1=pod 2 3=head1 NAME 4 5HMAC, HMAC_Init, HMAC_Update, HMAC_Final, HMAC_cleanup - HMAC message 6authentication code 7 8=head1 SYNOPSIS 9 10 #include <openssl/hmac.h> 11 12 unsigned char *HMAC(const EVP_MD *evp_md, const void *key, 13 int key_len, const unsigned char *d, int n, 14 unsigned char *md, unsigned int *md_len); 15 16 void HMAC_CTX_init(HMAC_CTX *ctx); 17 18 void HMAC_Init(HMAC_CTX *ctx, const void *key, int key_len, 19 const EVP_MD *md); 20 void HMAC_Init_ex(HMAC_CTX *ctx, const void *key, int key_len, 21 const EVP_MD *md, ENGINE *impl); 22 void HMAC_Update(HMAC_CTX *ctx, const unsigned char *data, int len); 23 void HMAC_Final(HMAC_CTX *ctx, unsigned char *md, unsigned int *len); 24 25 void HMAC_CTX_cleanup(HMAC_CTX *ctx); 26 void HMAC_cleanup(HMAC_CTX *ctx); 27 28=head1 DESCRIPTION 29 30HMAC is a MAC (message authentication code), i.e. a keyed hash 31function used for message authentication, which is based on a hash 32function. 33 34HMAC() computes the message authentication code of the B<n> bytes at 35B<d> using the hash function B<evp_md> and the key B<key> which is 36B<key_len> bytes long. 37 38It places the result in B<md> (which must have space for the output of 39the hash function, which is no more than B<EVP_MAX_MD_SIZE> bytes). 40If B<md> is NULL, the digest is placed in a static array. The size of 41the output is placed in B<md_len>, unless it is B<NULL>. 42 43B<evp_md> can be EVP_sha1(), EVP_ripemd160() etc. 44 45HMAC_CTX_init() initialises a B<HMAC_CTX> before first use. It must be 46called. 47 48HMAC_CTX_cleanup() erases the key and other data from the B<HMAC_CTX> 49and releases any associated resources. It must be called when an 50B<HMAC_CTX> is no longer required. 51 52HMAC_cleanup() is an alias for HMAC_CTX_cleanup() included for back 53compatibility with 0.9.6b, it is deprecated. 54 55The following functions may be used if the message is not completely 56stored in memory: 57 58HMAC_Init() initializes a B<HMAC_CTX> structure to use the hash 59function B<evp_md> and the key B<key> which is B<key_len> bytes 60long. It is deprecated and only included for backward compatibility 61with OpenSSL 0.9.6b. 62 63HMAC_Init_ex() initializes or reuses a B<HMAC_CTX> structure to use 64the function B<evp_md> and key B<key>. Either can be NULL, in which 65case the existing one will be reused. HMAC_CTX_init() must have been 66called before the first use of an B<HMAC_CTX> in this 67function. B<N.B. HMAC_Init() had this undocumented behaviour in 68previous versions of OpenSSL - failure to switch to HMAC_Init_ex() in 69programs that expect it will cause them to stop working>. 70 71HMAC_Update() can be called repeatedly with chunks of the message to 72be authenticated (B<len> bytes at B<data>). 73 74HMAC_Final() places the message authentication code in B<md>, which 75must have space for the hash function output. 76 77=head1 RETURN VALUES 78 79HMAC() returns a pointer to the message authentication code. 80 81HMAC_CTX_init(), HMAC_Init_ex(), HMAC_Update(), HMAC_Final() and 82HMAC_CTX_cleanup() do not return values. 83 84=head1 CONFORMING TO 85 86RFC 2104 87 88=head1 SEE ALSO 89 90L<sha(3)|sha(3)>, L<evp(3)|evp(3)> 91 92=head1 HISTORY 93 94HMAC(), HMAC_Init(), HMAC_Update(), HMAC_Final() and HMAC_cleanup() 95are available since SSLeay 0.9.0. 96 97HMAC_CTX_init(), HMAC_Init_ex() and HMAC_CTX_cleanup() are available 98since OpenSSL 0.9.7. 99 100=cut 101