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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 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 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.

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

     HMAC_cleanup() 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:

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

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

     HMAC_Final() 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.

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



CONFORMING TO
     RFC 2104



SEE ALSO
     sha(3), evp(3)



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









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Created 1996-2024 by Maxim Chirkov

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