HMAC-SHA-2

The keyed message authentication codes HMAC-SHA-256, HMAC-SHA-512 and HMAC-SHA512-256 (truncated HMAC-SHA-512) are provided.
The crypto_auth API provides a simplified interface for message authentication.
If required, a streaming API is available to process a message as a sequence of multiple chunks.
Single-part example
#define MESSAGE ((const unsigned char *) "Arbitrary data to hash")
#define MESSAGE_LEN 22
​
unsigned char hash[crypto_auth_hmacsha512_BYTES];
unsigned char key[crypto_auth_hmacsha512_KEYBYTES];
​
crypto_auth_hmacsha512_keygen(key);
crypto_auth_hmacsha512(hash, MESSAGE, MESSAGE_LEN, key);
Multi-part example
#define MESSAGE_PART1 \
    ((const unsigned char *) "Arbitrary data to hash")
#define MESSAGE_PART1_LEN 22
​
#define MESSAGE_PART2 \
    ((const unsigned char *) "is longer than expected")
#define MESSAGE_PART2_LEN 23
​
unsigned char hash[crypto_auth_hmacsha512_BYTES];
unsigned char key[crypto_auth_hmacsha512_KEYBYTES];
crypto_auth_hmacsha512_state state;
​
crypto_auth_hmacsha512_keygen(key);
​
crypto_auth_hmacsha512_init(&state, key, sizeof key);
​
crypto_auth_hmacsha512_update(&state, MESSAGE_PART1, MESSAGE_PART1_LEN);
crypto_auth_hmacsha512_update(&state, MESSAGE_PART2, MESSAGE_PART2_LEN);
​
crypto_auth_hmacsha512_final(&state, hash);
Usage
HMAC-SHA-256
int crypto_auth_hmacsha256(unsigned char *out,
                           const unsigned char *in,
                           unsigned long long inlen,
                           const unsigned char *k);
The crypto_auth_hmacsha256() function authenticates a message in whose length is inlen using the secret key k whose length is crypto_auth_hmacsha256_KEYBYTES, and puts the authenticator into out (crypto_auth_hmacsha256_BYTES bytes).
int crypto_auth_hmacsha256_verify(const unsigned char *h,
                                  const unsigned char *in,
                                  unsigned long long inlen,
                                  const unsigned char *k);
The crypto_auth_hmacsha256_verify() function verifies in constant time that h is a correct authenticator for the message in whose length is inlen under a secret key k (crypto_auth_hmacsha256_KEYBYTES bytes).
It returns -1 if the verification fails, and 0 on success.
A multi-part (streaming) API can be used instead of crypto_auth_hmacsha256():
int crypto_auth_hmacsha256_init(crypto_auth_hmacsha256_state *state,
                                const unsigned char *key,
                                size_t keylen);
int crypto_auth_hmacsha256_update(crypto_auth_hmacsha256_state *state,
                                  const unsigned char *in,
                                  unsigned long long inlen);
int crypto_auth_hmacsha256_final(crypto_auth_hmacsha256_state *state,
                                 unsigned char *out);
This alternative API supports a key of arbitrary length keylen.
However, please note that in the HMAC construction, a key larger than the block size gets reduced to h(key).
void crypto_auth_hmacsha256_keygen(unsigned char k[crypto_auth_hmacsha256_KEYBYTES]);
This helper function introduced in libsodium 1.0.12 creates a random key k.
It is equivalent to calling randombytes_buf() but improves code clarity and can prevent misuse by ensuring that the provided key length is always be correct.
HMAC-SHA-512
Similarily to the crypto_auth_hmacsha256_*() set of functions, the crypto_auth_hmacsha512_*() set of functions implements HMAC-SHA512:
int crypto_auth_hmacsha512(unsigned char *out,
                           const unsigned char *in,
                           unsigned long long inlen,
                           const unsigned char *k);
int crypto_auth_hmacsha512_verify(const unsigned char *h,
                                  const unsigned char *in,
                                  unsigned long long inlen,
                                  const unsigned char *k);
int crypto_auth_hmacsha512_init(crypto_auth_hmacsha512_state *state,
                                const unsigned char *key,
                                size_t keylen);
int crypto_auth_hmacsha512_update(crypto_auth_hmacsha512_state *state,
                                  const unsigned char *in,
                                  unsigned long long inlen);
int crypto_auth_hmacsha512_final(crypto_auth_hmacsha512_state *state,
                                 unsigned char *out);
void crypto_auth_hmacsha512_keygen(unsigned char k[crypto_auth_hmacsha512_KEYBYTES]);
HMAC-SHA-512-256
HMAC-SHA-512-256 is implemented as HMAC-SHA-512 with the output truncated to 256 bits. This is slightly faster than HMAC-SHA-256. Note that this construction is not the same as HMAC-SHA-512/256, which is HMAC using the SHA-512/256 function.
int crypto_auth_hmacsha512256(unsigned char *out,
                              const unsigned char *in,
                              unsigned long long inlen,
                              const unsigned char *k);
int crypto_auth_hmacsha512256_verify(const unsigned char *h,
                                     const unsigned char *in,
                                     unsigned long long inlen,
                                     const unsigned char *k);
int crypto_auth_hmacsha512256_init(crypto_auth_hmacsha512256_state *state,
                                   const unsigned char *key,
                                   size_t keylen);
int crypto_auth_hmacsha512256_update(crypto_auth_hmacsha512256_state *state,
                                     const unsigned char *in,
                                     unsigned long long inlen);
int crypto_auth_hmacsha512256_final(crypto_auth_hmacsha512256_state *state,
                                    unsigned char *out);
void crypto_auth_hmacsha512256_keygen(unsigned char k[crypto_auth_hmacsha512256_KEYBYTES]);
Constants
crypto_auth_hmacsha256_BYTES
crypto_auth_hmacsha256_KEYBYTES
crypto_auth_hmacsha512_BYTES
crypto_auth_hmacsha512_KEYBYTES
crypto_auth_hmacsha512256_BYTES
crypto_auth_hmacsha512256_KEYBYTES
Data types
crypto_auth_hmacsha256_state
crypto_auth_hmacsha512_state
crypto_auth_hmacsha512256_state
Notes
The state must be initialized with crypto_auth_hmacsha*_init() before updating or finalizing it. After crypto_auth_hmacsha*_final() returns, the state should not be used any more, unless it is reinitialized using crypto_auth_hmacsha*_init().
Arbitrary key lengths are supported using the multi-part interface.
crypto_auth_hmacsha256_*() can be used to create AWS HMAC-SHA256 request signatures.
Only use these functions for interoperability with 3rd party services. For everything else, you should probably use crypto_auth()/crypto_auth_verify() or crypto_generichash_*() instead.
SHA-2
The Scrypt function
Last updated 2 years ago