File ccm.h

This file provides an API for the CCM authenticated encryption mode for block ciphers.

CCM combines Counter mode encryption with CBC-MAC authentication for 128-bit block ciphers.

Input to CCM includes the following elements:

  • Payload - data that is both authenticated and encrypted.

  • Associated data (Adata) - data that is authenticated but not encrypted, For example, a header.

  • Nonce - A unique value that is assigned to the payload and the associated data.

Definition of CCM: http://csrc.nist.gov/publications/nistpubs/800-38C/SP800-38C_updated-July20_2007.pdf RFC 3610 “Counter with CBC-MAC (CCM)”

Related: RFC 5116 “An Interface and Algorithms for Authenticated Encryption”

Definition of CCM*: IEEE 802.15.4 - IEEE Standard for Local and metropolitan area networks Integer representation is fixed most-significant-octet-first order and the representation of octets is most-significant-bit-first order. This is consistent with RFC 3610.

Defines

MBEDTLS_CCM_DECRYPT
MBEDTLS_CCM_ENCRYPT
MBEDTLS_CCM_STAR_DECRYPT
MBEDTLS_CCM_STAR_ENCRYPT
MBEDTLS_ERR_CCM_BAD_INPUT

Bad input parameters to the function.

MBEDTLS_ERR_CCM_AUTH_FAILED

Authenticated decryption failed.

Functions

void mbedtls_ccm_init(mbedtls_ccm_context *ctx)

This function initializes the specified CCM context, to make references valid, and prepare the context for mbedtls_ccm_setkey() or mbedtls_ccm_free().

Parameters

ctx – The CCM context to initialize. This must not be NULL.

int mbedtls_ccm_setkey(mbedtls_ccm_context *ctx, mbedtls_cipher_id_t cipher, const unsigned char *key, unsigned int keybits)

This function initializes the CCM context set in the ctx parameter and sets the encryption key.

Parameters

  • ctx – The CCM context to initialize. This must be an initialized context.

  • cipher – The 128-bit block cipher to use.

  • key – The encryption key. This must not be NULL.

  • keybits – The key size in bits. This must be acceptable by the cipher.

Returns

0 on success.

Returns

A CCM or cipher-specific error code on failure.

void mbedtls_ccm_free(mbedtls_ccm_context *ctx)

This function releases and clears the specified CCM context and underlying cipher sub-context.

Parameters

ctx – The CCM context to clear. If this is NULL, the function has no effect. Otherwise, this must be initialized.

int mbedtls_ccm_encrypt_and_tag(mbedtls_ccm_context *ctx, size_t length, const unsigned char *iv, size_t iv_len, const unsigned char *ad, size_t ad_len, const unsigned char *input, unsigned char *output, unsigned char *tag, size_t tag_len)

This function encrypts a buffer using CCM.

Note

The tag is written to a separate buffer. To concatenate the tag with the output, as done in RFC-3610: Counter with CBC-MAC (CCM), use tag = output + length, and make sure that the output buffer is at least length + tag_len wide.

Parameters

  • ctx – The CCM context to use for encryption. This must be initialized and bound to a key.

  • length – The length of the input data in Bytes.

  • iv – The initialization vector (nonce). This must be a readable buffer of at least iv_len Bytes.

  • iv_len – The length of the nonce in Bytes: 7, 8, 9, 10, 11, 12, or 13. The length L of the message length field is 15 - iv_len.

  • ad – The additional data field. If ad_len is greater than zero, ad must be a readable buffer of at least that length.

  • ad_len – The length of additional data in Bytes. This must be less than 2^16 - 2^8.

  • input – The buffer holding the input data. If length is greater than zero, input must be a readable buffer of at least that length.

  • output – The buffer holding the output data. If length is greater than zero, output must be a writable buffer of at least that length.

  • tag – The buffer holding the authentication field. This must be a writable buffer of at least tag_len Bytes.

