vrfy – The opaque context to be passed to the callback.

void mbedtls_ssl_conf_read_timeout(mbedtls_ssl_config *conf, uint32_t timeout)

Set the timeout period for mbedtls_ssl_read() (Default: no timeout.)

Note

With blocking I/O, this will only work if a non-NULL f_recv_timeout was set with mbedtls_ssl_set_bio(). With non-blocking I/O, this will only work if timer callbacks were set with mbedtls_ssl_set_timer_cb().

Note

With non-blocking I/O, you may also skip this function altogether and handle timeouts at the application layer.

Parameters:

conf – SSL configuration context
timeout – Timeout value in milliseconds. Use 0 for no timeout (default).

int mbedtls_ssl_check_record(mbedtls_ssl_context const *ssl, unsigned char *buf, size_t buflen)

Check whether a buffer contains a valid and authentic record that has not been seen before. (DTLS only).

This function does not change the user-visible state of the SSL context. Its sole purpose is to provide an indication of the legitimacy of an incoming record.

This can be useful e.g. in distributed server environments using the DTLS Connection ID feature, in which connections might need to be passed between service instances on a change of peer address, but where such disruptive operations should only happen after the validity of incoming records has been confirmed.

Note

This routine only checks whether the provided buffer begins with a valid and authentic record that has not been seen before, but does not check potential data following the initial record. In particular, it is possible to pass DTLS datagrams containing multiple records, in which case only the first record is checked.

Note

This function modifies the input buffer buf. If you need to preserve the original record, you have to maintain a copy.

Parameters:

ssl – The SSL context to use.
buf – The address of the buffer holding the record to be checked. This must be a read/write buffer of length buflen Bytes.
buflen – The length of buf in Bytes.

Returns:

0 if the record is valid and authentic and has not been seen before.

Returns:

MBEDTLS_ERR_SSL_INVALID_MAC if the check completed successfully but the record was found to be not authentic.

Returns:

MBEDTLS_ERR_SSL_INVALID_RECORD if the check completed successfully but the record was found to be invalid for a reason different from authenticity checking.

Returns:

MBEDTLS_ERR_SSL_UNEXPECTED_RECORD if the check completed successfully but the record was found to be unexpected in the state of the SSL context, including replayed records.

Returns:

Another negative error code on different kinds of failure. In this case, the SSL context becomes unusable and needs to be freed or reset before reuse.

void mbedtls_ssl_set_timer_cb(mbedtls_ssl_context *ssl, void *p_timer, mbedtls_ssl_set_timer_t *f_set_timer, mbedtls_ssl_get_timer_t *f_get_timer)

Set the timer callbacks (Mandatory for DTLS.)

Note

See the documentation of mbedtls_ssl_set_timer_t and mbedtls_ssl_get_timer_t for the conventions this pair of callbacks must follow.

Note

On some platforms, timing.c provides mbedtls_timing_set_delay() and mbedtls_timing_get_delay() that are suitable for using here, except if using an event-driven style.

Note

See also the “DTLS tutorial” article in our knowledge base. https://mbed-tls.readthedocs.io/en/latest/kb/how-to/dtls-tutorial

Parameters:

ssl – SSL context
p_timer – parameter (context) shared by timer callbacks
f_set_timer – set timer callback
f_get_timer – get timer callback. Must return:

void mbedtls_ssl_conf_session_tickets_cb(mbedtls_ssl_config *conf, mbedtls_ssl_ticket_write_t *f_ticket_write, mbedtls_ssl_ticket_parse_t *f_ticket_parse, void *p_ticket)

Configure SSL session ticket callbacks (server only). (Default: none.)

Note

On server, session tickets are enabled by providing non-NULL callbacks.

Note

On client, use mbedtls_ssl_conf_session_tickets().

Parameters:

conf – SSL configuration context
f_ticket_write – Callback for writing a ticket
f_ticket_parse – Callback for parsing a ticket
p_ticket – Context shared by the two callbacks

void mbedtls_ssl_conf_export_keys_cb(mbedtls_ssl_config *conf, mbedtls_ssl_export_keys_t *f_export_keys, void *p_export_keys)

Configure key export callback. (Default: none.)

Note

See mbedtls_ssl_export_keys_t.

Parameters:

conf – SSL configuration context
f_export_keys – Callback for exporting keys
p_export_keys – Context for the callback

void mbedtls_ssl_conf_export_keys_ext_cb(mbedtls_ssl_config *conf, mbedtls_ssl_export_keys_ext_t *f_export_keys_ext, void *p_export_keys)

Configure extended key export callback. (Default: none.)

Note

See mbedtls_ssl_export_keys_ext_t.

Warning

Exported key material must not be used for any purpose before the (D)TLS handshake is completed

Parameters:

conf – SSL configuration context
f_export_keys_ext – Callback for exporting keys
p_export_keys – Context for the callback

void mbedtls_ssl_conf_async_private_cb(mbedtls_ssl_config *conf, mbedtls_ssl_async_sign_t *f_async_sign, mbedtls_ssl_async_decrypt_t *f_async_decrypt, mbedtls_ssl_async_resume_t *f_async_resume, mbedtls_ssl_async_cancel_t *f_async_cancel, void *config_data)

Configure asynchronous private key operation callbacks.

Parameters:

conf – SSL configuration context
f_async_sign – Callback to start a signature operation. See the description of mbedtls_ssl_async_sign_t for more information. This may be NULL if the external processor does not support any signature operation; in this case the private key object associated with the certificate will be used.
f_async_decrypt – Callback to start a decryption operation. See the description of mbedtls_ssl_async_decrypt_t for more information. This may be NULL if the external processor does not support any decryption operation; in this case the private key object associated with the certificate will be used.
f_async_resume – Callback to resume an asynchronous operation. See the description of mbedtls_ssl_async_resume_t for more information. This may not be NULL unless f_async_sign and f_async_decrypt are both NULL.
f_async_cancel – Callback to cancel an asynchronous operation. See the description of mbedtls_ssl_async_cancel_t for more information. This may be NULL if no cleanup is needed.
config_data – A pointer to configuration data which can be retrieved with mbedtls_ssl_conf_get_async_config_data(). The library stores this value without dereferencing it.

void *mbedtls_ssl_conf_get_async_config_data(const mbedtls_ssl_config *conf)

Retrieve the configuration data set by mbedtls_ssl_conf_async_private_cb().

Parameters:: conf – SSL configuration context
Returns:: The configuration data set by mbedtls_ssl_conf_async_private_cb().

void *mbedtls_ssl_get_async_operation_data(const mbedtls_ssl_context *ssl)

Retrieve the asynchronous operation user context.

Note

This function may only be called while a handshake is in progress.

Parameters:: ssl – The SSL context to access.
Returns:: The asynchronous operation user context that was last set during the current handshake. If mbedtls_ssl_set_async_operation_data() has not yet been called during the current handshake, this function returns NULL.

void mbedtls_ssl_set_async_operation_data(mbedtls_ssl_context *ssl, void *ctx)

Retrieve the asynchronous operation user context.

Note

This function may only be called while a handshake is in progress.

Parameters:

ssl – The SSL context to access.
ctx – The new value of the asynchronous operation user context. Call mbedtls_ssl_get_async_operation_data() later during the same handshake to retrieve this value.

void mbedtls_ssl_conf_dtls_cookies(mbedtls_ssl_config *conf, mbedtls_ssl_cookie_write_t *f_cookie_write, mbedtls_ssl_cookie_check_t *f_cookie_check, void *p_cookie)

Register callbacks for DTLS cookies (Server only. DTLS only.)

Default: dummy callbacks that fail, in order to force you to register working callbacks (and initialize their context).

To disable HelloVerifyRequest, register NULL callbacks.

Note

See comments on mbedtls_ssl_handshake() about handling the MBEDTLS_ERR_SSL_HELLO_VERIFY_REQUIRED that is expected on the first handshake attempt when this is enabled.

Note

This is also necessary to handle client reconnection from the same port as described in RFC 6347 section 4.2.8 (only the variant with cookies is supported currently). See comments on mbedtls_ssl_read() for details.

Warning

Disabling hello verification allows your server to be used for amplification in DoS attacks against other hosts. Only disable if you known this can’t happen in your particular environment.

Parameters:

conf – SSL configuration
f_cookie_write – Cookie write callback
f_cookie_check – Cookie check callback
p_cookie – Context for both callbacks

int mbedtls_ssl_set_client_transport_id(mbedtls_ssl_context *ssl, const unsigned char *info, size_t ilen)

Set client’s transport-level identification info. (Server only. DTLS only.)

This is usually the IP address (and port), but could be anything identify the client depending on the underlying network stack. Used for HelloVerifyRequest with DTLS. This is not used to route the actual packets.

Note

An internal copy is made, so the info buffer can be reused.

Parameters:

ssl – SSL context
info – Transport-level info identifying the client (eg IP + port)
ilen – Length of info in bytes

Returns:

0 on success, MBEDTLS_ERR_SSL_BAD_INPUT_DATA if used on client, MBEDTLS_ERR_SSL_ALLOC_FAILED if out of memory.

void mbedtls_ssl_conf_dtls_anti_replay(mbedtls_ssl_config *conf, char mode)

Enable or disable anti-replay protection for DTLS. (DTLS only, no effect on TLS.) Default: enabled.

Warning

Disabling this is a security risk unless the application protocol handles duplicated packets in a safe way. You should not disable this without careful consideration. However, if your application already detects duplicated packets and needs information about them to adjust its transmission strategy, then you’ll want to disable this.

Parameters:

conf – SSL configuration
mode – MBEDTLS_SSL_ANTI_REPLAY_ENABLED or MBEDTLS_SSL_ANTI_REPLAY_DISABLED.

void mbedtls_ssl_conf_dtls_badmac_limit(mbedtls_ssl_config *conf, unsigned limit)

Set a limit on the number of records with a bad MAC before terminating the connection. (DTLS only, no effect on TLS.) Default: 0 (disabled).

Note

If the limit is N, then the connection is terminated when the Nth non-authentic record is seen.

Note

Records with an invalid header are not counted, only the ones going through the authentication-decryption phase.

Note

This is a security trade-off related to the fact that it’s often relatively easy for an active attacker to inject UDP datagrams. On one hand, setting a low limit here makes it easier for such an attacker to forcibly terminated a connection. On the other hand, a high limit or no limit might make us waste resources checking authentication on many bogus packets.

Parameters:

conf – SSL configuration
limit – Limit, or 0 to disable.

void mbedtls_ssl_set_datagram_packing(mbedtls_ssl_context *ssl, unsigned allow_packing)

Allow or disallow packing of multiple handshake records within a single datagram.

Note

This is enabled by default and should only be disabled for test purposes, or if datagram packing causes interoperability issues with peers that don’t support it.

Note

Allowing datagram packing reduces the network load since there’s less overhead if multiple messages share the same datagram. Also, it increases the handshake efficiency since messages belonging to a single datagram will not be reordered in transit, and so future message buffering or flight retransmission (if no buffering is used) as means to deal with reordering are needed less frequently.

Note

Application records are not affected by this option and are currently always sent in separate datagrams.

Parameters:

ssl – The SSL context to configure.
allow_packing – This determines whether datagram packing may be used or not. A value of 0 means that every record will be sent in a separate datagram; a value of 1 means that, if space permits, multiple handshake messages (including CCS) belonging to a single flight may be packed within a single datagram.

void mbedtls_ssl_conf_handshake_timeout(mbedtls_ssl_config *conf, uint32_t min, uint32_t max)

Set retransmit timeout values for the DTLS handshake. (DTLS only, no effect on TLS.)

Note

Default values are from RFC 6347 section 4.2.4.1.

