File aes.h

This file contains AES definitions and functions. 

     The Advanced Encryption Standard (AES) specifies a FIPS-approved
     cryptographic algorithm that can be used to protect electronic
     data.

     The AES algorithm is a symmetric block cipher that can
     encrypt and decrypt information. For more information, see
     <em>FIPS Publication 197: Advanced Encryption Standard</em> and
     <em>ISO/IEC 18033-2:2006: Information technology -- Security
     techniques -- Encryption algorithms -- Part 2: Asymmetric
     ciphers</em>.

     The AES-XTS block mode is standardized by NIST SP 800-38E
     <https://nvlpubs.nist.gov/nistpubs/legacy/sp/nistspecialpublication800-38e.pdf>
     and described in detail by IEEE P1619
     <https://ieeexplore.ieee.org/servlet/opac?punumber=4375278>.

Defines

MBEDTLS_AES_ENCRYPT

AES encryption.

MBEDTLS_AES_DECRYPT

AES decryption.

MBEDTLS_ERR_AES_INVALID_KEY_LENGTH

Invalid key length.

MBEDTLS_ERR_AES_INVALID_INPUT_LENGTH

Invalid data input length.

MBEDTLS_ERR_AES_BAD_INPUT_DATA

Invalid input data.

Functions

void mbedtls_aes_init(mbedtls_aes_context *ctx)

This function initializes the specified AES context. 

            It must be the first API called before using
            the context.
Parameters

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

void mbedtls_aes_free(mbedtls_aes_context *ctx)

This function releases and clears the specified AES context.

Parameters

ctx – The AES context to clear. If this is NULL, this function does nothing. Otherwise, the context must have been at least initialized.

void mbedtls_aes_xts_init(mbedtls_aes_xts_context *ctx)

This function initializes the specified AES XTS context. 

            It must be the first API called before using
            the context.
Parameters

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

void mbedtls_aes_xts_free(mbedtls_aes_xts_context *ctx)

This function releases and clears the specified AES XTS context.

Parameters

ctx – The AES XTS context to clear. If this is NULL, this function does nothing. Otherwise, the context must have been at least initialized.

int mbedtls_aes_setkey_enc(mbedtls_aes_context *ctx, const unsigned char *key, unsigned int keybits)

This function sets the encryption key.

Parameters

  • ctx – The AES context to which the key should be bound. It must be initialized.

  • key – The encryption key. This must be a readable buffer of size keybits bits.

  • keybits – The size of data passed in bits. Valid options are:

    • 128 bits

    • 192 bits

    • 256 bits

Returns

0 on success.

Returns

MBEDTLS_ERR_AES_INVALID_KEY_LENGTH on failure.

int mbedtls_aes_xts_setkey_enc(mbedtls_aes_xts_context *ctx, const unsigned char *key, unsigned int keybits)

This function prepares an XTS context for encryption and sets the encryption key.

Parameters

  • ctx – The AES XTS context to which the key should be bound. It must be initialized.

  • key – The encryption key. This is comprised of the XTS key1 concatenated with the XTS key2. This must be a readable buffer of size keybits bits.

  • keybits – The size of key passed in bits. Valid options are:

    • 256 bits (each of key1 and key2 is a 128-bit key)

    • 512 bits (each of key1 and key2 is a 256-bit key)

Returns

0 on success.

Returns

MBEDTLS_ERR_AES_INVALID_KEY_LENGTH on failure.

int mbedtls_aes_xts_setkey_dec(mbedtls_aes_xts_context *ctx, const unsigned char *key, unsigned int keybits)

This function prepares an XTS context for decryption and sets the decryption key.

Parameters

  • ctx – The AES XTS context to which the key should be bound. It must be initialized.

  • key – The decryption key. This is comprised of the XTS key1 concatenated with the XTS key2. This must be a readable buffer of size keybits bits.

  • keybits – The size of key passed in bits. Valid options are:

    • 256 bits (each of key1 and key2 is a 128-bit key)

    • 512 bits (each of key1 and key2 is a 256-bit key)

Returns

0 on success.

