=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 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: #if OPENSSL_API_COMPAT < 0x10100000L int HMAC_Init(HMAC_CTX *ctx, const void *key, int key_len, const EVP_MD *md); #endif =head1 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 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 can be EVP_sha1(), EVP_ripemd160() etc. HMAC_CTX_new() creates a new HMAC_CTX in heap memory. HMAC_CTX_reset() zeroes 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() initializes a B structure to use the hash function B and the key B which is B bytes long. It is deprecated and only included for backward compatibility with OpenSSL 0.9.6b. HMAC_Init_ex() initializes or reuses a B structure to use the hash function B and key B. If both are NULL (or B is the same as the previous digest used by B and B is NULL) the existing key is reused. B must have been created with HMAC_CTX_new() before the first use of an B in this function. B. B 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_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 HMAC_CTX_init() was replaced with HMAC_CTX_reset() in OpenSSL versions 1.1.0. HMAC_CTX_cleanup() existed in OpenSSL versions before 1.1.0. HMAC_CTX_new(), HMAC_CTX_free() and HMAC_CTX_get_md() are new in OpenSSL version 1.1.0. HMAC_Init_ex(), HMAC_Update() and HMAC_Final() did not return values in versions of OpenSSL before 1.0.0. =head1 COPYRIGHT Copyright 2000-2016 The OpenSSL Project Authors. All Rights Reserved. Licensed under the OpenSSL license (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