Note

The ‘min’ value should typically be slightly above the expected round-trip time to your peer, plus whatever time it takes for the peer to process the message. For example, if your RTT is about 600ms and you peer needs up to 1s to do the cryptographic operations in the handshake, then you should set ‘min’ slightly above 1600. Lower values of ‘min’ might cause spurious resends which waste network resources, while larger value of ‘min’ will increase overall latency on unreliable network links.

Note

The more unreliable your network connection is, the larger your max / min ratio needs to be in order to achieve reliable handshakes.

Note

Messages are retransmitted up to log2(ceil(max/min)) times. For example, if min = 1s and max = 5s, the retransmit plan goes: send … 1s -> resend … 2s -> resend … 4s -> resend … 5s -> give up and return a timeout error.

Parameters:

conf – SSL configuration
min – Initial timeout value in milliseconds. Default: 1000 (1 second).
max – Maximum timeout value in milliseconds. Default: 60000 (60 seconds).

void mbedtls_ssl_conf_session_cache(mbedtls_ssl_config *conf, void *p_cache, int (*f_get_cache)(void*, mbedtls_ssl_session*), int (*f_set_cache)(void*, const mbedtls_ssl_session*))

Set the session cache callbacks (server-side only) If not set, no session resuming is done (except if session tickets are enabled too).

The session cache has the responsibility to check for stale entries based on timeout. See RFC 5246 for recommendations.

Warning: session.peer_cert is cleared by the SSL/TLS layer on connection shutdown, so do not cache the pointer! Either set it to NULL or make a full copy of the certificate.

The get callback is called once during the initial handshake to enable session resuming. The get function has the following parameters: (void *parameter, mbedtls_ssl_session *session) If a valid entry is found, it should fill the master of the session object with the cached values and return 0, return 1 otherwise. Optionally peer_cert can be set as well if it is properly present in cache entry.

The set callback is called once during the initial handshake to enable session resuming after the entire handshake has been finished. The set function has the following parameters: (void *parameter, const mbedtls_ssl_session *session). The function should create a cache entry for future retrieval based on the data in the session structure and should keep in mind that the mbedtls_ssl_session object presented (and all its referenced data) is cleared by the SSL/TLS layer when the connection is terminated. It is recommended to add metadata to determine if an entry is still valid in the future. Return 0 if successfully cached, return 1 otherwise.

Parameters:

conf – SSL configuration
p_cache – parameter (context) for both callbacks
f_get_cache – session get callback
f_set_cache – session set callback

int mbedtls_ssl_set_session(mbedtls_ssl_context *ssl, const mbedtls_ssl_session *session)

Request resumption of session (client-side only) Session data is copied from presented session structure.

See also

mbedtls_ssl_get_session()

Parameters:

ssl – SSL context
session – session context

Returns:

0 if successful, MBEDTLS_ERR_SSL_ALLOC_FAILED if memory allocation failed, MBEDTLS_ERR_SSL_BAD_INPUT_DATA if used server-side or arguments are otherwise invalid

int mbedtls_ssl_session_load(mbedtls_ssl_session *session, const unsigned char *buf, size_t len)

Load serialized session data into a session structure. On client, this can be used for loading saved sessions before resuming them with mbedtls_ssl_set_session(). On server, this can be used for alternative implementations of session cache or session tickets.

See also

mbedtls_ssl_session_save()

See also

mbedtls_ssl_set_session()

Warning

If a peer certificate chain is associated with the session, the serialized state will only contain the peer’s end-entity certificate and the result of the chain verification (unless verification was disabled), but not the rest of the chain.

Parameters:

session – The session structure to be populated. It must have been initialised with mbedtls_ssl_session_init() but not populated yet.
buf – The buffer holding the serialized session data. It must be a readable buffer of at least len bytes.
len – The size of the serialized data in bytes.

Returns:

0 if successful.

Returns:

MBEDTLS_ERR_SSL_ALLOC_FAILED if memory allocation failed.

Returns:

MBEDTLS_ERR_SSL_BAD_INPUT_DATA if input data is invalid.

Returns:

MBEDTLS_ERR_SSL_VERSION_MISMATCH if the serialized data was generated in a different version or configuration of Mbed TLS.

Returns:

Another negative value for other kinds of errors (for example, unsupported features in the embedded certificate).

int mbedtls_ssl_session_save(const mbedtls_ssl_session *session, unsigned char *buf, size_t buf_len, size_t *olen)

Save session structure as serialized data in a buffer. On client, this can be used for saving session data, potentially in non-volatile storage, for resuming later. On server, this can be used for alternative implementations of session cache or session tickets.

See also

mbedtls_ssl_session_load()

See also

mbedtls_ssl_get_session_pointer()

Note

olen is updated to the correct value regardless of whether buf_len was large enough. This makes it possible to determine the necessary size by calling this function with buf set to NULL and buf_len to 0.

Parameters:

session – The session structure to be saved.
buf – The buffer to write the serialized data to. It must be a writeable buffer of at least buf_len bytes, or may be NULL if buf_len is 0.
buf_len – The number of bytes available for writing in buf.
olen – The size in bytes of the data that has been or would have been written. It must point to a valid size_t.

Returns:

0 if successful.

Returns:

MBEDTLS_ERR_SSL_BUFFER_TOO_SMALL if buf is too small.

const mbedtls_ssl_session *mbedtls_ssl_get_session_pointer(const mbedtls_ssl_context *ssl)

Get a pointer to the current session structure, for example to serialize it.

See also

mbedtls_ssl_session_save()

Warning

Ownership of the session remains with the SSL context, and the returned pointer is only guaranteed to be valid until the next API call operating on the same ssl context.

Parameters:: ssl – The SSL context.
Returns:: A pointer to the current session if successful.
Returns:: NULL if no session is active.

void mbedtls_ssl_conf_ciphersuites(mbedtls_ssl_config *conf, const int *ciphersuites)

Set the list of allowed ciphersuites and the preference order. First in the list has the highest preference. (Overrides all version-specific lists)

The ciphersuites array is not copied, and must remain valid for the lifetime of the ssl_config.

Note: The server uses its own preferences over the preference of the client unless MBEDTLS_SSL_SRV_RESPECT_CLIENT_PREFERENCE is defined!

Parameters:

conf – SSL configuration
ciphersuites – 0-terminated list of allowed ciphersuites

int mbedtls_ssl_conf_cid(mbedtls_ssl_config *conf, size_t len, int ignore_other_cids)

Specify the length of Connection IDs for incoming encrypted DTLS records, as well as the behaviour on unexpected CIDs.

By default, the CID length is set to 0, and unexpected CIDs are silently ignored.

Note

The CID specification allows implementations to either use a common length for all incoming connection IDs or allow variable-length incoming IDs. Mbed TLS currently requires a common length for all connections sharing the same SSL configuration; this allows simpler parsing of record headers.

Parameters:

conf – The SSL configuration to modify.
len – The length in Bytes of the CID fields in encrypted DTLS records using the CID mechanism. This must not be larger than MBEDTLS_SSL_CID_OUT_LEN_MAX.
ignore_other_cids – This determines the stack’s behaviour when receiving a record with an unexpected CID. Possible values are:
- MBEDTLS_SSL_UNEXPECTED_CID_IGNORE In this case, the record is silently ignored.
- MBEDTLS_SSL_UNEXPECTED_CID_FAIL In this case, the stack fails with the specific error code MBEDTLS_ERR_SSL_UNEXPECTED_CID.

Returns:

0 on success.

Returns:

MBEDTLS_ERR_SSL_BAD_INPUT_DATA if len is too large.

void mbedtls_ssl_conf_ciphersuites_for_version(mbedtls_ssl_config *conf, const int *ciphersuites, int major, int minor)

Set the list of allowed ciphersuites and the preference order for a specific version of the protocol. (Only useful on the server side)

The ciphersuites array is not copied, and must remain valid for the lifetime of the ssl_config.

Note

With DTLS, use MBEDTLS_SSL_MINOR_VERSION_2 for DTLS 1.0 and MBEDTLS_SSL_MINOR_VERSION_3 for DTLS 1.2

Parameters:

conf – SSL configuration
ciphersuites – 0-terminated list of allowed ciphersuites
major – Major version number (only MBEDTLS_SSL_MAJOR_VERSION_3 supported)
minor – Minor version number (MBEDTLS_SSL_MINOR_VERSION_0, MBEDTLS_SSL_MINOR_VERSION_1 and MBEDTLS_SSL_MINOR_VERSION_2, MBEDTLS_SSL_MINOR_VERSION_3 supported)

void mbedtls_ssl_conf_cert_profile(mbedtls_ssl_config *conf, const mbedtls_x509_crt_profile *profile)

Set the X.509 security profile used for verification.

Note

The restrictions are enforced for all certificates in the chain. However, signatures in the handshake are not covered by this setting but by mbedtls_ssl_conf_sig_hashes().

Parameters:

conf – SSL configuration
profile – Profile to use

void mbedtls_ssl_conf_ca_chain(mbedtls_ssl_config *conf, mbedtls_x509_crt *ca_chain, mbedtls_x509_crl *ca_crl)

Set the data required to verify peer certificate.

Note

See mbedtls_x509_crt_verify() for notes regarding the parameters ca_chain (maps to trust_ca for that function) and ca_crl.

Parameters:

conf – SSL configuration
ca_chain – trusted CA chain (meaning all fully trusted top-level CAs)
ca_crl – trusted CA CRLs

void mbedtls_ssl_conf_ca_cb(mbedtls_ssl_config *conf, mbedtls_x509_crt_ca_cb_t f_ca_cb, void *p_ca_cb)

Set the trusted certificate callback.

            This API allows to register the set of trusted certificates
            through a callback, instead of a linked list as configured
            by mbedtls_ssl_conf_ca_chain().

            This is useful for example in contexts where a large number
            of CAs are used, and the inefficiency of maintaining them
            in a linked list cannot be tolerated. It is also useful when
            the set of trusted CAs needs to be modified frequently.

            See the documentation of `mbedtls_x509_crt_ca_cb_t` for
            more information.

Note

This API is incompatible with mbedtls_ssl_conf_ca_chain(): Any call to this function overwrites the values set through earlier calls to mbedtls_ssl_conf_ca_chain() or mbedtls_ssl_conf_ca_cb().

Note

This API is incompatible with CA indication in CertificateRequest messages: A server-side SSL context which is bound to an SSL configuration that uses a CA callback configured via mbedtls_ssl_conf_ca_cb(), and which requires client authentication, will send an empty CA list in the corresponding CertificateRequest message.

Note

This API is incompatible with mbedtls_ssl_set_hs_ca_chain(): If an SSL context is bound to an SSL configuration which uses CA callbacks configured via mbedtls_ssl_conf_ca_cb(), then calls to mbedtls_ssl_set_hs_ca_chain() have no effect.

Note

The use of this API disables the use of restartable ECC during X.509 CRT signature verification (but doesn’t affect other uses).

Warning

This API is incompatible with the use of CRLs. Any call to mbedtls_ssl_conf_ca_cb() unsets CRLs configured through earlier calls to mbedtls_ssl_conf_ca_chain().

Warning

In multi-threaded environments, the callback f_ca_cb must be thread-safe, and it is the user’s responsibility to guarantee this (for example through a mutex contained in the callback context pointed to by p_ca_cb).

Parameters:

conf – The SSL configuration to register the callback with.
f_ca_cb – The trusted certificate callback to use when verifying certificate chains.
p_ca_cb – The context to be passed to f_ca_cb (for example, a reference to a trusted CA database).

int mbedtls_ssl_conf_own_cert(mbedtls_ssl_config *conf, mbedtls_x509_crt *own_cert, mbedtls_pk_context *pk_key)

Set own certificate chain and private key.