  • tag_len – The length of the authentication field to generate in Bytes: 4, 6, 8, 10, 12, 14 or 16.

Returns

0 on success.

Returns

A CCM or cipher-specific error code on failure.

int mbedtls_ccm_star_encrypt_and_tag(mbedtls_ccm_context *ctx, size_t length, const unsigned char *iv, size_t iv_len, const unsigned char *ad, size_t ad_len, const unsigned char *input, unsigned char *output, unsigned char *tag, size_t tag_len)

This function encrypts a buffer using CCM*.

Note

The tag is written to a separate buffer. To concatenate the tag with the output, as done in RFC-3610: Counter with CBC-MAC (CCM), use tag = output + length, and make sure that the output buffer is at least length + tag_len wide.

Note

When using this function in a variable tag length context, the tag length has to be encoded into the iv passed to this function.

Warning

Passing 0 as tag_len means that the message is no longer authenticated.

Parameters

  • ctx – The CCM context to use for encryption. This must be initialized and bound to a key.

  • length – The length of the input data in Bytes. For tag length = 0, input length is ignored.

  • iv – The initialization vector (nonce). This must be a readable buffer of at least iv_len Bytes.

  • iv_len – The length of the nonce in Bytes: 7, 8, 9, 10, 11, 12, or 13. The length L of the message length field is 15 - iv_len.

  • ad – The additional data field. This must be a readable buffer of at least ad_len Bytes.

  • ad_len – The length of additional data in Bytes. This must be less than 2^16 - 2^8.

  • input – The buffer holding the input data. If length is greater than zero, input must be a readable buffer of at least that length.

  • output – The buffer holding the output data. If length is greater than zero, output must be a writable buffer of at least that length.

  • tag – The buffer holding the authentication field. This must be a writable buffer of at least tag_len Bytes.

  • tag_len – The length of the authentication field to generate in Bytes: 0, 4, 6, 8, 10, 12, 14 or 16.

Returns

0 on success.

Returns

A CCM or cipher-specific error code on failure.

int mbedtls_ccm_auth_decrypt(mbedtls_ccm_context *ctx, size_t length, const unsigned char *iv, size_t iv_len, const unsigned char *ad, size_t ad_len, const unsigned char *input, unsigned char *output, const unsigned char *tag, size_t tag_len)

This function performs a CCM authenticated decryption of a buffer.

Parameters

  • ctx – The CCM context to use for decryption. This must be initialized and bound to a key.

  • length – The length of the input data in Bytes.

  • iv – The initialization vector (nonce). This must be a readable buffer of at least iv_len Bytes.

  • iv_len – The length of the nonce in Bytes: 7, 8, 9, 10, 11, 12, or 13. The length L of the message length field is 15 - iv_len.

  • ad – The additional data field. This must be a readable buffer of at least that ad_len Bytes..

  • ad_len – The length of additional data in Bytes. This must be less than 2^16 - 2^8.

  • input – The buffer holding the input data. If length is greater than zero, input must be a readable buffer of at least that length.

  • output – The buffer holding the output data. If length is greater than zero, output must be a writable buffer of at least that length.

  • tag – The buffer holding the authentication field. This must be a readable buffer of at least tag_len Bytes.

  • tag_len – The length of the authentication field to generate in Bytes: 4, 6, 8, 10, 12, 14 or 16.

Returns

0 on success. This indicates that the message is authentic.

Returns

MBEDTLS_ERR_CCM_AUTH_FAILED if the tag does not match.

Returns

A cipher-specific error code on calculation failure.

int mbedtls_ccm_star_auth_decrypt(mbedtls_ccm_context *ctx, size_t length, const unsigned char *iv, size_t iv_len, const unsigned char *ad, size_t ad_len, const unsigned char *input, unsigned char *output, const unsigned char *tag, size_t tag_len)

This function performs a CCM* authenticated decryption of a buffer.

