hmac(3) OpenSSL hmac(3)NAME
HMAC, HMAC_Init, HMAC_Update, HMAC_Final, HMAC_cleanup - HMAC message
authentication code
SYNOPSIS
#include <openssl/hmac.h>
unsigned char *HMAC(const EVP_MD *evp_md, const void *key,
int key_len, const unsigned char *d, int n,
unsigned char *md, unsigned int *md_len);
void HMAC_Init(HMAC_CTX *ctx, const void *key, int key_len,
const EVP_MD *md);
void HMAC_Update(HMAC_CTX *ctx, const unsigned char *data, int len);
void HMAC_Final(HMAC_CTX *ctx, unsigned char *md, unsigned int *len);
void HMAC_cleanup(HMAC_CTX *ctx);
DESCRIPTION
HMAC is a MAC (message authentication code), i.e. a keyed hash function
used for message authentication, which is based on a hash function.
HMAC() computes the message authentication code of the n bytes at d
using the hash function evp_md and the key key which is key_len bytes
long.
It places the result in md (which must have space for the output of the
hash function, which is no more than EVP_MAX_MD_SIZE bytes). If md is
NULL, the digest is placed in a static array. The size of the output
is placed in md_len, unless it is NULL.
evp_md can be EVP_sha1(), EVP_ripemd160() etc. key and evp_md may be
NULL if a key and hash function have been set in a previous call to
HMAC_Init() for that HMAC_CTX.
HMAC_cleanup() erases the key and other data from the HMAC_CTX.
The following functions may be used if the message is not completely
stored in memory:
HMAC_Init() initializes a HMAC_CTX structure to use the hash function
evp_md and the key key which is key_len bytes long.
HMAC_Update() can be called repeatedly with chunks of the message to be
authenticated (len bytes at data).
HMAC_Final() places the message authentication code in md, which must
have space for the hash function output.
RETURN VALUESHMAC() returns a pointer to the message authentication code.
HMAC_Init(), HMAC_Update(), HMAC_Final() and HMAC_cleanup() do not
return values.
CONFORMING TO
RFC 2104
SEE ALSOsha(3), evp(3)HISTORYHMAC(), HMAC_Init(), HMAC_Update(), HMAC_Final() and HMAC_cleanup() are
available since SSLeay 0.9.0.
3rd Berkeley Distribution 0.9.6m hmac(3)