Note

own_cert should contain in order from the bottom up your certificate chain. The top certificate (self-signed) can be omitted.

Note

On server, this function can be called multiple times to provision more than one cert/key pair (eg one ECDSA, one RSA with SHA-256, one RSA with SHA-1). An adequate certificate will be selected according to the client’s advertised capabilities. In case multiple certificates are adequate, preference is given to the one set by the first call to this function, then second, etc.

Note

On client, only the first call has any effect. That is, only one client certificate can be provisioned. The server’s preferences in its CertificateRequest message will be ignored and our only cert will be sent regardless of whether it matches those preferences - the server can then decide what it wants to do with it.

Note

The provided pk_key needs to match the public key in the first certificate in own_cert, or all handshakes using that certificate will fail. It is your responsibility to ensure that; this function will not perform any check. You may use mbedtls_pk_check_pair() in order to perform this check yourself, but be aware that this function can be computationally expensive on some key types.

Parameters:

conf – SSL configuration
own_cert – own public certificate chain
pk_key – own private key

Returns:

0 on success or MBEDTLS_ERR_SSL_ALLOC_FAILED

int mbedtls_ssl_conf_psk(mbedtls_ssl_config *conf, const unsigned char *psk, size_t psk_len, const unsigned char *psk_identity, size_t psk_identity_len)

Configure a pre-shared key (PSK) and identity to be used in PSK-based ciphersuites.

Note

This is mainly useful for clients. Servers will usually want to use mbedtls_ssl_conf_psk_cb() instead.

Note

A PSK set by mbedtls_ssl_set_hs_psk() in the PSK callback takes precedence over a PSK configured by this function.

Note

The PSK and its identity are copied internally and hence need not be preserved by the caller for the lifetime of the SSL configuration.

Warning

Currently, clients can only register a single pre-shared key. Calling this function or mbedtls_ssl_conf_psk_opaque() more than once will overwrite values configured in previous calls. Support for setting multiple PSKs on clients and selecting one based on the identity hint is not a planned feature, but feedback is welcomed.

Parameters:

conf – The SSL configuration to register the PSK with.
psk – The pointer to the pre-shared key to use.
psk_len – The length of the pre-shared key in bytes.
psk_identity – The pointer to the pre-shared key identity.
psk_identity_len – The length of the pre-shared key identity in bytes.

Returns:

0 if successful.

Returns:

An MBEDTLS_ERR_SSL_XXX error code on failure.

int mbedtls_ssl_conf_psk_opaque(mbedtls_ssl_config *conf, psa_key_id_t psk, const unsigned char *psk_identity, size_t psk_identity_len)

Configure an opaque pre-shared key (PSK) and identity to be used in PSK-based ciphersuites.

Note

This is mainly useful for clients. Servers will usually want to use mbedtls_ssl_conf_psk_cb() instead.

Note

An opaque PSK set by mbedtls_ssl_set_hs_psk_opaque() in the PSK callback takes precedence over an opaque PSK configured by this function.

Note

The PSK identity hint is copied internally and hence need not be preserved by the caller for the lifetime of the SSL configuration.

Warning

Currently, clients can only register a single pre-shared key. Calling this function or mbedtls_ssl_conf_psk() more than once will overwrite values configured in previous calls. Support for setting multiple PSKs on clients and selecting one based on the identity hint is not a planned feature, but feedback is welcomed.

Parameters:

conf – The SSL configuration to register the PSK with.
psk – The identifier of the key slot holding the PSK. Until conf is destroyed or this function is successfully called again, the key slot psk must be populated with a key of type PSA_ALG_CATEGORY_KEY_DERIVATION whose policy allows its use for the key derivation algorithm applied in the handshake.
psk_identity – The pointer to the pre-shared key identity.
psk_identity_len – The length of the pre-shared key identity in bytes.

Returns:

0 if successful.

Returns:

An MBEDTLS_ERR_SSL_XXX error code on failure.

int mbedtls_ssl_set_hs_psk(mbedtls_ssl_context *ssl, const unsigned char *psk, size_t psk_len)

Set the pre-shared Key (PSK) for the current handshake.

Note

This should only be called inside the PSK callback, i.e. the function passed to mbedtls_ssl_conf_psk_cb().

Note

A PSK set by this function takes precedence over a PSK configured by mbedtls_ssl_conf_psk().

Parameters:

ssl – The SSL context to configure a PSK for.
psk – The pointer to the pre-shared key.
psk_len – The length of the pre-shared key in bytes.

Returns:

0 if successful.

Returns:

An MBEDTLS_ERR_SSL_XXX error code on failure.

int mbedtls_ssl_set_hs_psk_opaque(mbedtls_ssl_context *ssl, psa_key_id_t psk)

Set an opaque pre-shared Key (PSK) for the current handshake.

Note

This should only be called inside the PSK callback, i.e. the function passed to mbedtls_ssl_conf_psk_cb().

Note

An opaque PSK set by this function takes precedence over an opaque PSK configured by mbedtls_ssl_conf_psk_opaque().

Parameters:

ssl – The SSL context to configure a PSK for.
psk – The identifier of the key slot holding the PSK. For the duration of the current handshake, the key slot must be populated with a key of type PSA_ALG_CATEGORY_KEY_DERIVATION whose policy allows its use for the key derivation algorithm applied in the handshake.

Returns:

0 if successful.

Returns:

An MBEDTLS_ERR_SSL_XXX error code on failure.

void mbedtls_ssl_conf_psk_cb(mbedtls_ssl_config *conf, int (*f_psk)(void*, mbedtls_ssl_context*, const unsigned char*, size_t), void *p_psk)

Set the PSK callback (server-side only).

            If set, the PSK callback is called for each
            handshake where a PSK-based ciphersuite was negotiated.
            The caller provides the identity received and wants to
            receive the actual PSK data and length.

            The callback has the following parameters:
            - \c void*: The opaque pointer \p p_psk.
            - \c mbedtls_ssl_context*: The SSL context to which
                                       the operation applies.
            - \c const unsigned char*: The PSK identity
                                       selected by the client.
            - \c size_t: The length of the PSK identity
                         selected by the client.

            If a valid PSK identity is found, the callback should use
            \c mbedtls_ssl_set_hs_psk() or
            \c mbedtls_ssl_set_hs_psk_opaque()
            on the SSL context to set the correct PSK and return \c 0.
            Any other return value will result in a denied PSK identity.

Note

A dynamic PSK (i.e. set by the PSK callback) takes precedence over a static PSK (i.e. set by mbedtls_ssl_conf_psk() or mbedtls_ssl_conf_psk_opaque()). This means that if you set a PSK callback using this function, you don’t need to set a PSK using mbedtls_ssl_conf_psk() or mbedtls_ssl_conf_psk_opaque()).

Parameters:

conf – The SSL configuration to register the callback with.
f_psk – The callback for selecting and setting the PSK based in the PSK identity chosen by the client.
p_psk – A pointer to an opaque structure to be passed to the callback, for example a PSK store.

int mbedtls_ssl_conf_dh_param_bin(mbedtls_ssl_config *conf, const unsigned char *dhm_P, size_t P_len, const unsigned char *dhm_G, size_t G_len)

Set the Diffie-Hellman public P and G values from big-endian binary presentations. (Default values: MBEDTLS_DHM_RFC3526_MODP_2048_[PG]_BIN)

Parameters:

conf – SSL configuration
dhm_P – Diffie-Hellman-Merkle modulus in big-endian binary form
P_len – Length of DHM modulus
dhm_G – Diffie-Hellman-Merkle generator in big-endian binary form
G_len – Length of DHM generator

Returns:

0 if successful

int mbedtls_ssl_conf_dh_param_ctx(mbedtls_ssl_config *conf, mbedtls_dhm_context *dhm_ctx)

Set the Diffie-Hellman public P and G values, read from existing context (server-side only)

Parameters:

conf – SSL configuration
dhm_ctx – Diffie-Hellman-Merkle context

Returns:

0 if successful

void mbedtls_ssl_conf_dhm_min_bitlen(mbedtls_ssl_config *conf, unsigned int bitlen)

Set the minimum length for Diffie-Hellman parameters. (Client-side only.) (Default: 1024 bits.)

Parameters:

conf – SSL configuration
bitlen – Minimum bit length of the DHM prime

void mbedtls_ssl_conf_curves(mbedtls_ssl_config *conf, const mbedtls_ecp_group_id *curves)

Set the allowed curves in order of preference. (Default: all defined curves in order of decreasing size, except that Montgomery curves come last. This order is likely to change in a future version.)

On server: this only affects selection of the ECDHE curve; the curves used for ECDH and ECDSA are determined by the list of available certificates instead.

On client: this affects the list of curves offered for any use. The server can override our preference order.

Both sides: limits the set of curves accepted for use in ECDHE and in the peer’s end-entity certificate.

Note

This has no influence on which curves are allowed inside the certificate chains, see mbedtls_ssl_conf_cert_profile() for that. For the end-entity certificate however, the key will be accepted only if it is allowed both by this list and by the cert profile.

Note

This list should be ordered by decreasing preference (preferred curve first).

Parameters:

conf – SSL configuration
curves – Ordered list of allowed curves, terminated by MBEDTLS_ECP_DP_NONE.

void mbedtls_ssl_conf_sig_hashes(mbedtls_ssl_config *conf, const int *hashes)

Set the allowed hashes for signatures during the handshake. (Default: all SHA-2 hashes, largest first. Also SHA-1 if the compile-time option MBEDTLS_TLS_DEFAULT_ALLOW_SHA1_IN_KEY_EXCHANGE is enabled.)

Note

This only affects which hashes are offered and can be used for signatures during the handshake. Hashes for message authentication and the TLS PRF are controlled by the ciphersuite, see mbedtls_ssl_conf_ciphersuites(). Hashes used for certificate signature are controlled by the verification profile, see mbedtls_ssl_conf_cert_profile().

Note

This list should be ordered by decreasing preference (preferred hash first).

Parameters:

conf – SSL configuration
hashes – Ordered list of allowed signature hashes, terminated by MBEDTLS_MD_NONE.

int mbedtls_ssl_set_hostname(mbedtls_ssl_context *ssl, const char *hostname)

Set or reset the hostname to check against the received peer certificate. On a client, this also sets the ServerName TLS extension, if that extension is enabled. On a TLS 1.3 client, this also sets the server name in the session resumption ticket, if that feature is enabled.

Hostname set to the one provided on success (cleared when NULL). On allocation failure hostname is cleared. On too long input failure, old hostname is unchanged.

Note

Maximum hostname length MBEDTLS_SSL_MAX_HOST_NAME_LEN.

Note

If the hostname is NULL on a client, then the server is not authenticated: it only needs to have a valid certificate, not a certificate matching its name. Therefore you should always call this function on a client, unless the connection is set up to only allow pre-shared keys, or in scenarios where server impersonation is not a concern. See the documentation of MBEDTLS_ERR_SSL_CERTIFICATE_VERIFICATION_WITHOUT_HOSTNAME for more details.

Parameters:

ssl – SSL context
hostname – The server hostname. This may be NULL to clear the hostname.

Returns:

0 if successful, MBEDTLS_ERR_SSL_ALLOC_FAILED on allocation failure, MBEDTLS_ERR_SSL_BAD_INPUT_DATA on too long input hostname.

int mbedtls_ssl_set_hs_own_cert(mbedtls_ssl_context *ssl, mbedtls_x509_crt *own_cert, mbedtls_pk_context *pk_key)

Set own certificate and key for the current handshake.

Note

Same as mbedtls_ssl_conf_own_cert() but for use within the SNI callback.

