HMAC(3ossl) OpenSSL HMAC(3ossl)
NAME
HMAC, HMAC_CTX_new, HMAC_CTX_reset, HMAC_CTX_free, HMAC_Init,
HMAC_Init_ex, HMAC_Update, HMAC_Final, HMAC_CTX_copy,
HMAC_CTX_set_flags, HMAC_CTX_get_md, HMAC_size - 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 *data, size_t data_len,
unsigned char *md, unsigned int *md_len);
The following functions have been deprecated since OpenSSL 3.0, and can
be hidden entirely by defining OPENSSL_API_COMPAT with a suitable
version value, see openssl_user_macros(7):
HMAC_CTX *HMAC_CTX_new(void);
int HMAC_CTX_reset(HMAC_CTX *ctx);
int HMAC_Init_ex(HMAC_CTX *ctx, const void *key, int key_len,
const EVP_MD *md, ENGINE *impl);
int HMAC_Update(HMAC_CTX *ctx, const unsigned char *data, size_t len);
int HMAC_Final(HMAC_CTX *ctx, unsigned char *md, unsigned int *len);
void HMAC_CTX_free(HMAC_CTX *ctx);
int HMAC_CTX_copy(HMAC_CTX *dctx, HMAC_CTX *sctx);
void HMAC_CTX_set_flags(HMAC_CTX *ctx, unsigned long flags);
const EVP_MD *HMAC_CTX_get_md(const HMAC_CTX *ctx);
size_t HMAC_size(const HMAC_CTX *e);
The following function has been deprecated since OpenSSL 1.1.0, and can
be hidden entirely by defining OPENSSL_API_COMPAT with a suitable
version value, see openssl_user_macros(7):
int HMAC_Init(HMAC_CTX *ctx, const void *key, int key_len,
const EVP_MD *md);
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(3) computes the message authentication code of the data_len bytes
at data using the hash function evp_md and the key key which is key_len
bytes long. The key may also be NULL with key_len being 0.
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. Note: passing a NULL value for
md to use the static array is not thread safe.
evp_md is a message digest such as EVP_sha1(), EVP_ripemd160() etc.
HMAC does not support variable output length digests such as
EVP_shake128() and EVP_shake256().
HMAC(3) uses the default OSSL_LIB_CTX. Use EVP_Q_mac(3) instead if a
library context is required.
All of the functions described below are deprecated. Applications
should instead use EVP_MAC_CTX_new(3), EVP_MAC_CTX_free(3),
EVP_MAC_init(3), EVP_MAC_update(3) and EVP_MAC_final(3) or the 'quick'
single-shot MAC function EVP_Q_mac(3).
HMAC_CTX_new() creates a new HMAC_CTX in heap memory.
HMAC_CTX_reset() clears an existing HMAC_CTX and associated resources,
making it suitable for new computations as if it was newly created with
HMAC_CTX_new().
HMAC_CTX_free() erases the key and other data from the HMAC_CTX,
releases any associated resources and finally frees the HMAC_CTX
itself. If the argument is NULL, nothing is done.
The following functions may be used if the message is not completely
stored in memory:
HMAC_Init_ex() initializes or reuses a HMAC_CTX structure to use the
hash function evp_md and key key. If both are NULL, or if key is NULL
and evp_md is the same as the previous call, then the existing key is
reused. ctx must have been created with HMAC_CTX_new() before the first
use of an HMAC_CTX in this function.
If HMAC_Init_ex() is called with key NULL and evp_md is not the same as
the previous digest used by ctx then an error is returned because reuse
of an existing key with a different digest is not supported.
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.
HMAC_CTX_copy() copies all of the internal state from sctx into dctx.
HMAC_CTX_set_flags() applies the specified flags to the internal
EVP_MD_CTXs. These flags have the same meaning as for
EVP_MD_CTX_set_flags(3).
HMAC_CTX_get_md() returns the EVP_MD that has previously been set for
the supplied HMAC_CTX.
HMAC_size() returns the length in bytes of the underlying hash function
output.
RETURN VALUES
HMAC(3) returns a pointer to the message authentication code or NULL if
an error occurred.
HMAC_CTX_new() returns a pointer to a new HMAC_CTX on success or NULL
if an error occurred.
HMAC_CTX_reset(), HMAC_Init_ex(), HMAC_Update(), HMAC_Final() and
HMAC_CTX_copy() return 1 for success or 0 if an error occurred.
HMAC_CTX_get_md() return the EVP_MD previously set for the supplied
HMAC_CTX or NULL if no EVP_MD has been set.
HMAC_size() returns the length in bytes of the underlying hash function
output or zero on error.
CONFORMING TO
RFC 2104
SEE ALSO
SHA1(3), EVP_Q_mac(3), evp(7)
HISTORY
All functions except for HMAC(3) were deprecated in OpenSSL 3.0.
HMAC_CTX_init() was replaced with HMAC_CTX_reset() in OpenSSL 1.1.0.
HMAC_CTX_cleanup() existed in OpenSSL before version 1.1.0.
HMAC_CTX_new(), HMAC_CTX_free() and HMAC_CTX_get_md() are new in
OpenSSL 1.1.0.
HMAC_Init_ex(), HMAC_Update() and HMAC_Final() did not return values in
OpenSSL before version 1.0.0.
COPYRIGHT
Copyright 2000-2024 The OpenSSL Project Authors. All Rights Reserved.
Licensed under the Apache License 2.0 (the "License"). You may not use
this file except in compliance with the License. You can obtain a copy
in the file LICENSE in the source distribution or at
<https://www.openssl.org/source/license.html>.
3.3.2 2024-09-04 HMAC(3ossl)
openssl 3.3.2 - Generated Sun Sep 15 15:27:33 CDT 2024