Note

When using this function in a variable tag length context, the tag length has to be decoded from iv and passed to this function as tag_len. (tag needs to be adjusted accordingly.)

Warning

Passing 0 as tag_len means that the message is nos longer authenticated.

Parameters

  • ctx – The CCM context to use for decryption. This must be initialized and bound to a key.

  • length – The length of the input data in Bytes. For tag length = 0, input length is ignored.

  • iv – The initialization vector (nonce). This must be a readable buffer of at least iv_len Bytes.

  • iv_len – The length of the nonce in Bytes: 7, 8, 9, 10, 11, 12, or 13. The length L of the message length field is 15 - iv_len.

  • ad – The additional data field. This must be a readable buffer of at least that ad_len Bytes.

  • ad_len – The length of additional data in Bytes. This must be less than 2^16 - 2^8.

  • input – The buffer holding the input data. If length is greater than zero, input must be a readable buffer of at least that length.

  • output – The buffer holding the output data. If length is greater than zero, output must be a writable buffer of at least that length.

  • tag – The buffer holding the authentication field. This must be a readable buffer of at least tag_len Bytes.

  • tag_len – The length of the authentication field in Bytes. 0, 4, 6, 8, 10, 12, 14 or 16.

Returns

0 on success.

Returns

MBEDTLS_ERR_CCM_AUTH_FAILED if the tag does not match.

Returns

A cipher-specific error code on calculation failure.

int mbedtls_ccm_starts(mbedtls_ccm_context *ctx, int mode, const unsigned char *iv, size_t iv_len)

This function starts a CCM encryption or decryption operation.

This function and mbedtls_ccm_set_lengths() must be called before calling mbedtls_ccm_update_ad() or mbedtls_ccm_update(). This function can be called before or after mbedtls_ccm_set_lengths().

Note

This function is not implemented in Mbed TLS yet.

Parameters
Returns

0 on success.

Returns

MBEDTLS_ERR_CCM_BAD_INPUT on failure: ctx is in an invalid state, mode is invalid, iv_len is invalid (lower than 7 or greater than 13).

int mbedtls_ccm_set_lengths(mbedtls_ccm_context *ctx, size_t total_ad_len, size_t plaintext_len, size_t tag_len)

This function declares the lengths of the message and additional data for a CCM encryption or decryption operation.

This function and mbedtls_ccm_starts() must be called before calling mbedtls_ccm_update_ad() or mbedtls_ccm_update(). This function can be called before or after mbedtls_ccm_starts().

Note

This function is not implemented in Mbed TLS yet.

Parameters

  • ctx – The CCM context. This must be initialized.

  • total_ad_len – The total length of additional data in bytes. This must be less than 2^16 - 2^8.

  • plaintext_len – The length in bytes of the plaintext to encrypt or result of the decryption (thus not encompassing the additional data that are not encrypted).

  • tag_len – The length of the tag to generate in Bytes: 4, 6, 8, 10, 12, 14 or 16. For CCM*, zero is also valid.

Returns

0 on success.

Returns

MBEDTLS_ERR_CCM_BAD_INPUT on failure: ctx is in an invalid state, total_ad_len is greater than 0xFF00.

int mbedtls_ccm_update_ad(mbedtls_ccm_context *ctx, const unsigned char *ad, size_t ad_len)

This function feeds an input buffer as associated data (authenticated but not encrypted data) in a CCM encryption or decryption operation.

You may call this function zero, one or more times to pass successive parts of the additional data. The lengths ad_len of the data parts should eventually add up exactly to the total length of additional data total_ad_len passed to mbedtls_ccm_set_lengths(). You may not call this function after calling mbedtls_ccm_update().

Note

This function is not implemented in Mbed TLS yet.

Parameters

  • ctx – The CCM context. This must have been started with mbedtls_ccm_starts(), the lengths of the message and additional data must have been declared with mbedtls_ccm_set_lengths() and this must not have yet received any input with mbedtls_ccm_update().