Parameters:

ssl – SSL context
own_cert – own public certificate chain
pk_key – own private key

Returns:

0 on success or MBEDTLS_ERR_SSL_ALLOC_FAILED

void mbedtls_ssl_set_hs_ca_chain(mbedtls_ssl_context *ssl, mbedtls_x509_crt *ca_chain, mbedtls_x509_crl *ca_crl)

Set the data required to verify peer certificate for the current handshake.

Note

Same as mbedtls_ssl_conf_ca_chain() but for use within the SNI callback.

Parameters:

ssl – SSL context
ca_chain – trusted CA chain (meaning all fully trusted top-level CAs)
ca_crl – trusted CA CRLs

void mbedtls_ssl_set_hs_authmode(mbedtls_ssl_context *ssl, int authmode)

Set authmode for the current handshake.

Note

Same as mbedtls_ssl_conf_authmode() but for use within the SNI callback.

Parameters:

ssl – SSL context
authmode – MBEDTLS_SSL_VERIFY_NONE, MBEDTLS_SSL_VERIFY_OPTIONAL or MBEDTLS_SSL_VERIFY_REQUIRED

void mbedtls_ssl_conf_sni(mbedtls_ssl_config *conf, int (*f_sni)(void*, mbedtls_ssl_context*, const unsigned char*, size_t), void *p_sni)

Set server side ServerName TLS extension callback (optional, server-side only).

If set, the ServerName callback is called whenever the server receives a ServerName TLS extension from the client during a handshake. The ServerName callback has the following parameters: (void *parameter, mbedtls_ssl_context *ssl, const unsigned char *hostname, size_t len). If a suitable certificate is found, the callback must set the certificate(s) and key(s) to use with mbedtls_ssl_set_hs_own_cert() (can be called repeatedly), and may optionally adjust the CA and associated CRL with mbedtls_ssl_set_hs_ca_chain() as well as the client authentication mode with mbedtls_ssl_set_hs_authmode(), then must return 0. If no matching name is found, the callback must either set a default cert, or return non-zero to abort the handshake at this point.

Parameters:

conf – SSL configuration
f_sni – verification function
p_sni – verification parameter

int mbedtls_ssl_set_hs_ecjpake_password(mbedtls_ssl_context *ssl, const unsigned char *pw, size_t pw_len)

Set the EC J-PAKE password for current handshake.

Note

An internal copy is made, and destroyed as soon as the handshake is completed, or when the SSL context is reset or freed.

Note

The SSL context needs to be already set up. The right place to call this function is between mbedtls_ssl_setup() or mbedtls_ssl_reset() and mbedtls_ssl_handshake().

Parameters:

ssl – SSL context
pw – EC J-PAKE password (pre-shared secret)
pw_len – length of pw in bytes

Returns:

0 on success, or a negative error code.

int mbedtls_ssl_conf_alpn_protocols(mbedtls_ssl_config *conf, const char **protos)

Set the supported Application Layer Protocols.

Parameters:

conf – SSL configuration
protos – Pointer to a NULL-terminated list of supported protocols, in decreasing preference order. The pointer to the list is recorded by the library for later reference as required, so the lifetime of the table must be at least as long as the lifetime of the SSL configuration structure.

Returns:

0 on success, or MBEDTLS_ERR_SSL_BAD_INPUT_DATA.

const char *mbedtls_ssl_get_alpn_protocol(const mbedtls_ssl_context *ssl)

Get the name of the negotiated Application Layer Protocol. This function should be called after the handshake is completed.

Parameters:: ssl – SSL context
Returns:: Protocol name, or NULL if no protocol was negotiated.

static inline const char *mbedtls_ssl_get_srtp_profile_as_string(mbedtls_ssl_srtp_profile profile)

void mbedtls_ssl_conf_srtp_mki_value_supported(mbedtls_ssl_config *conf, int support_mki_value)

Manage support for mki(master key id) value in use_srtp extension. MKI is an optional part of SRTP used for key management and re-keying. See RFC3711 section 3.1 for details. The default value is MBEDTLS_SSL_DTLS_SRTP_MKI_UNSUPPORTED.

Parameters:

conf – The SSL configuration to manage mki support.
support_mki_value – Enable or disable mki usage. Values are MBEDTLS_SSL_DTLS_SRTP_MKI_UNSUPPORTED or MBEDTLS_SSL_DTLS_SRTP_MKI_SUPPORTED.

int mbedtls_ssl_conf_dtls_srtp_protection_profiles(mbedtls_ssl_config *conf, const mbedtls_ssl_srtp_profile *profiles)

Set the supported DTLS-SRTP protection profiles.

Parameters:

conf – SSL configuration
profiles – Pointer to a List of MBEDTLS_TLS_SRTP_UNSET terminated supported protection profiles in decreasing preference order. The pointer to the list is recorded by the library for later reference as required, so the lifetime of the table must be at least as long as the lifetime of the SSL configuration structure. The list must not hold more than MBEDTLS_TLS_SRTP_MAX_PROFILE_LIST_LENGTH elements (excluding the terminating MBEDTLS_TLS_SRTP_UNSET).

Returns:

0 on success

Returns:

MBEDTLS_ERR_SSL_BAD_INPUT_DATA when the list of protection profiles is incorrect.

int mbedtls_ssl_dtls_srtp_set_mki_value(mbedtls_ssl_context *ssl, unsigned char *mki_value, uint16_t mki_len)

Set the mki_value for the current DTLS-SRTP session.

Note

This function is relevant on client side only. The server discovers the mki value during handshake. A mki value set on server side using this function is ignored.

Parameters:

ssl – SSL context to use.
mki_value – The MKI value to set.
mki_len – The length of the MKI value.

Returns:

0 on success

Returns:

MBEDTLS_ERR_SSL_BAD_INPUT_DATA

Returns:

MBEDTLS_ERR_SSL_FEATURE_UNAVAILABLE

void mbedtls_ssl_get_dtls_srtp_negotiation_result(const mbedtls_ssl_context *ssl, mbedtls_dtls_srtp_info *dtls_srtp_info)

Get the negotiated DTLS-SRTP information: Protection profile and MKI value.

Warning

This function must be called after the handshake is completed. The value returned by this function must not be trusted or acted upon before the handshake completes.

Parameters:

ssl – The SSL context to query.
dtls_srtp_info – The negotiated DTLS-SRTP information:
- Protection profile in use. A direct mapping of the iana defined value for protection profile on an uint16_t. http://www.iana.org/assignments/srtp-protection/srtp-protection.xhtml MBEDTLS_TLS_SRTP_UNSET if the use of SRTP was not negotiated or peer’s Hello packet was not parsed yet.
- mki size and value( if size is > 0 ).

void mbedtls_ssl_conf_max_version(mbedtls_ssl_config *conf, int major, int minor)

Set the maximum supported version sent from the client side and/or accepted at the server side (Default: MBEDTLS_SSL_MAX_MAJOR_VERSION, MBEDTLS_SSL_MAX_MINOR_VERSION)

Note

This ignores ciphersuites from higher versions.

Note

With DTLS, use MBEDTLS_SSL_MINOR_VERSION_2 for DTLS 1.0 and MBEDTLS_SSL_MINOR_VERSION_3 for DTLS 1.2

Parameters:

conf – SSL configuration
major – Major version number (only MBEDTLS_SSL_MAJOR_VERSION_3 supported)
minor – Minor version number (MBEDTLS_SSL_MINOR_VERSION_0, MBEDTLS_SSL_MINOR_VERSION_1 and MBEDTLS_SSL_MINOR_VERSION_2, MBEDTLS_SSL_MINOR_VERSION_3 supported)

void mbedtls_ssl_conf_min_version(mbedtls_ssl_config *conf, int major, int minor)

Set the minimum accepted SSL/TLS protocol version (Default: TLS 1.0)

Note

Input outside of the SSL_MAX_XXXXX_VERSION and SSL_MIN_XXXXX_VERSION range is ignored.

Note

MBEDTLS_SSL_MINOR_VERSION_0 (SSL v3) should be avoided.

Note

With DTLS, use MBEDTLS_SSL_MINOR_VERSION_2 for DTLS 1.0 and MBEDTLS_SSL_MINOR_VERSION_3 for DTLS 1.2

Parameters:

conf – SSL configuration
major – Major version number (only MBEDTLS_SSL_MAJOR_VERSION_3 supported)
minor – Minor version number (MBEDTLS_SSL_MINOR_VERSION_0, MBEDTLS_SSL_MINOR_VERSION_1 and MBEDTLS_SSL_MINOR_VERSION_2, MBEDTLS_SSL_MINOR_VERSION_3 supported)

void mbedtls_ssl_conf_fallback(mbedtls_ssl_config *conf, char fallback)

Set the fallback flag (client-side only). (Default: MBEDTLS_SSL_IS_NOT_FALLBACK).

Note

Set to MBEDTLS_SSL_IS_FALLBACK when preparing a fallback connection, that is a connection with max_version set to a lower value than the value you’re willing to use. Such fallback connections are not recommended but are sometimes necessary to interoperate with buggy (version-intolerant) servers.

Warning

You should NOT set this to MBEDTLS_SSL_IS_FALLBACK for non-fallback connections! This would appear to work for a while, then cause failures when the server is upgraded to support a newer TLS version.

Parameters:

conf – SSL configuration
fallback – MBEDTLS_SSL_IS_NOT_FALLBACK or MBEDTLS_SSL_IS_FALLBACK

void mbedtls_ssl_conf_encrypt_then_mac(mbedtls_ssl_config *conf, char etm)

Enable or disable Encrypt-then-MAC (Default: MBEDTLS_SSL_ETM_ENABLED)

Note

This should always be enabled, it is a security improvement, and should not cause any interoperability issue (used only if the peer supports it too).

Parameters:

conf – SSL configuration
etm – MBEDTLS_SSL_ETM_ENABLED or MBEDTLS_SSL_ETM_DISABLED

void mbedtls_ssl_conf_extended_master_secret(mbedtls_ssl_config *conf, char ems)

Enable or disable Extended Master Secret negotiation. (Default: MBEDTLS_SSL_EXTENDED_MS_ENABLED)

Note

This should always be enabled, it is a security fix to the protocol, and should not cause any interoperability issue (used only if the peer supports it too).

Parameters:

conf – SSL configuration
ems – MBEDTLS_SSL_EXTENDED_MS_ENABLED or MBEDTLS_SSL_EXTENDED_MS_DISABLED

void mbedtls_ssl_conf_arc4_support(mbedtls_ssl_config *conf, char arc4)

Disable or enable support for RC4 (Default: MBEDTLS_SSL_ARC4_DISABLED)

Note

This function is deprecated and will be removed in a future version of the library. RC4 is disabled by default at compile time and needs to be actively enabled for use with legacy systems.

Warning

Use of RC4 in DTLS/TLS has been prohibited by RFC 7465 for security reasons. Use at your own risk.

Parameters:

conf – SSL configuration
arc4 – MBEDTLS_SSL_ARC4_ENABLED or MBEDTLS_SSL_ARC4_DISABLED

void mbedtls_ssl_conf_cert_req_ca_list(mbedtls_ssl_config *conf, char cert_req_ca_list)

Whether to send a list of acceptable CAs in CertificateRequest messages. (Default: do send)

Parameters:

conf – SSL configuration
cert_req_ca_list – MBEDTLS_SSL_CERT_REQ_CA_LIST_ENABLED or MBEDTLS_SSL_CERT_REQ_CA_LIST_DISABLED

int mbedtls_ssl_conf_max_frag_len(mbedtls_ssl_config *conf, unsigned char mfl_code)

Set the maximum fragment length to emit and/or negotiate. (Typical: the smaller of MBEDTLS_SSL_IN_CONTENT_LEN and MBEDTLS_SSL_OUT_CONTENT_LEN, usually 2^14 bytes) (Server: set maximum fragment length to emit, usually negotiated by the client during handshake) (Client: set maximum fragment length to emit and negotiate with the server during handshake) (Default: MBEDTLS_SSL_MAX_FRAG_LEN_NONE)

Note

On the client side, the maximum fragment length extension will not be used, unless the maximum fragment length has been set via this function to a value different than MBEDTLS_SSL_MAX_FRAG_LEN_NONE.

