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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)

Index for Section 3

Alphabetical listing for H

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