  • ad – The buffer holding the additional data, or NULL if ad_len is 0.

  • ad_len – The length of the additional data. If 0, ad may be NULL.

Returns

0 on success.

Returns

MBEDTLS_ERR_CCM_BAD_INPUT on failure: ctx is in an invalid state, total input length too long.

int mbedtls_ccm_update(mbedtls_ccm_context *ctx, const unsigned char *input, size_t input_len, unsigned char *output, size_t output_size, size_t *output_len)

This function feeds an input buffer into an ongoing CCM encryption or decryption operation.

You may call this function zero, one or more times to pass successive parts of the input: the plaintext to encrypt, or the ciphertext (not including the tag) to decrypt. After the last part of the input, call mbedtls_ccm_finish(). The lengths input_len of the data parts should eventually add up exactly to the plaintext length plaintext_len passed to mbedtls_ccm_set_lengths().

This function may produce output in one of the following ways:

  • Immediate output: the output length is always equal to the input length.

  • Buffered output: except for the last part of input data, the output consists of a whole number of 16-byte blocks. If the total input length so far (not including associated data) is 16 * B + A with A < 16 then the total output length is 16 * B. For the last part of input data, the output length is equal to the input length plus the number of bytes (A) buffered in the previous call to the function (if any). The function uses the plaintext length plaintext_len passed to mbedtls_ccm_set_lengths() to detect the last part of input data.

In particular:

  • It is always correct to call this function with output_size >= input_len + 15.

  • If input_len is a multiple of 16 for all the calls to this function during an operation (not necessary for the last one) then it is correct to use output_size =input_len.

Note

This function is not implemented in Mbed TLS yet.

Parameters

  • ctx – The CCM context. This must have been started with mbedtls_ccm_starts() and the lengths of the message and additional data must have been declared with mbedtls_ccm_set_lengths().

  • input – The buffer holding the input data. If input_len is greater than zero, this must be a readable buffer of at least input_len bytes.

  • input_len – The length of the input data in bytes.

  • output – The buffer for the output data. If output_size is greater than zero, this must be a writable buffer of at least output_size bytes.

  • output_size – The size of the output buffer in bytes. See the function description regarding the output size.

  • output_len – On success, *output_len contains the actual length of the output written in output. On failure, the content of *output_len is unspecified.

Returns

0 on success.

Returns

MBEDTLS_ERR_CCM_BAD_INPUT on failure: ctx is in an invalid state, total input length too long, or output_size too small.

int mbedtls_ccm_finish(mbedtls_ccm_context *ctx, unsigned char *tag, size_t tag_len)

This function finishes the CCM operation and generates the authentication tag.

It wraps up the CCM stream, and generates the tag. The tag can have a maximum length of 16 Bytes.

Note

This function is not implemented in Mbed TLS yet.

Parameters

  • ctx – The CCM context. This must have been started with mbedtls_ccm_starts() and the lengths of the message and additional data must have been declared with mbedtls_ccm_set_lengths().

  • tag – The buffer for holding the tag. If tag_len is greater than zero, this must be a writable buffer of at least tag_len Bytes.

  • tag_len – The length of the tag. Must match the tag length passed to mbedtls_ccm_set_lengths() function.

Returns

0 on success.

Returns

MBEDTLS_ERR_CCM_BAD_INPUT on failure: ctx is in an invalid state, invalid value of tag_len, the total amount of additional data passed to mbedtls_ccm_update_ad() was lower than the total length of additional data total_ad_len passed to mbedtls_ccm_set_lengths(), the total amount of input data passed to mbedtls_ccm_update() was lower than the plaintext length plaintext_len passed to mbedtls_ccm_set_lengths().

int mbedtls_ccm_self_test(int verbose)

The CCM checkup routine.

Returns

0 on success.

Returns

1 on failure.