=pod =head1 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 =head1 SYNOPSIS #include Deprecated since OpenSSL 3.0, can be hidden entirely by defining B with a suitable version value, see L: 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); 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, int 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); Deprecated since OpenSSL 1.1.0, can be hidden entirely by defining B with a suitable version value, see L: int HMAC_Init(HMAC_CTX *ctx, const void *key, int key_len, const EVP_MD *md); =head1 DESCRIPTION All of the functions described on this page are deprecated. Applications should instead use L, L, L, L and L. 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 B bytes at B using the hash function B and the key B which is B bytes long. It places the result in B (which must have space for the output of the hash function, which is no more than B bytes). If B is NULL, the digest is placed in a static array. The size of the output is placed in B, unless it is B. Note: passing a NULL value for B to use the static array is not thread safe. B 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_CTX_new() creates a new HMAC_CTX in heap memory. HMAC_CTX_reset() clears an existing B 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 B, releases any associated resources and finally frees the B itself. The following functions may be used if the message is not completely stored in memory: HMAC_Init_ex() initializes or reuses a B structure to use the hash function B and key B. If both are NULL, or if B is NULL and B is the same as the previous call, then the existing key is reused. B must have been created with HMAC_CTX_new() before the first use of an B in this function. If HMAC_Init_ex() is called with B NULL and B is not the same as the previous digest used by B then an error is returned because reuse of an existing key with a different digest is not supported. HMAC_Init() initializes a B structure to use the hash function B and the key B which is B bytes long. HMAC_Update() can be called repeatedly with chunks of the message to be authenticated (B bytes at B). HMAC_Final() places the message authentication code in B, which must have space for the hash function output. HMAC_CTX_copy() copies all of the internal state from B into B. HMAC_CTX_set_flags() applies the specified flags to the internal EVP_MD_CTXs. These flags have the same meaning as for L. 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. =head1 RETURN VALUES HMAC() returns a pointer to the message authentication code or NULL if an error occurred. HMAC_CTX_new() returns a pointer to a new B on success or B 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. =head1 CONFORMING TO RFC 2104 =head1 SEE ALSO L, L =head1 HISTORY All of these functions 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. =head1 COPYRIGHT Copyright 2000-2016 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 L. =cut