HMAC_Init man page on DigitalUNIX

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HMAC(3)								       HMAC(3)

NAME
       HMAC,  HMAC_Init,  HMAC_Update, HMAC_Final, HMAC_cleanup - HMAC message
       authentication code

SYNOPSIS
       #include <openssl/hmac.h>

       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 );
       void HMAC_Init(
	       HMAC_CTX *ctx, const void *key, int key_len, const  EVP_MD  *md
       ); void HMAC_Update(
	       HMAC_CTX	 *ctx,	const  unsigned	 char  *data,  int len ); void
       HMAC_Final(
	       HMAC_CTX *ctx, unsigned char *md, unsigned  int	*len  );  void
       HMAC_cleanup(
	       HMAC_CTX *ctx );

DESCRIPTION
       HMAC is a message authentication code (MAC), i.e. a keyed hash function
       used for message authentication, which is based on a hash function.

       The HMAC() function computes the message authentication code of	the  n
       bytes  at  d  using  the	 hash function evp_md and the key key which is
       key_len bytes long.

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

       The  evp_md can be EVP_sha1(), EVP_ripemd160(), etc. The key and evp_md
       can be NULL if a key and hash function have been set in a previous call
       to HMAC_Init() for that HMAC_CTX.

       The  HMAC_cleanup()  function  erases  the  key and other data from the
       HMAC_CTX.

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

       The  HMAC_Init()	 function  initializes a HMAC_CTX structure to use the
       hash function evp_md and the key key which is key_len bytes long.

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

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

       HMAC conforms to RFC 2104.

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

       The HMAC_Init(), HMAC_Update(), HMAC_Final(), and HMAC_cleanup() do not
       return values.

HISTORY
       The   HMAC(),	HMAC_Init(),	HMAC_Update(),	  HMAC_Final(),	   and
       HMAC_cleanup() functions are available since SSLeay 0.9.0.

SEE ALSO
       Functions: sha(3), evp(3)

								       HMAC(3)
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