Note

With TLS, this currently only affects ApplicationData (sent with mbedtls_ssl_read()), not handshake messages. With DTLS, this affects both ApplicationData and handshake.

Note

This sets the maximum length for a record’s payload, excluding record overhead that will be added to it, see mbedtls_ssl_get_record_expansion().

Note

For DTLS, it is also possible to set a limit for the total size of datagrams passed to the transport layer, including record overhead, see mbedtls_ssl_set_mtu().

Parameters:

conf – SSL configuration
mfl_code – Code for maximum fragment length (allowed values: MBEDTLS_SSL_MAX_FRAG_LEN_512, MBEDTLS_SSL_MAX_FRAG_LEN_1024, MBEDTLS_SSL_MAX_FRAG_LEN_2048, MBEDTLS_SSL_MAX_FRAG_LEN_4096)

Returns:

0 if successful or MBEDTLS_ERR_SSL_BAD_INPUT_DATA

void mbedtls_ssl_conf_truncated_hmac(mbedtls_ssl_config *conf, int truncate)

Activate negotiation of truncated HMAC (Default: MBEDTLS_SSL_TRUNC_HMAC_DISABLED)

Parameters:

conf – SSL configuration
truncate – Enable or disable (MBEDTLS_SSL_TRUNC_HMAC_ENABLED or MBEDTLS_SSL_TRUNC_HMAC_DISABLED)

void mbedtls_ssl_conf_cbc_record_splitting(mbedtls_ssl_config *conf, char split)

Enable / Disable 1/n-1 record splitting (Default: MBEDTLS_SSL_CBC_RECORD_SPLITTING_ENABLED)

Note

Only affects SSLv3 and TLS 1.0, not higher versions. Does not affect non-CBC ciphersuites in any version.

Parameters:

conf – SSL configuration
split – MBEDTLS_SSL_CBC_RECORD_SPLITTING_ENABLED or MBEDTLS_SSL_CBC_RECORD_SPLITTING_DISABLED

void mbedtls_ssl_conf_session_tickets(mbedtls_ssl_config *conf, int use_tickets)

Enable / Disable session tickets (client only). (Default: MBEDTLS_SSL_SESSION_TICKETS_ENABLED.)

Note

On server, use mbedtls_ssl_conf_session_tickets_cb().

Parameters:

conf – SSL configuration
use_tickets – Enable or disable (MBEDTLS_SSL_SESSION_TICKETS_ENABLED or MBEDTLS_SSL_SESSION_TICKETS_DISABLED)

void mbedtls_ssl_conf_renegotiation(mbedtls_ssl_config *conf, int renegotiation)

Enable / Disable renegotiation support for connection when initiated by peer (Default: MBEDTLS_SSL_RENEGOTIATION_DISABLED)

Note

Server-side, enabling renegotiation also makes the server susceptible to a resource DoS by a malicious client.

Warning

It is recommended to always disable renegotiation unless you know you need it and you know what you’re doing. In the past, there have been several issues associated with renegotiation or a poor understanding of its properties.

Parameters:

conf – SSL configuration
renegotiation – Enable or disable (MBEDTLS_SSL_RENEGOTIATION_ENABLED or MBEDTLS_SSL_RENEGOTIATION_DISABLED)

void mbedtls_ssl_conf_legacy_renegotiation(mbedtls_ssl_config *conf, int allow_legacy)

Prevent or allow legacy renegotiation. (Default: MBEDTLS_SSL_LEGACY_NO_RENEGOTIATION)

MBEDTLS_SSL_LEGACY_NO_RENEGOTIATION allows connections to be established even if the peer does not support secure renegotiation, but does not allow renegotiation to take place if not secure. (Interoperable and secure option)

MBEDTLS_SSL_LEGACY_ALLOW_RENEGOTIATION allows renegotiations with non-upgraded peers. Allowing legacy renegotiation makes the connection vulnerable to specific man in the middle attacks. (See RFC 5746) (Most interoperable and least secure option)

MBEDTLS_SSL_LEGACY_BREAK_HANDSHAKE breaks off connections if peer does not support secure renegotiation. Results in interoperability issues with non-upgraded peers that do not support renegotiation altogether. (Most secure option, interoperability issues)

Parameters:

conf – SSL configuration
allow_legacy – Prevent or allow (SSL_NO_LEGACY_RENEGOTIATION, SSL_ALLOW_LEGACY_RENEGOTIATION or MBEDTLS_SSL_LEGACY_BREAK_HANDSHAKE)

void mbedtls_ssl_conf_renegotiation_enforced(mbedtls_ssl_config *conf, int max_records)

Enforce renegotiation requests. (Default: enforced, max_records = 16)

When we request a renegotiation, the peer can comply or ignore the request. This function allows us to decide whether to enforce our renegotiation requests by closing the connection if the peer doesn’t comply.

However, records could already be in transit from the peer when the request is emitted. In order to increase reliability, we can accept a number of records before the expected handshake records.

The optimal value is highly dependent on the specific usage scenario.

Note

With DTLS and server-initiated renegotiation, the HelloRequest is retransmitted every time mbedtls_ssl_read() times out or receives Application Data, until:

max_records records have beens seen, if it is >= 0, or
the number of retransmits that would happen during an actual handshake has been reached. Please remember the request might be lost a few times if you consider setting max_records to a really low value.

Warning

On client, the grace period can only happen during mbedtls_ssl_read(), as opposed to mbedtls_ssl_write() and mbedtls_ssl_renegotiate() which always behave as if max_record was 0. The reason is, if we receive application data from the server, we need a place to write it, which only happens during mbedtls_ssl_read().

Parameters:

conf – SSL configuration
max_records – Use MBEDTLS_SSL_RENEGOTIATION_NOT_ENFORCED if you don’t want to enforce renegotiation, or a non-negative value to enforce it but allow for a grace period of max_records records.

void mbedtls_ssl_conf_renegotiation_period(mbedtls_ssl_config *conf, const unsigned char period[8])

Set record counter threshold for periodic renegotiation. (Default: 2^48 - 1)

Renegotiation is automatically triggered when a record counter (outgoing or incoming) crosses the defined threshold. The default value is meant to prevent the connection from being closed when the counter is about to reached its maximal value (it is not allowed to wrap).

Lower values can be used to enforce policies such as “keys

must be refreshed every N packets with cipher X”.

The renegotiation period can be disabled by setting conf->disable_renegotiation to MBEDTLS_SSL_RENEGOTIATION_DISABLED.

Note

When the configured transport is MBEDTLS_SSL_TRANSPORT_DATAGRAM the maximum renegotiation period is 2^48 - 1, and for MBEDTLS_SSL_TRANSPORT_STREAM, the maximum renegotiation period is 2^64 - 1.

Parameters:

conf – SSL configuration
period – The threshold value: a big-endian 64-bit number.

int mbedtls_ssl_check_pending(const mbedtls_ssl_context *ssl)

Check if there is data already read from the underlying transport but not yet processed.

Note

This is different in purpose and behaviour from mbedtls_ssl_get_bytes_avail in that it considers any kind of unprocessed data, not only unread application data. If mbedtls_ssl_get_bytes returns a non-zero value, this function will also signal pending data, but the converse does not hold. For example, in DTLS there might be further records waiting to be processed from the current underlying transport’s datagram.

Note

If this function returns 1 (data pending), this does not imply that a subsequent call to mbedtls_ssl_read will provide any data; e.g., the unprocessed data might turn out to be an alert or a handshake message.

Note

This function is useful in the following situation: If the SSL/TLS module successfully returns from an operation - e.g. a handshake or an application record read - and you’re awaiting incoming data next, you must not immediately idle on the underlying transport to have data ready, but you need to check the value of this function first. The reason is that the desired data might already be read but not yet processed. If, in contrast, a previous call to the SSL/TLS module returned MBEDTLS_ERR_SSL_WANT_READ, it is not necessary to call this function, as the latter error code entails that all internal data has been processed.

Parameters:: ssl – SSL context
Returns:: 0 if nothing’s pending, 1 otherwise.

size_t mbedtls_ssl_get_bytes_avail(const mbedtls_ssl_context *ssl)

Return the number of application data bytes remaining to be read from the current record.

Note

When working over a datagram transport, this is useful to detect the current datagram’s boundary in case mbedtls_ssl_read has written the maximal amount of data fitting into the input buffer.

Parameters:: ssl – SSL context
Returns:: How many bytes are available in the application data record read buffer.

uint32_t mbedtls_ssl_get_verify_result(const mbedtls_ssl_context *ssl)

Return the result of the certificate verification.

Parameters:: ssl – The SSL context to use.
Returns:: 0 if the certificate verification was successful.
Returns:: -1u if the result is not available. This may happen e.g. if the handshake aborts early, or a verification callback returned a fatal error.
Returns:: A bitwise combination of MBEDTLS_X509_BADCERT_XXX and MBEDTLS_X509_BADCRL_XXX failure flags; see x509.h.

const char *mbedtls_ssl_get_ciphersuite(const mbedtls_ssl_context *ssl)

Return the name of the current ciphersuite.

Parameters:: ssl – SSL context
Returns:: a string containing the ciphersuite name

const char *mbedtls_ssl_get_version(const mbedtls_ssl_context *ssl)

Return the current SSL version (SSLv3/TLSv1/etc)

Parameters:: ssl – SSL context
Returns:: a string containing the SSL version

int mbedtls_ssl_get_record_expansion(const mbedtls_ssl_context *ssl)

Return the (maximum) number of bytes added by the record layer: header + encryption/MAC overhead (inc. padding)

Note

This function is not available (always returns an error) when record compression is enabled.

Parameters:: ssl – SSL context
Returns:: Current maximum record expansion in bytes, or MBEDTLS_ERR_SSL_FEATURE_UNAVAILABLE if compression is enabled, which makes expansion much less predictable

size_t mbedtls_ssl_get_output_max_frag_len(const mbedtls_ssl_context *ssl)

Return the maximum fragment length (payload, in bytes) for the output buffer. For the client, this is the configured value. For the server, it is the minimum of two - the configured value and the negotiated one.

See also

mbedtls_ssl_conf_max_frag_len()

See also

mbedtls_ssl_get_max_record_payload()

Parameters:: ssl – SSL context
Returns:: Current maximum fragment length for the output buffer.

size_t mbedtls_ssl_get_input_max_frag_len(const mbedtls_ssl_context *ssl)

Return the maximum fragment length (payload, in bytes) for the input buffer. This is the negotiated maximum fragment length, or, if there is none, MBEDTLS_SSL_MAX_CONTENT_LEN. If it is not defined either, the value is 2^14. This function works as its predecessor, mbedtls_ssl_get_max_frag_len().

See also

mbedtls_ssl_conf_max_frag_len()

See also

mbedtls_ssl_get_max_record_payload()

Parameters:: ssl – SSL context
Returns:: Current maximum fragment length for the output buffer.

int mbedtls_ssl_get_max_out_record_payload(const mbedtls_ssl_context *ssl)

Return the current maximum outgoing record payload in bytes. This takes into account the config.h setting MBEDTLS_SSL_OUT_CONTENT_LEN, the configured and negotiated max fragment length extension if used, and for DTLS the path MTU as configured and current record expansion.