Returns

MBEDTLS_ERR_AES_INVALID_KEY_LENGTH on failure.

int mbedtls_aes_crypt_ecb(mbedtls_aes_context *ctx, int mode, const unsigned char input[16], unsigned char output[16])

This function performs an AES single-block encryption or decryption operation.

It performs the operation defined in the mode parameter (encrypt or decrypt), on the input data buffer defined in the input parameter.

mbedtls_aes_init(), and either mbedtls_aes_setkey_enc() or mbedtls_aes_setkey_dec() must be called before the first call to this API with the same context.

Parameters

  • ctx – The AES context to use for encryption or decryption. It must be initialized and bound to a key.

  • mode – The AES operation: MBEDTLS_AES_ENCRYPT or MBEDTLS_AES_DECRYPT.

  • input – The buffer holding the input data. It must be readable and at least 16 Bytes long.

  • output – The buffer where the output data will be written. It must be writeable and at least 16 Bytes long.

Returns

0 on success.

int mbedtls_aes_crypt_cbc(mbedtls_aes_context *ctx, int mode, size_t length, unsigned char iv[16], const unsigned char *input, unsigned char *output)

This function performs an AES-CBC encryption or decryption operation on full blocks.

It performs the operation defined in the mode parameter (encrypt/decrypt), on the input data buffer defined in the input parameter.

It can be called as many times as needed, until all the input data is processed. mbedtls_aes_init(), and either mbedtls_aes_setkey_enc() or mbedtls_aes_setkey_dec() must be called before the first call to this API with the same context.

Note

This function operates on full blocks, that is, the input size must be a multiple of the AES block size of 16 Bytes.

Note

Upon exit, the content of the IV is updated so that you can call the same function again on the next block(s) of data and get the same result as if it was encrypted in one call. This allows a “streaming” usage. If you need to retain the contents of the IV, you should either save it manually or use the cipher module instead.

Parameters

  • ctx – The AES context to use for encryption or decryption. It must be initialized and bound to a key.

  • mode – The AES operation: MBEDTLS_AES_ENCRYPT or MBEDTLS_AES_DECRYPT.

  • length – The length of the input data in Bytes. This must be a multiple of the block size (16 Bytes).

  • iv – Initialization vector (updated after use). It must be a readable and writeable buffer of 16 Bytes.

  • input – The buffer holding the input data. It must be readable and of size length Bytes.

  • output – The buffer holding the output data. It must be writeable and of size length Bytes.

Returns

0 on success.

Returns

MBEDTLS_ERR_AES_INVALID_INPUT_LENGTH on failure.

int mbedtls_aes_crypt_xts(mbedtls_aes_xts_context *ctx, int mode, size_t length, const unsigned char data_unit[16], const unsigned char *input, unsigned char *output)

This function performs an AES-XTS encryption or decryption operation for an entire XTS data unit.

AES-XTS encrypts or decrypts blocks based on their location as defined by a data unit number. The data unit number must be provided by data_unit.

NIST SP 800-38E limits the maximum size of a data unit to 2^20 AES blocks. If the data unit is larger than this, this function returns MBEDTLS_ERR_AES_INVALID_INPUT_LENGTH.

Parameters

  • ctx – The AES XTS context to use for AES XTS operations. It must be initialized and bound to a key.

  • mode – The AES operation: MBEDTLS_AES_ENCRYPT or MBEDTLS_AES_DECRYPT.

  • length – The length of a data unit in Bytes. This can be any length between 16 bytes and 2^24 bytes inclusive (between 1 and 2^20 block cipher blocks).

  • data_unit – The address of the data unit encoded as an array of 16 bytes in little-endian format. For disk encryption, this is typically the index of the block device sector that contains the data.

  • input – The buffer holding the input data (which is an entire data unit). This function reads length Bytes from input.

  • output – The buffer holding the output data (which is an entire data unit). This function writes length Bytes to output.

Returns

0 on success.

