HMAC, HMAC_CTX_init, HMAC_Init, HMAC_Init_ex, HMAC_Update, HMAC_Final,
HMAC_CTX_cleanup, HMAC_cleanup - HMAC message authentication code
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_CTX_init(HMAC_CTX *ctx);
int HMAC_Init(HMAC_CTX *ctx, const void *key, int key_len,
const EVP_MD *md);
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, int len);
int HMAC_Final(HMAC_CTX *ctx, unsigned char *md, unsigned int *len);
void HMAC_CTX_cleanup(HMAC_CTX *ctx);
void HMAC_cleanup(HMAC_CTX *ctx);
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
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 can be EVP_sha1(), EVP_ripemd160() etc.
HMAC_CTX_init() initialises a HMAC_CTX before first use. It must be
HMAC_CTX_cleanup() erases the key and other data from the HMAC_CTX and
releases any associated resources. It must be called when an HMAC_CTX
is no longer required.
HMAC_cleanup() is an alias for HMAC_CTX_cleanup() included for back
compatibility with 0.9.6b, it is deprecated.
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. It is deprecated
and only included for backward compatibility with OpenSSL 0.9.6b.
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 evp_md is the
same as the previous digest used by ctx and key is NULL) 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. N.B. HHMMAACC_IInniitt(()) had
this undocumented behaviour in previous versions of OpenSSL - failure
to switch to HHMMAACC_IInniitt_eexx(()) in programs that expect it will cause them
to stop working.
NB: if HHMMAACC_IInniitt_eexx(()) 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 sup-
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() returns a pointer to the message authentication code or NULL if
an error occurred.
HMAC_Init_ex(), HMAC_Update() and HMAC_Final() return 1 for success or
0 if an error occurred.
HMAC_CTX_init() and HMAC_CTX_cleanup() do not return values.
HMAC(), HMAC_Init(), HMAC_Update(), HMAC_Final() and HMAC_cleanup() are
available since SSLeay 0.9.0.
HMAC_CTX_init(), HMAC_Init_ex() and HMAC_CTX_cleanup() are available
since OpenSSL 0.9.7.
HMAC_Init_ex(), HMAC_Update() and HMAC_Final() did not return values in
versions of OpenSSL before 1.0.0.
1.0.2t 2019-09-10 hmac(3)
Man(1) output converted with