OpenSL                                            hmac(3openssl)



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 HMACTXinit(HMACTX *ctx);

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

      void HMACTXcleanup(HMACTX *ctx);
      void HMACcleanup(HMACTX *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 n
     bytes at d using the hash function evpmd and the key key
     which is keylen bytes long.

     It places the result in md (which must have space for the
     output of the hash function, which is no more than
     EVPMAXMDSIZE bytes).  If md is NUL, the digest is placed
     in a static array.  The size of the output is placed in
     mdlen, unless it is NUL.

     evpmd can be EVPsha1(), EVPripemd160() etc.  key and
     evpmd may be NUL if a key and hash function have been set
     in a previous call to HMACInit() for that HMACTX.

     HMACTXinit() initialises a HMACTX before first use. It
     must be called.

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

     HMACcleanup() is an alias for HMACTXcleanup() included
     for back compatibility with 0.9.6b, it is deprecated.




OpenSL-0.9.8       Last change: Oct 11 2005                    1






OpenSL                                            hmac(3openssl)



     The following functions may be used if the message is not
     completely stored in memory:

     HMACInit() initializes a HMACTX structure to use the hash
     function evpmd and the key key which is keylen bytes long.
     It is deprecated and only included for backward
     compatibility with OpenSL 0.9.6b.

     HMACInitex() initializes or reuses a HMACTX structure to
     use the function evpmd and key key. Either can be NUL, in
     which case the existing one will be reused. HMACTXinit()
     must have been called before the first use of an HMACTX in
     this function. N.B. HMACInit() had this undocumented
     behaviour in previous versions of OpenSL - failure to
     switch to HMACInitex() in programs that expect it will
     cause them to stop working.

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

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

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

     HMACTXinit(), HMACInitex(), HMACUpdate(), HMACFinal()
     and HMACTXcleanup() do not return values.

CONFORMING TO
     RFC 2104

SEE ALSO
     sha(3), evp(3)

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

     HMACTXinit(), HMACInitex() and HMACTXcleanup() are
     available since OpenSL 0.9.7.














OpenSL-0.9.8       Last change: Oct 11 2005                    2