See also

mbedtls_ssl_set_mtu()

See also

mbedtls_ssl_get_output_max_frag_len()

See also

mbedtls_ssl_get_input_max_frag_len()

See also

mbedtls_ssl_get_record_expansion()

Note

With DTLS, mbedtls_ssl_write() will return an error if called with a larger length value. With TLS, mbedtls_ssl_write() will fragment the input if necessary and return the number of bytes written; it is up to the caller to call mbedtls_ssl_write() again in order to send the remaining bytes if any.

Note

This function is not available (always returns an error) when record compression is enabled.

Parameters:: ssl – SSL context
Returns:: Current maximum payload for an outgoing record, or a negative error code.

const mbedtls_x509_crt *mbedtls_ssl_get_peer_cert(const mbedtls_ssl_context *ssl)

Return the peer certificate from the current connection.

Note

For one-time inspection of the peer’s certificate during the handshake, consider registering an X.509 CRT verification callback through mbedtls_ssl_conf_verify() instead of calling this function. Using mbedtls_ssl_conf_verify() also comes at the benefit of allowing you to influence the verification process, for example by masking expected and tolerated verification failures.

Warning

You must not use the pointer returned by this function after any further call to the SSL API, including mbedtls_ssl_read() and mbedtls_ssl_write(); this is because the pointer might change during renegotiation, which happens transparently to the user. If you want to use the certificate across API calls, you must make a copy.

Parameters:: ssl – The SSL context to use. This must be initialized and setup.
Returns:: The current peer certificate, if available. The returned certificate is owned by the SSL context and is valid only until the next call to the SSL API.
Returns:: NULL if no peer certificate is available. This might be because the chosen ciphersuite doesn’t use CRTs (PSK-based ciphersuites, for example), or because MBEDTLS_SSL_KEEP_PEER_CERTIFICATE has been disabled, allowing the stack to free the peer’s CRT to save memory.

int mbedtls_ssl_get_session(const mbedtls_ssl_context *ssl, mbedtls_ssl_session *session)

Save session in order to resume it later (client-side only) Session data is copied to presented session structure.

See also

mbedtls_ssl_set_session()

Note

Only the server certificate is copied, and not the full chain, so you should not attempt to validate the certificate again by calling mbedtls_x509_crt_verify() on it. Instead, you should use the results from the verification in the original handshake by calling mbedtls_ssl_get_verify_result() after loading the session again into a new SSL context using mbedtls_ssl_set_session().

Note

Once the session object is not needed anymore, you should free it by calling mbedtls_ssl_session_free().

Parameters:

ssl – SSL context
session – session context

Returns:

0 if successful, MBEDTLS_ERR_SSL_ALLOC_FAILED if memory allocation failed, MBEDTLS_ERR_SSL_BAD_INPUT_DATA if used server-side or arguments are otherwise invalid.

int mbedtls_ssl_handshake(mbedtls_ssl_context *ssl)

Perform the SSL handshake.

Note

If DTLS is in use, then you may choose to handle MBEDTLS_ERR_SSL_HELLO_VERIFY_REQUIRED specially for logging purposes, as it is an expected return value rather than an actual error, but you still need to reset/free the context.

Note

Remarks regarding event-driven DTLS: If the function returns MBEDTLS_ERR_SSL_WANT_READ, no datagram from the underlying transport layer is currently being processed, and it is safe to idle until the timer or the underlying transport signal a new event. This is not true for a successful handshake, in which case the datagram of the underlying transport that is currently being processed might or might not contain further DTLS records.

Note

If MBEDTLS_USE_PSA_CRYPTO is enabled, the PSA crypto subsystem must have been initialized by calling psa_crypto_init() before calling this function.

Warning

If this function returns something other than 0, MBEDTLS_ERR_SSL_WANT_READ, MBEDTLS_ERR_SSL_WANT_WRITE, MBEDTLS_ERR_SSL_ASYNC_IN_PROGRESS or MBEDTLS_ERR_SSL_CRYPTO_IN_PROGRESS, you must stop using the SSL context for reading or writing, and either free it or call mbedtls_ssl_session_reset() on it before re-using it for a new connection; the current connection must be closed.

Parameters:: ssl – SSL context
Returns:: 0 if successful.
Returns:: MBEDTLS_ERR_SSL_WANT_READ or MBEDTLS_ERR_SSL_WANT_WRITE if the handshake is incomplete and waiting for data to be available for reading from or writing to the underlying transport - in this case you must call this function again when the underlying transport is ready for the operation.
Returns:: MBEDTLS_ERR_SSL_ASYNC_IN_PROGRESS if an asynchronous operation is in progress (see mbedtls_ssl_conf_async_private_cb()) - in this case you must call this function again when the operation is ready.
Returns:: MBEDTLS_ERR_SSL_CRYPTO_IN_PROGRESS if a cryptographic operation is in progress (see mbedtls_ecp_set_max_ops()) - in this case you must call this function again to complete the handshake when you’re done attending other tasks.
Returns:: MBEDTLS_ERR_SSL_HELLO_VERIFY_REQUIRED if DTLS is in use and the client did not demonstrate reachability yet - in this case you must stop using the context (see below).
Returns:: Another SSL error code - in this case you must stop using the context (see below).

int mbedtls_ssl_handshake_step(mbedtls_ssl_context *ssl)

Perform a single step of the SSL handshake.

Note

The state of the context (ssl->state) will be at the next state after this function returns 0. Do not call this function if state is MBEDTLS_SSL_HANDSHAKE_OVER.

Warning

If this function returns something other than 0, MBEDTLS_ERR_SSL_WANT_READ, MBEDTLS_ERR_SSL_WANT_WRITE, MBEDTLS_ERR_SSL_ASYNC_IN_PROGRESS or MBEDTLS_ERR_SSL_CRYPTO_IN_PROGRESS, you must stop using the SSL context for reading or writing, and either free it or call mbedtls_ssl_session_reset() on it before re-using it for a new connection; the current connection must be closed.

Parameters:: ssl – SSL context
Returns:: See mbedtls_ssl_handshake().

int mbedtls_ssl_renegotiate(mbedtls_ssl_context *ssl)

Initiate an SSL renegotiation on the running connection. Client: perform the renegotiation right now. Server: request renegotiation, which will be performed during the next call to mbedtls_ssl_read() if honored by client.

Warning

If this function returns something other than 0, MBEDTLS_ERR_SSL_WANT_READ, MBEDTLS_ERR_SSL_WANT_WRITE, MBEDTLS_ERR_SSL_ASYNC_IN_PROGRESS or MBEDTLS_ERR_SSL_CRYPTO_IN_PROGRESS, you must stop using the SSL context for reading or writing, and either free it or call mbedtls_ssl_session_reset() on it before re-using it for a new connection; the current connection must be closed.

Parameters:: ssl – SSL context
Returns:: 0 if successful, or any mbedtls_ssl_handshake() return value except MBEDTLS_ERR_SSL_CLIENT_RECONNECT that can’t happen during a renegotiation.

int mbedtls_ssl_read(mbedtls_ssl_context *ssl, unsigned char *buf, size_t len)

Read at most ‘len’ application data bytes.

Note

When this function returns MBEDTLS_ERR_SSL_CLIENT_RECONNECT (which can only happen server-side), it means that a client is initiating a new connection using the same source port. You can either treat that as a connection close and wait for the client to resend a ClientHello, or directly continue with mbedtls_ssl_handshake() with the same context (as it has been reset internally). Either way, you must make sure this is seen by the application as a new connection: application state, if any, should be reset, and most importantly the identity of the client must be checked again. WARNING: not validating the identity of the client again, or not transmitting the new identity to the application layer, would allow authentication bypass!

Note

Remarks regarding event-driven DTLS:

If the function returns MBEDTLS_ERR_SSL_WANT_READ, no datagram from the underlying transport layer is currently being processed, and it is safe to idle until the timer or the underlying transport signal a new event.
This function may return MBEDTLS_ERR_SSL_WANT_READ even if data was initially available on the underlying transport, as this data may have been only e.g. duplicated messages or a renegotiation request. Therefore, you must be prepared to receive MBEDTLS_ERR_SSL_WANT_READ even when reacting to an incoming-data event from the underlying transport.
On success, the datagram of the underlying transport that is currently being processed may contain further DTLS records. You should call mbedtls_ssl_check_pending to check for remaining records.

Warning

If this function returns something other than a positive value, MBEDTLS_ERR_SSL_WANT_READ, MBEDTLS_ERR_SSL_WANT_WRITE, MBEDTLS_ERR_SSL_ASYNC_IN_PROGRESS, MBEDTLS_ERR_SSL_CRYPTO_IN_PROGRESS or MBEDTLS_ERR_SSL_CLIENT_RECONNECT, you must stop using the SSL context for reading or writing, and either free it or call mbedtls_ssl_session_reset() on it before re-using it for a new connection; the current connection must be closed.

Parameters:

ssl – SSL context
buf – buffer that will hold the data
len – maximum number of bytes to read

Returns:

The (positive) number of bytes read if successful.

Returns:

0 if the read end of the underlying transport was closed without sending a CloseNotify beforehand, which might happen because of various reasons (internal error of an underlying stack, non-conformant peer not sending a CloseNotify and such) - in this case you must stop using the context (see below).

Returns:

MBEDTLS_ERR_SSL_PEER_CLOSE_NOTIFY if the underlying transport is still functional, but the peer has acknowledged to not send anything anymore.

Returns:

MBEDTLS_ERR_SSL_WANT_READ or MBEDTLS_ERR_SSL_WANT_WRITE if the handshake is incomplete and waiting for data to be available for reading from or writing to the underlying transport - in this case you must call this function again when the underlying transport is ready for the operation.

Returns:

MBEDTLS_ERR_SSL_ASYNC_IN_PROGRESS if an asynchronous operation is in progress (see mbedtls_ssl_conf_async_private_cb()) - in this case you must call this function again when the operation is ready.

Returns:

MBEDTLS_ERR_SSL_CRYPTO_IN_PROGRESS if a cryptographic operation is in progress (see mbedtls_ecp_set_max_ops()) - in this case you must call this function again to complete the handshake when you’re done attending other tasks.

Returns:

MBEDTLS_ERR_SSL_CLIENT_RECONNECT if we’re at the server side of a DTLS connection and the client is initiating a new connection using the same source port. See below.

Returns:

Another SSL error code - in this case you must stop using the context (see below).

int mbedtls_ssl_write(mbedtls_ssl_context *ssl, const unsigned char *buf, size_t len)

Try to write exactly ‘len’ application data bytes.

Note

When this function returns MBEDTLS_ERR_SSL_WANT_WRITE/READ, it must be called later with the same arguments, until it returns a value greater that or equal to 0. When the function returns MBEDTLS_ERR_SSL_WANT_WRITE there may be some partial data in the output buffer, however this is not yet sent.

Note

If the requested length is greater than the maximum fragment length (either the built-in limit or the one set or negotiated with the peer), then:

with TLS, less bytes than requested are written.
with DTLS, MBEDTLS_ERR_SSL_BAD_INPUT_DATA is returned. mbedtls_ssl_get_output_max_frag_len() may be used to query the active maximum fragment length.

Note

Attempting to write 0 bytes will result in an empty TLS application record being sent.

Warning

This function will do partial writes in some cases. If the return value is non-negative but less than length, the function must be called again with updated arguments: buf + ret, len - ret (if ret is the return value) until it returns a value equal to the last ‘len’ argument.

Warning

If this function returns something other than a non-negative value, MBEDTLS_ERR_SSL_WANT_READ, MBEDTLS_ERR_SSL_WANT_WRITE, MBEDTLS_ERR_SSL_ASYNC_IN_PROGRESS or MBEDTLS_ERR_SSL_CRYPTO_IN_PROGRESS, you must stop using the SSL context for reading or writing, and either free it or call mbedtls_ssl_session_reset() on it before re-using it for a new connection; the current connection must be closed.

