hmac.h File Reference

Interface to an HMAC implementation. More...

Go to the source code of this file.

Functions
int	tc_hmac_set_key (TCHmacState_t ctx, const uint8_t *key, unsigned int key_size)
	HMAC set key procedure Configures ctx to use key.
int	tc_hmac_init (TCHmacState_t ctx)
	HMAC init procedure Initializes ctx to begin the next HMAC operation.
int	tc_hmac_update (TCHmacState_t ctx, const void *data, unsigned int data_length)
	HMAC update procedure Mixes data_length bytes addressed by data into state.
int	tc_hmac_final (uint8_t *tag, unsigned int taglen, TCHmacState_t ctx)
	HMAC final procedure Writes the HMAC tag into the tag buffer.

Detailed Description

Interface to an HMAC implementation.

Overview: HMAC is a message authentication code based on hash functions. TinyCrypt hard codes SHA-256 as the hash function. A message authentication code based on hash functions is also called a keyed cryptographic hash function since it performs a transformation specified by a key in an arbitrary length data set into a fixed length data set (also called tag).

Security: The security of the HMAC depends on the length of the key and on the security of the hash function. Note that HMAC primitives are much less affected by collision attacks than their corresponding hash functions.

Requires: SHA-256

Usage: 1) call tc_hmac_set_key to set the HMAC key.

        2) call tc_hmac_init to initialize a struct hash_state before
        processing the data.

        3) call tc_hmac_update to process the next input segment;
        tc_hmac_update can be called as many times as needed to process
        all of the segments of the input; the order is important.

        4) call tc_hmac_final to out put the tag.

Function Documentation

tc_hmac_final()

int tc_hmac_final	(	uint8_t *	tag,
		unsigned int	taglen,
		TCHmacState_t	ctx
	)

HMAC final procedure Writes the HMAC tag into the tag buffer.

Returns

returns TC_CRYPTO_SUCCESS (1) returns TC_CRYPTO_FAIL (0) if: tag == NULL or ctx == NULL or key == NULL or taglen != TC_SHA256_DIGEST_SIZE

Note

ctx is erased before exiting. This should never be changed/removed.

Assumes the tag bufer is at least sizeof(hmac_tag_size(state)) bytes state has been initialized by tc_hmac_init

Parameters

tag	IN/OUT – buffer to receive computed HMAC tag
taglen	IN – size of tag in bytes
ctx	IN/OUT – the HMAC state for computing tag

tc_hmac_init()

int tc_hmac_init

(

TCHmacState_t

ctx

)

HMAC init procedure Initializes ctx to begin the next HMAC operation.

Returns

returns TC_CRYPTO_SUCCESS (1) returns TC_CRYPTO_FAIL (0) if: ctx == NULL or key == NULL

Parameters

ctx	IN/OUT – struct tc_hmac_state_struct buffer to init

tc_hmac_set_key()

int tc_hmac_set_key	(	TCHmacState_t	ctx,
		const uint8_t *	key,
		unsigned int	key_size
	)

HMAC set key procedure Configures ctx to use key.

Returns

returns TC_CRYPTO_SUCCESS (1) returns TC_CRYPTO_FAIL (0) if ctx == NULL or key == NULL or key_size == 0

Parameters

ctx	IN/OUT – the struct tc_hmac_state_struct to initial
key	IN – the HMAC key to configure
key_size	IN – the HMAC key size

tc_hmac_update()

int tc_hmac_update	(	TCHmacState_t	ctx,
		const void *	data,
		unsigned int	data_length
	)

HMAC update procedure Mixes data_length bytes addressed by data into state.

Returns

returns TC_CRYPTO_SUCCCESS (1) returns TC_CRYPTO_FAIL (0) if: ctx == NULL or key == NULL

Note

Assumes state has been initialized by tc_hmac_init

Parameters

ctx	IN/OUT – state of HMAC computation so far
data	IN – data to incorporate into state
data_length	IN – size of data in bytes