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HMAC(3) OpenSSL HMAC(3)
NNAAMMEE
HMAC, HMAC_Init, HMAC_Update, HMAC_Final, HMAC_cleanup -
HMAC message authentication code
SSYYNNOOPPSSIISS
#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);
DDEESSCCRRIIPPTTIIOONN
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 nn
bytes at dd using the hash function eevvpp__mmdd and the key kkeeyy
which is kkeeyy__lleenn bytes long.
It places the result in mmdd (which must have space for the
output of the hash function, which is no more than
EEVVPP__MMAAXX__MMDD__SSIIZZEE bytes). If mmdd is NULL, the digest is
placed in a static array. The size of the output is
placed in mmdd__lleenn, unless it is NNUULLLL.
eevvpp__mmdd can be EVP_sha1(), EVP_ripemd160() etc. kkeeyy and
eevvpp__mmdd may be NNUULLLL if a key and hash function have been
set in a previous call to HMAC_Init() for that HHMMAACC__CCTTXX.
HMAC_cleanup() erases the key and other data from the
HHMMAACC__CCTTXX.
The following functions may be used if the message is not
completely stored in memory:
HMAC_Init() initializes a HHMMAACC__CCTTXX structure to use the
hash function eevvpp__mmdd and the key kkeeyy which is kkeeyy__lleenn
bytes long.
HMAC_Update() can be called repeatedly with chunks of the
message to be authenticated (lleenn bytes at ddaattaa).
HMAC_Final() places the message authentication code in mmdd,
which must have space for the hash function output.
2001-04-28 OpenBSD 2.9 1
HMAC(3) OpenSSL HMAC(3)
RREETTUURRNN VVAALLUUEESS
HMAC() returns a pointer to the message authentication
code.
HMAC_Init(), HMAC_Update(), HMAC_Final() and
HMAC_cleanup() do not return values.
CCOONNFFOORRMMIINNGG TTOO
RFC 2104
SSEEEE AALLSSOO
SHA1(3), EVP_DigestInit(3)
HHIISSTTOORRYY
HMAC(), HMAC_Init(), HMAC_Update(), HMAC_Final() and
HMAC_cleanup() are available since SSLeay 0.9.0.
2001-04-28 OpenBSD 2.9 2
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