1=pod 2 3=head1 NAME 4 5HMAC, 6HMAC_CTX_new, 7HMAC_CTX_reset, 8HMAC_CTX_free, 9HMAC_Init, 10HMAC_Init_ex, 11HMAC_Update, 12HMAC_Final, 13HMAC_CTX_copy, 14HMAC_CTX_set_flags, 15HMAC_CTX_get_md, 16HMAC_size 17- HMAC message authentication code 18 19=head1 SYNOPSIS 20 21 #include <openssl/hmac.h> 22 23 unsigned char *HMAC(const EVP_MD *evp_md, const void *key, 24 int key_len, const unsigned char *d, int n, 25 unsigned char *md, unsigned int *md_len); 26 27 HMAC_CTX *HMAC_CTX_new(void); 28 int HMAC_CTX_reset(HMAC_CTX *ctx); 29 30 int HMAC_Init_ex(HMAC_CTX *ctx, const void *key, int key_len, 31 const EVP_MD *md, ENGINE *impl); 32 int HMAC_Update(HMAC_CTX *ctx, const unsigned char *data, int len); 33 int HMAC_Final(HMAC_CTX *ctx, unsigned char *md, unsigned int *len); 34 35 void HMAC_CTX_free(HMAC_CTX *ctx); 36 37 int HMAC_CTX_copy(HMAC_CTX *dctx, HMAC_CTX *sctx); 38 void HMAC_CTX_set_flags(HMAC_CTX *ctx, unsigned long flags); 39 const EVP_MD *HMAC_CTX_get_md(const HMAC_CTX *ctx); 40 41 size_t HMAC_size(const HMAC_CTX *e); 42 43Deprecated: 44 45 #if OPENSSL_API_COMPAT < 0x10100000L 46 int HMAC_Init(HMAC_CTX *ctx, const void *key, int key_len, 47 const EVP_MD *md); 48 #endif 49 50=head1 DESCRIPTION 51 52HMAC is a MAC (message authentication code), i.e. a keyed hash 53function used for message authentication, which is based on a hash 54function. 55 56HMAC() computes the message authentication code of the B<n> bytes at 57B<d> using the hash function B<evp_md> and the key B<key> which is 58B<key_len> bytes long. 59 60It places the result in B<md> (which must have space for the output of 61the hash function, which is no more than B<EVP_MAX_MD_SIZE> bytes). 62If B<md> is NULL, the digest is placed in a static array. The size of 63the output is placed in B<md_len>, unless it is B<NULL>. Note: passing a NULL 64value for B<md> to use the static array is not thread safe. 65 66B<evp_md> can be EVP_sha1(), EVP_ripemd160() etc. 67 68HMAC_CTX_new() creates a new HMAC_CTX in heap memory. 69 70HMAC_CTX_reset() zeroes an existing B<HMAC_CTX> and associated 71resources, making it suitable for new computations as if it was newly 72created with HMAC_CTX_new(). 73 74HMAC_CTX_free() erases the key and other data from the B<HMAC_CTX>, 75releases any associated resources and finally frees the B<HMAC_CTX> 76itself. 77 78The following functions may be used if the message is not completely 79stored in memory: 80 81HMAC_Init_ex() initializes or reuses a B<HMAC_CTX> structure to use the hash 82function B<evp_md> and key B<key>. If both are NULL, or if B<key> is NULL 83and B<evp_md> is the same as the previous call, then the 84existing key is 85reused. B<ctx> must have been created with HMAC_CTX_new() before the first use 86of an B<HMAC_CTX> in this function. 87 88If HMAC_Init_ex() is called with B<key> NULL and B<evp_md> is not the 89same as the previous digest used by B<ctx> then an error is returned 90because reuse of an existing key with a different digest is not supported. 91 92HMAC_Init() initializes a B<HMAC_CTX> structure to use the hash 93function B<evp_md> and the key B<key> which is B<key_len> bytes 94long. 95 96HMAC_Update() can be called repeatedly with chunks of the message to 97be authenticated (B<len> bytes at B<data>). 98 99HMAC_Final() places the message authentication code in B<md>, which 100must have space for the hash function output. 101 102HMAC_CTX_copy() copies all of the internal state from B<sctx> into B<dctx>. 103 104HMAC_CTX_set_flags() applies the specified flags to the internal EVP_MD_CTXs. 105These flags have the same meaning as for L<EVP_MD_CTX_set_flags(3)>. 106 107HMAC_CTX_get_md() returns the EVP_MD that has previously been set for the 108supplied HMAC_CTX. 109 110HMAC_size() returns the length in bytes of the underlying hash function output. 111 112=head1 RETURN VALUES 113 114HMAC() returns a pointer to the message authentication code or NULL if 115an error occurred. 116 117HMAC_CTX_new() returns a pointer to a new B<HMAC_CTX> on success or 118B<NULL> if an error occurred. 119 120HMAC_CTX_reset(), HMAC_Init_ex(), HMAC_Update(), HMAC_Final() and 121HMAC_CTX_copy() return 1 for success or 0 if an error occurred. 122 123HMAC_CTX_get_md() return the EVP_MD previously set for the supplied HMAC_CTX or 124NULL if no EVP_MD has been set. 125 126HMAC_size() returns the length in bytes of the underlying hash function output 127or zero on error. 128 129=head1 CONFORMING TO 130 131RFC 2104 132 133=head1 SEE ALSO 134 135L<SHA1(3)>, L<evp(7)> 136 137=head1 HISTORY 138 139HMAC_CTX_init() was replaced with HMAC_CTX_reset() in OpenSSL 1.1.0. 140 141HMAC_CTX_cleanup() existed in OpenSSL before version 1.1.0. 142 143HMAC_CTX_new(), HMAC_CTX_free() and HMAC_CTX_get_md() are new in OpenSSL 1.1.0. 144 145HMAC_Init_ex(), HMAC_Update() and HMAC_Final() did not return values in 146OpenSSL before version 1.0.0. 147 148=head1 COPYRIGHT 149 150Copyright 2000-2019 The OpenSSL Project Authors. All Rights Reserved. 151 152Licensed under the OpenSSL license (the "License"). You may not use 153this file except in compliance with the License. You can obtain a copy 154in the file LICENSE in the source distribution or at 155L<https://www.openssl.org/source/license.html>. 156 157=cut 158