Returns

MBEDTLS_ERR_AES_INVALID_INPUT_LENGTH if length is smaller than an AES block in size (16 Bytes) or if length is larger than 2^20 blocks (16 MiB).

int mbedtls_aes_crypt_cfb128(mbedtls_aes_context *ctx, int mode, size_t length, size_t *iv_off, unsigned char iv[16], const unsigned char *input, unsigned char *output)

This function performs an AES-CFB128 encryption or decryption operation.

It performs the operation defined in the mode parameter (encrypt or decrypt), on the input data buffer defined in the input parameter.

For CFB, you must set up the context with mbedtls_aes_setkey_enc(), regardless of whether you are performing an encryption or decryption operation, that is, regardless of the mode parameter. This is because CFB mode uses the same key schedule for encryption and decryption.

Note

Upon exit, the content of the IV is updated so that you can call the same function again on the next block(s) of data and get the same result as if it was encrypted in one call. This allows a “streaming” usage. If you need to retain the contents of the IV, you must either save it manually or use the cipher module instead.

Parameters

  • ctx – The AES context to use for encryption or decryption. It must be initialized and bound to a key.

  • mode – The AES operation: MBEDTLS_AES_ENCRYPT or MBEDTLS_AES_DECRYPT.

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

  • iv_off – The offset in IV (updated after use). It must point to a valid size_t.

  • iv – The initialization vector (updated after use). It must be a readable and writeable buffer of 16 Bytes.

  • input – The buffer holding the input data. It must be readable and of size length Bytes.

  • output – The buffer holding the output data. It must be writeable and of size length Bytes.

Returns

0 on success.

int mbedtls_aes_crypt_cfb8(mbedtls_aes_context *ctx, int mode, size_t length, unsigned char iv[16], const unsigned char *input, unsigned char *output)

This function performs an AES-CFB8 encryption or decryption operation.

It performs the operation defined in the mode parameter (encrypt/decrypt), on the input data buffer defined in the input parameter.

Due to the nature of CFB, you must use the same key schedule for both encryption and decryption operations. Therefore, you must use the context initialized with mbedtls_aes_setkey_enc() for both MBEDTLS_AES_ENCRYPT and MBEDTLS_AES_DECRYPT.

Note

Upon exit, the content of the IV is updated so that you can call the same function again on the next block(s) of data and get the same result as if it was encrypted in one call. This allows a “streaming” usage. If you need to retain the contents of the IV, you should either save it manually or use the cipher module instead.

Parameters

  • ctx – The AES context to use for encryption or decryption. It must be initialized and bound to a key.

  • mode – The AES operation: MBEDTLS_AES_ENCRYPT or MBEDTLS_AES_DECRYPT

  • length – The length of the input data.

  • iv – The initialization vector (updated after use). It must be a readable and writeable buffer of 16 Bytes.

  • input – The buffer holding the input data. It must be readable and of size length Bytes.

  • output – The buffer holding the output data. It must be writeable and of size length Bytes.

Returns

0 on success.

int mbedtls_aes_crypt_ofb(mbedtls_aes_context *ctx, size_t length, size_t *iv_off, unsigned char iv[16], const unsigned char *input, unsigned char *output)

This function performs an AES-OFB (Output Feedback Mode) encryption or decryption operation.

For OFB, you must set up the context with mbedtls_aes_setkey_enc(), regardless of whether you are performing an encryption or decryption operation. This is because OFB mode uses the same key schedule for encryption and decryption.

The OFB operation is identical for encryption or decryption, therefore no operation mode needs to be specified.

For non-streaming use, the iv should be initialised on each call to a unique value, and iv_off set to 0 on each call.

If you need to retain the contents of the initialisation vector, you must either save it manually or use the cipher module instead.

Note

Upon exit, the content of iv, the Initialisation Vector, is updated so that you can call the same function again on the next block(s) of data and get the same result as if it was encrypted in one call. This allows a “streaming” usage, by initialising iv_off to 0 before the first call, and preserving its value between calls.

