hmac(3) OpenSSL hmac(3)

NAME
       HMAC, HMACInit, HMACUpdate, HMACFinal, HMACcleanup - HMAC message
       authentication code

SYNOPSIS
        #include 

        unsigned char *HMAC(const EVPMD *evpmd, const void *key,
                      int keylen, const unsigned char *d, int n,
                      unsigned char *md, unsigned int *mdlen);

        void HMACCTXinit(HMACCTX *ctx);

        void HMACInit(HMACCTX *ctx, const void *key, int keylen,
                      const EVPMD *md);
        void HMACInitex(HMACCTX *ctx, const void *key, int keylen,
                          const EVPMD *md, ENGINE *impl);
        void HMACUpdate(HMACCTX *ctx, const unsigned char *data, int len);
        void HMACFinal(HMACCTX *ctx, unsigned char *md, unsigned int *len);

        void HMACCTXcleanup(HMACCTX *ctx);
        void HMACcleanup(HMACCTX *ctx);

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 nn bytes at dd
       using the hash function eevvppmmdd and the key kkeeyy which is kkeeyylleenn bytes
       long.

       It places the result in mmdd (which must have space for the output of the
       hash function, which is no more than EEVVPPMMAAXXMMDDSSIIZZEE bytes).  If mmdd is
       NULL, the digest is placed in a static array.  The size of the output
       is placed in mmddlleenn, unless it is NNUULLLL.

       eevvppmmdd can be EVPsha1(), EVPripemd160() etc.  kkeeyy and eevvppmmdd may be
       NNUULLLL if a key and hash function have been set in a previous call to
       HMACInit() for that HHMMAACCCCTTXX.

       HMACCTXinit() initialises a HHMMAACCCCTTXX before first use. It must be
       called.

       HMACCTXcleanup() erases the key and other data from the HHMMAACCCCTTXX and
       releases any associated resources. It must be called when an HHMMAACCCCTTXX
       is no longer required.

       HMACcleanup() is an alias for HMACCTXcleanup() 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:

       HMACInit() initializes a HHMMAACCCCTTXX structure to use the hash function
       eevvppmmdd and the key kkeeyy which is kkeeyylleenn bytes long. It is deprecated
       and only included for backward compatibility with OpenSSL 0.9.6b.

       HMACInitex() initializes or reuses a HHMMAACCCCTTXX structure to use the
       function eevvppmmdd and key kkeeyy. Either can be NULL, in which case the
       existing one will be reused. HMACCTXinit() must have been called
       before the first use of an HHMMAACCCCTTXX in this function. NN..BB.. HHMMAACCIInniitt(())
       hhaadd tthhiiss uunnddooccuummeenntteedd bbeehhaavviioouurr iinn pprreevviioouuss vveerrssiioonnss ooff OOppeennSSSSLL -
       ffaaiilluurree ttoo sswwiittcchh ttoo HHMMAACCIInniitteexx(()) iinn pprrooggrraammss tthhaatt eexxppeecctt iitt wwiillll
       ccaauussee tthheemm ttoo ssttoopp wwoorrkkiinngg.

       HMACUpdate() can be called repeatedly with chunks of the message to be
       authenticated (lleenn bytes at ddaattaa).

       HMACFinal() places the message authentication code in mmdd, which must
       have space for the hash function output.

RETURN VALUES
       HMAC() returns a pointer to the message authentication code.

       HMACCTXinit(), HMACInitex(), HMACUpdate(), HMACFinal() and
       HMACCTXcleanup() do not return values.

CCOONNFFOORRMMIINNGG TTOO
       RFC 2104

SEE ALSO
       sha(3), evp(3)

HISTORY       HMAC(), HMACInit(), HMACUpdate(), HMACFinal() and HMACcleanup() are
       available since SSLeay 0.9.0.

       HMACCTXinit(), HMACInitex() and HMACCTXcleanup() are available
       since OpenSSL 0.9.7.



0.9.7l                            2006-01-30                           hmac(3)