Parameters:

ssl – SSL context
buf – buffer holding the data
len – how many bytes must be written

Returns:

The (non-negative) number of bytes actually written if successful (may be less than len).

Returns:

MBEDTLS_ERR_SSL_WANT_READ or MBEDTLS_ERR_SSL_WANT_WRITE if the handshake is incomplete and waiting for data to be available for reading from or writing to the underlying transport - in this case you must call this function again when the underlying transport is ready for the operation.

Returns:

MBEDTLS_ERR_SSL_ASYNC_IN_PROGRESS if an asynchronous operation is in progress (see mbedtls_ssl_conf_async_private_cb()) - in this case you must call this function again when the operation is ready.

Returns:

MBEDTLS_ERR_SSL_CRYPTO_IN_PROGRESS if a cryptographic operation is in progress (see mbedtls_ecp_set_max_ops()) - in this case you must call this function again to complete the handshake when you’re done attending other tasks.

Returns:

Another SSL error code - in this case you must stop using the context (see below).

int mbedtls_ssl_send_alert_message(mbedtls_ssl_context *ssl, unsigned char level, unsigned char message)

Send an alert message.

Note

If this function returns something other than 0 or MBEDTLS_ERR_SSL_WANT_READ/WRITE, you must stop using the SSL context for reading or writing, and either free it or call mbedtls_ssl_session_reset() on it before re-using it for a new connection; the current connection must be closed.

Parameters:

ssl – SSL context
level – The alert level of the message (MBEDTLS_SSL_ALERT_LEVEL_WARNING or MBEDTLS_SSL_ALERT_LEVEL_FATAL)
message – The alert message (SSL_ALERT_MSG_*)

Returns:

0 if successful, or a specific SSL error code.

int mbedtls_ssl_close_notify(mbedtls_ssl_context *ssl)

Notify the peer that the connection is being closed.

Note

If this function returns something other than 0 or MBEDTLS_ERR_SSL_WANT_READ/WRITE, you must stop using the SSL context for reading or writing, and either free it or call mbedtls_ssl_session_reset() on it before re-using it for a new connection; the current connection must be closed.

Parameters:: ssl – SSL context
Returns:: 0 if successful, or a specific SSL error code.

void mbedtls_ssl_free(mbedtls_ssl_context *ssl)

Free referenced items in an SSL context and clear memory.

Parameters:: ssl – SSL context

int mbedtls_ssl_context_save(mbedtls_ssl_context *ssl, unsigned char *buf, size_t buf_len, size_t *olen)

Save an active connection as serialized data in a buffer. This allows the freeing or re-using of the SSL context while still picking up the connection later in a way that it entirely transparent to the peer.

See also

mbedtls_ssl_context_load()

Note

This feature is currently only available under certain conditions, see the documentation of the return value MBEDTLS_ERR_SSL_BAD_INPUT_DATA for details.

Note

When this function succeeds, it calls mbedtls_ssl_session_reset() on ssl which as a result is no longer associated with the connection that has been serialized. This avoids creating copies of the connection state. You’re then free to either re-use the context structure for a different connection, or call mbedtls_ssl_free() on it. See the documentation of mbedtls_ssl_session_reset() for more details.

Note

olen is updated to the correct value regardless of whether buf_len was large enough. This makes it possible to determine the necessary size by calling this function with buf set to NULL and buf_len to 0. However, the value of olen is only guaranteed to be correct when the function returns MBEDTLS_ERR_SSL_BUFFER_TOO_SMALL or 0. If the return value is different, then the value of olen is undefined.

Parameters:

ssl – The SSL context to save. On success, it is no longer associated with the connection that has been serialized.
buf – The buffer to write the serialized data to. It must be a writeable buffer of at least buf_len bytes, or may be NULL if buf_len is 0.
buf_len – The number of bytes available for writing in buf.
olen – The size in bytes of the data that has been or would have been written. It must point to a valid size_t.

Returns:

0 if successful.

Returns:

MBEDTLS_ERR_SSL_BUFFER_TOO_SMALL if buf is too small.

Returns:

MBEDTLS_ERR_SSL_ALLOC_FAILED if memory allocation failed while resetting the context.

Returns:

MBEDTLS_ERR_SSL_BAD_INPUT_DATA if a handshake is in progress, or there is pending data for reading or sending, or the connection does not use DTLS 1.2 with an AEAD ciphersuite, or renegotiation is enabled.

int mbedtls_ssl_context_load(mbedtls_ssl_context *ssl, const unsigned char *buf, size_t len)

Load serialized connection data to an SSL context.

See also

mbedtls_ssl_context_save()

Note

Before calling this function, the SSL context must be prepared in one of the two following ways. The first way is to take a context freshly initialised with mbedtls_ssl_init() and call mbedtls_ssl_setup() on it with the same mbedtls_ssl_config structure that was used in the original connection. The second way is to call mbedtls_ssl_session_reset() on a context that was previously prepared as above but used in the meantime. Either way, you must not use the context to perform a handshake between calling mbedtls_ssl_setup() or mbedtls_ssl_session_reset() and calling this function. You may however call other setter functions in that time frame as indicated in the note below.

Note

Before or after calling this function successfully, you also need to configure some connection-specific callbacks and settings before you can use the connection again (unless they were already set before calling mbedtls_ssl_session_reset() and the values are suitable for the present connection). Specifically, you want to call at least mbedtls_ssl_set_bio() and mbedtls_ssl_set_timer_cb(). All other SSL setter functions are not necessary to call, either because they’re only used in handshakes, or because the setting is already saved. You might choose to call them anyway, for example in order to share code between the cases of establishing a new connection and the case of loading an already-established connection.

Note

If you have new information about the path MTU, you want to call mbedtls_ssl_set_mtu() after calling this function, as otherwise this function would overwrite your newly-configured value with the value that was active when the context was saved.

Note

When this function returns an error code, it calls mbedtls_ssl_free() on ssl. In this case, you need to prepare the context with the usual sequence starting with a call to mbedtls_ssl_init() if you want to use it again.

Warning

The same serialized data must never be loaded into more that one context. In order to ensure that, after successfully loading serialized data to an SSL context, you should immediately destroy or invalidate all copies of the serialized data that was loaded. Loading the same data in more than one context would cause severe security failures including but not limited to loss of confidentiality.

Parameters:

ssl – The SSL context structure to be populated. It must have been prepared as described in the note above.
buf – The buffer holding the serialized connection data. It must be a readable buffer of at least len bytes.
len – The size of the serialized data in bytes.

Returns:

0 if successful.

Returns:

MBEDTLS_ERR_SSL_ALLOC_FAILED if memory allocation failed.

Returns:

MBEDTLS_ERR_SSL_VERSION_MISMATCH if the serialized data comes from a different Mbed TLS version or build.

Returns:

MBEDTLS_ERR_SSL_BAD_INPUT_DATA if input data is invalid.

void mbedtls_ssl_config_init(mbedtls_ssl_config *conf)

Initialize an SSL configuration context Just makes the context ready for mbedtls_ssl_config_defaults() or mbedtls_ssl_config_free().

Note

You need to call mbedtls_ssl_config_defaults() unless you manually set all of the relevant fields yourself.

Parameters:: conf – SSL configuration context

int mbedtls_ssl_config_defaults(mbedtls_ssl_config *conf, int endpoint, int transport, int preset)

Load reasonable default SSL configuration values. (You need to call mbedtls_ssl_config_init() first.)

Note

See mbedtls_ssl_conf_transport() for notes on DTLS.

Parameters:

conf – SSL configuration context
endpoint – MBEDTLS_SSL_IS_CLIENT or MBEDTLS_SSL_IS_SERVER
transport – MBEDTLS_SSL_TRANSPORT_STREAM for TLS, or MBEDTLS_SSL_TRANSPORT_DATAGRAM for DTLS
preset – a MBEDTLS_SSL_PRESET_XXX value

Returns:

0 if successful, or MBEDTLS_ERR_XXX_ALLOC_FAILED on memory allocation error.

void mbedtls_ssl_config_free(mbedtls_ssl_config *conf)

Free an SSL configuration context.

Parameters:: conf – SSL configuration context

void mbedtls_ssl_session_init(mbedtls_ssl_session *session)

Initialize SSL session structure.

Parameters:: session – SSL session

void mbedtls_ssl_session_free(mbedtls_ssl_session *session)

Free referenced items in an SSL session including the peer certificate and clear memory.

Note

A session object can be freed even if the SSL context that was used to retrieve the session is still in use.

Parameters:: session – SSL session

int mbedtls_ssl_tls_prf(const mbedtls_tls_prf_types prf, const unsigned char *secret, size_t slen, const char *label, const unsigned char *random, size_t rlen, unsigned char *dstbuf, size_t dlen)

TLS-PRF function for key derivation.

Parameters:

prf – The tls_prf type function type to be used.
secret – Secret for the key derivation function.
slen – Length of the secret.
label – String label for the key derivation function, terminated with null character.
random – Random bytes.
rlen – Length of the random bytes buffer.
dstbuf – The buffer holding the derived key.
dlen – Length of the output buffer.

Returns:

0 on success. An SSL specific error on failure.

union mbedtls_ssl_premaster_secret

#include <ssl.h>

Public Members

unsigned char dummy

unsigned char _pms_rsa[48]

unsigned char _pms_dhm[MBEDTLS_MPI_MAX_SIZE]

unsigned char _pms_ecdh[MBEDTLS_ECP_MAX_BYTES]

unsigned char _pms_psk[4 + 2 * MBEDTLS_PSK_MAX_LEN]

unsigned char _pms_dhe_psk[4 + MBEDTLS_MPI_MAX_SIZE + MBEDTLS_PSK_MAX_LEN]

unsigned char _pms_rsa_psk[52 + MBEDTLS_PSK_MAX_LEN]

unsigned char _pms_ecdhe_psk[4 + MBEDTLS_ECP_MAX_BYTES + MBEDTLS_PSK_MAX_LEN]

unsigned char _pms_ecjpake[32]

struct mbedtls_dtls_srtp_info_t

#include <ssl.h>

Public Members

mbedtls_ssl_srtp_profile chosen_dtls_srtp_profile: The SRTP profile that was negotiated.

uint16_t mki_len: The length of mki_value.

unsigned char mki_value[MBEDTLS_TLS_SRTP_MAX_MKI_LENGTH]: The mki_value used, with max size of 256 bytes.

struct mbedtls_ssl_session

#include <ssl.h>

Public Members

unsigned char mfl_code: MaxFragmentLength negotiated by peer

mbedtls_time_t start: starting time

int ciphersuite: chosen ciphersuite

int compression: chosen compression

size_t id_len: session id length

unsigned char id[32]: session identifier

unsigned char master[48]: the master secret

mbedtls_x509_crt *peer_cert: peer X.509 cert chain

uint32_t verify_result: verification result

unsigned char *ticket: RFC 5077 session ticket

size_t ticket_len: session ticket length

uint32_t ticket_lifetime: ticket lifetime hint

int trunc_hmac: flag for truncated hmac activation

int encrypt_then_mac: flag for EtM activation

struct mbedtls_ssl_config

#include <ssl.h>

SSL/TLS configuration to be shared between mbedtls_ssl_context structures.