Warning

For the OFB mode, the initialisation vector must be unique every encryption operation. Reuse of an initialisation vector will compromise security.

Parameters

  • ctx – The AES context to use for encryption or decryption. It must be initialized and bound to a key.

  • length – The length of the input data.

  • iv_off – The offset in IV (updated after use). It must point to a valid size_t.

  • iv – The initialization vector (updated after use). It must be a readable and writeable buffer of 16 Bytes.

  • input – The buffer holding the input data. It must be readable and of size length Bytes.

  • output – The buffer holding the output data. It must be writeable and of size length Bytes.

Returns

0 on success.

int mbedtls_aes_crypt_ctr(mbedtls_aes_context *ctx, size_t length, size_t *nc_off, unsigned char nonce_counter[16], unsigned char stream_block[16], const unsigned char *input, unsigned char *output)

This function performs an AES-CTR encryption or decryption operation.

Due to the nature of CTR, you must use the same key schedule for both encryption and decryption operations. Therefore, you must use the context initialized with mbedtls_aes_setkey_enc() for both MBEDTLS_AES_ENCRYPT and MBEDTLS_AES_DECRYPT.

There are two common strategies for managing nonces with CTR:

  1. You can handle everything as a single message processed over successive calls to this function. In that case, you want to set nonce_counter and nc_off to 0 for the first call, and then preserve the values of nonce_counter, nc_off and stream_block across calls to this function as they will be updated by this function.

With this strategy, you must not encrypt more than 2**128 blocks of data with the same key.

  1. You can encrypt separate messages by dividing the nonce_counter buffer in two areas: the first one used for a per-message nonce, handled by yourself, and the second one updated by this function internally.

For example, you might reserve the first 12 bytes for the per-message nonce, and the last 4 bytes for internal use. In that case, before calling this function on a new message you need to set the first 12 bytes of nonce_counter to your chosen nonce value, the last 4 to 0, and nc_off to 0 (which will cause stream_block to be ignored). That way, you can encrypt at most 2**96 messages of up to 2**32 blocks each with the same key.

The per-message nonce (or information sufficient to reconstruct it) needs to be communicated with the ciphertext and must be unique. The recommended way to ensure uniqueness is to use a message counter. An alternative is to generate random nonces, but this limits the number of messages that can be securely encrypted: for example, with 96-bit random nonces, you should not encrypt more than 2**32 messages with the same key.

Note that for both strategies, sizes are measured in blocks and that an AES block is 16 bytes.

Warning

You must never reuse a nonce value with the same key. Doing so would void the encryption for the two messages encrypted with the same nonce and key.

Warning

Upon return, stream_block contains sensitive data. Its content must not be written to insecure storage and should be securely discarded as soon as it’s no longer needed.

Parameters

  • ctx – The AES context to use for encryption or decryption. It must be initialized and bound to a key.

  • length – The length of the input data.

  • nc_off – The offset in the current stream_block, for resuming within the current cipher stream. The offset pointer should be 0 at the start of a stream. It must point to a valid size_t.

  • nonce_counter – The 128-bit nonce and counter. It must be a readable-writeable buffer of 16 Bytes.

  • stream_block – The saved stream block for resuming. This is overwritten by the function. It must be a readable-writeable buffer of 16 Bytes.

  • input – The buffer holding the input data. It must be readable and of size length Bytes.

  • output – The buffer holding the output data. It must be writeable and of size length Bytes.

Returns

0 on success.

int mbedtls_internal_aes_encrypt(mbedtls_aes_context *ctx, const unsigned char input[16], unsigned char output[16])

Internal AES block encryption function. This is only exposed to allow overriding it using MBEDTLS_AES_ENCRYPT_ALT.

Parameters

  • ctx – The AES context to use for encryption.

  • input – The plaintext block.

  • output – The output (ciphertext) block.

Returns

0 on success.

int mbedtls_aes_self_test(int verbose)

Checkup routine.

Returns

0 on success.

Returns

1 on failure.