Public Members

unsigned char max_major_ver: max. major version used

unsigned char max_minor_ver: max. minor version used

unsigned char min_major_ver: min. major version used

unsigned char min_minor_ver: min. minor version used

uint8_t endpoint: 0: client, 1: server

uint8_t transport: stream (TLS) or datagram (DTLS)

uint8_t authmode: MBEDTLS_SSL_VERIFY_XXX

uint8_t allow_legacy_renegotiation: MBEDTLS_LEGACY_XXX

uint8_t arc4_disabled: blacklist RC4 ciphersuites?

uint8_t mfl_code: desired fragment length

uint8_t encrypt_then_mac: negotiate encrypt-then-mac?

uint8_t extended_ms: negotiate extended master secret?

uint8_t anti_replay: detect and prevent replay?

uint8_t cbc_record_splitting: do cbc record splitting

uint8_t disable_renegotiation: disable renegotiation?

uint8_t trunc_hmac: negotiate truncated hmac?

uint8_t session_tickets: use session tickets?

uint8_t fallback: is this a fallback?

uint8_t cert_req_ca_list: enable sending CA list in Certificate Request messages?

uint8_t ignore_unexpected_cid: Determines whether DTLS record with unexpected CID should lead to failure.

uint8_t dtls_srtp_mki_support: support having mki_value in the use_srtp extension?

uint32_t read_timeout: timeout for mbedtls_ssl_read (ms)

uint32_t hs_timeout_min: initial value of the handshake retransmission timeout (ms)

uint32_t hs_timeout_max: maximum value of the handshake retransmission timeout (ms)

int renego_max_records: grace period for renegotiation

unsigned char renego_period[8]: value of the record counters that triggers renegotiation

unsigned int badmac_limit: limit of records with a bad MAC

unsigned int dhm_min_bitlen: min. bit length of the DHM prime

const int *ciphersuite_list[4]: allowed ciphersuites per version

void (*f_dbg)(void*, int, const char*, int, const char*): Callback for printing debug output

void *p_dbg: context for the debug function

int (*f_rng)(void*, unsigned char*, size_t): Callback for getting (pseudo-)random numbers

void *p_rng: context for the RNG function

int (*f_get_cache)(void*, mbedtls_ssl_session*): Callback to retrieve a session from the cache

int (*f_set_cache)(void*, const mbedtls_ssl_session*): Callback to store a session into the cache

void *p_cache: context for cache callbacks

int (*f_sni)(void*, mbedtls_ssl_context*, const unsigned char*, size_t): Callback for setting cert according to SNI extension

void *p_sni: context for SNI callback

int (*f_vrfy)(void*, mbedtls_x509_crt*, int, uint32_t*): Callback to customize X.509 certificate chain verification

void *p_vrfy: context for X.509 verify calllback

int (*f_psk)(void*, mbedtls_ssl_context*, const unsigned char*, size_t): Callback to retrieve PSK key from identity

void *p_psk: context for PSK callback

int (*f_cookie_write)(void*, unsigned char**, unsigned char*, const unsigned char*, size_t): Callback to create & write a cookie for ClientHello verification

int (*f_cookie_check)(void*, const unsigned char*, size_t, const unsigned char*, size_t): Callback to verify validity of a ClientHello cookie

void *p_cookie: context for the cookie callbacks

int (*f_ticket_write)(void*, const mbedtls_ssl_session*, unsigned char*, const unsigned char*, size_t*, uint32_t*): Callback to create & write a session ticket

int (*f_ticket_parse)(void*, mbedtls_ssl_session*, unsigned char*, size_t): Callback to parse a session ticket into a session structure

void *p_ticket: context for the ticket callbacks

int (*f_export_keys)(void*, const unsigned char*, const unsigned char*, size_t, size_t, size_t): Callback to export key block and master secret

int (*f_export_keys_ext)(void*, const unsigned char*, const unsigned char*, size_t, size_t, size_t, const unsigned char[32], const unsigned char[32], mbedtls_tls_prf_types): Callback to export key block, master secret, tls_prf and random bytes. Should replace f_export_keys

void *p_export_keys: context for key export callback

size_t cid_len: The length of CIDs for incoming DTLS records.

const mbedtls_x509_crt_profile *cert_profile: verification profile

mbedtls_ssl_key_cert *key_cert: own certificate/key pair(s)

mbedtls_x509_crt *ca_chain: trusted CAs

mbedtls_x509_crl *ca_crl: trusted CAs CRLs

mbedtls_x509_crt_ca_cb_t f_ca_cb

void *p_ca_cb

mbedtls_ssl_async_sign_t *f_async_sign_start: start asynchronous signature operation

mbedtls_ssl_async_decrypt_t *f_async_decrypt_start: start asynchronous decryption operation

mbedtls_ssl_async_resume_t *f_async_resume: resume asynchronous operation

mbedtls_ssl_async_cancel_t *f_async_cancel: cancel asynchronous operation

void *p_async_config_data: Configuration data set by mbedtls_ssl_conf_async_private_cb().

const int *sig_hashes: allowed signature hashes

const mbedtls_ecp_group_id *curve_list: allowed curves

mbedtls_mpi dhm_P: prime modulus for DHM

mbedtls_mpi dhm_G: generator for DHM

psa_key_id_t psk_opaque: PSA key slot holding opaque PSK. This field should only be set via mbedtls_ssl_conf_psk_opaque(). If either no PSK or a raw PSK have been configured, this has value 0.

unsigned char *psk: The raw pre-shared key. This field should only be set via mbedtls_ssl_conf_psk(). If either no PSK or an opaque PSK have been configured, this has value NULL.

size_t psk_len: The length of the raw pre-shared key. This field should only be set via mbedtls_ssl_conf_psk(). Its value is non-zero if and only if psk is not NULL.

unsigned char *psk_identity: The PSK identity for PSK negotiation. This field should only be set via mbedtls_ssl_conf_psk(). This is set if and only if either psk or psk_opaque are set.

size_t psk_identity_len: The length of PSK identity. This field should only be set via mbedtls_ssl_conf_psk(). Its value is non-zero if and only if psk is not NULL or psk_opaque is not 0.

const char **alpn_list: ordered list of protocols

const mbedtls_ssl_srtp_profile *dtls_srtp_profile_list: ordered list of supported srtp profile

size_t dtls_srtp_profile_list_len: number of supported profiles

struct mbedtls_ssl_context

#include <ssl.h>

Public Members

const mbedtls_ssl_config *conf: configuration information

int state: SSL handshake: current state

int renego_status: Initial, in progress, pending?

int renego_records_seen: Records since renego request, or with DTLS, number of retransmissions of request if renego_max_records is < 0

int major_ver: equal to MBEDTLS_SSL_MAJOR_VERSION_3

int minor_ver: either 0 (SSL3) or 1 (TLS1.0)

unsigned badmac_seen: records with a bad MAC received

int (*f_vrfy)(void*, mbedtls_x509_crt*, int, uint32_t*): Callback to customize X.509 certificate chain verification

void *p_vrfy: context for X.509 verify callback

mbedtls_ssl_send_t *f_send: Callback for network send

mbedtls_ssl_recv_t *f_recv: Callback for network receive

mbedtls_ssl_recv_timeout_t *f_recv_timeout: Callback for network receive with timeout

void *p_bio: context for I/O operations

mbedtls_ssl_session *session_in: current session data (in)

mbedtls_ssl_session *session_out: current session data (out)

mbedtls_ssl_session *session: negotiated session data

mbedtls_ssl_session *session_negotiate: session data in negotiation

mbedtls_ssl_handshake_params *handshake: params required only during the handshake process

mbedtls_ssl_transform *transform_in: current transform params (in)

mbedtls_ssl_transform *transform_out: current transform params (in)

mbedtls_ssl_transform *transform: negotiated transform params

mbedtls_ssl_transform *transform_negotiate: transform params in negotiation

void *p_timer: context for the timer callbacks

mbedtls_ssl_set_timer_t *f_set_timer: set timer callback

mbedtls_ssl_get_timer_t *f_get_timer: get timer callback

unsigned char *in_buf: input buffer

unsigned char *in_ctr: 64-bit incoming message counter TLS: maintained by us DTLS: read from peer

unsigned char *in_hdr: start of record header

unsigned char *in_cid: The start of the CID; (the end is marked by in_len).

unsigned char *in_len: two-bytes message length field

unsigned char *in_iv: ivlen-byte IV

unsigned char *in_msg: message contents (in_iv+ivlen)

unsigned char *in_offt: read offset in application data

int in_msgtype: record header: message type

size_t in_msglen: record header: message length

size_t in_left: amount of data read so far

size_t in_buf_len: length of input buffer

uint16_t in_epoch: DTLS epoch for incoming records

size_t next_record_offset: offset of the next record in datagram (equal to in_left if none)

uint64_t in_window_top: last validated record seq_num

uint64_t in_window: bitmask for replay detection

size_t in_hslen: current handshake message length, including the handshake header

int nb_zero: of 0-length encrypted messages

int keep_current_message: drop or reuse current message on next call to record layer?

uint8_t disable_datagram_packing: Disable packing multiple records within a single datagram.

unsigned char *out_buf: output buffer

unsigned char *out_ctr: 64-bit outgoing message counter

unsigned char *out_hdr: start of record header

unsigned char *out_cid: The start of the CID; (the end is marked by in_len).

unsigned char *out_len: two-bytes message length field

unsigned char *out_iv: ivlen-byte IV

unsigned char *out_msg: message contents (out_iv+ivlen)

int out_msgtype: record header: message type

size_t out_msglen: record header: message length

size_t out_left: amount of data not yet written

size_t out_buf_len: length of output buffer

unsigned char cur_out_ctr[8]: Outgoing record sequence number.

uint16_t mtu: path mtu, used to fragment outgoing messages

unsigned char *compress_buf: zlib data buffer

signed char split_done: current record already split?

int client_auth: flag for client auth.

char *hostname

Expected peer CN for verification.

Also used on clients for SNI.

The value of this field can be:

NULL in a newly initialized or reset context.
A heap-allocated copy of the last value passed to mbedtls_ssl_set_hostname(), if the last call had a non-null hostname argument.
A special value to indicate that mbedtls_ssl_set_hostname() was called with NULL (as opposed to never having been called).

If you need to obtain the value passed to mbedtls_ssl_set_hostname() even if it may have been called with NULL, call mbedtls_ssl_get_hostname_pointer().

If this field contains the value NULL and the configuration option MBEDTLS_SSL_CLI_ALLOW_WEAK_CERTIFICATE_VERIFICATION_WITHOUT_HOSTNAME is unset, on a TLS client, attempting to verify a server certificate results in the error MBEDTLS_ERR_SSL_CERTIFICATE_VERIFICATION_WITHOUT_HOSTNAME.

If this field contains the special value described above, or if the value is NULL and the configuration option MBEDTLS_SSL_CLI_ALLOW_WEAK_CERTIFICATE_VERIFICATION_WITHOUT_HOSTNAME is set, then the peer name verification is skipped, which may be insecure, especially on a client. Furthermore, on a client, the server_name extension is not sent.

const char *alpn_chosen: negotiated protocol

mbedtls_dtls_srtp_info dtls_srtp_info

unsigned char *cli_id: transport-level ID of the client

size_t cli_id_len: length of cli_id

int secure_renegotiation: does peer support legacy or secure renegotiation

size_t verify_data_len: length of verify data stored

char own_verify_data[MBEDTLS_SSL_VERIFY_DATA_MAX_LEN]: previous handshake verify data

char peer_verify_data[MBEDTLS_SSL_VERIFY_DATA_MAX_LEN]: previous handshake verify data

unsigned char own_cid[MBEDTLS_SSL_CID_IN_LEN_MAX]: The next incoming CID, chosen by the user and applying to all subsequent handshakes. This may be different from the CID currently used in case the user has re-configured the CID after an initial handshake.

uint8_t own_cid_len: The length of own_cid.

uint8_t negotiate_cid: This indicates whether the CID extension should be negotiated in the next handshake or not. Possible values are MBEDTLS_SSL_CID_ENABLED and MBEDTLS_SSL_CID_DISABLED.

File ssl.h

of 0-length encrypted messages