text: /* Copyright (C) 1995-1998 Eric Young (eay@cryptsoft.com)
   * All rights reserved.
   *
   * This package is an SSL implementation written
   * by Eric Young (eay@cryptsoft.com).
   * The implementation was written so as to conform with Netscapes SSL.
   *
   * This library is free for commercial and non-commercial use as long as
   * the following conditions are aheared to.  The following conditions
   * apply to all code found in this distribution, be it the RC4, RSA,
   * lhash, DES, etc., code; not just the SSL code.  The SSL documentation
   * included with this distribution is covered by the same copyright terms
   * except that the holder is Tim Hudson (tjh@cryptsoft.com).
   *
   * Copyright remains Eric Young's, and as such any Copyright notices in
   * the code are not to be removed.
   * If this package is used in a product, Eric Young should be given attribution
   * as the author of the parts of the library used.
   * This can be in the form of a textual message at program startup or
   * in documentation (online or textual) provided with the package.
   *
   * Redistribution and use in source and binary forms, with or without
   * modification, are permitted provided that the following conditions
   * are met:
   * 1. Redistributions of source code must retain the copyright
   *    notice, this list of conditions and the following disclaimer.
   * 2. Redistributions in binary form must reproduce the above copyright
   *    notice, this list of conditions and the following disclaimer in the
   *    documentation and/or other materials provided with the distribution.
   * 3. All advertising materials mentioning features or use of this software
   *    must display the following acknowledgement:
   *    "This product includes cryptographic software written by
   *     Eric Young (eay@cryptsoft.com)"
   *    The word 'cryptographic' can be left out if the rouines from the library
   *    being used are not cryptographic related :-).
   * 4. If you include any Windows specific code (or a derivative thereof) from
   *    the apps directory (application code) you must include an acknowledgement:
   *    "This product includes software written by Tim Hudson (tjh@cryptsoft.com)"
   *
   * THIS SOFTWARE IS PROVIDED BY ERIC YOUNG ``AS IS'' AND
   * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
   * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   * SUCH DAMAGE.
   *
   * The licence and distribution terms for any publically available version or
   * derivative of this code cannot be changed.  i.e. this code cannot simply be
   * copied and put under another distribution licence
   * [including the GNU Public Licence.] */
  
  #ifndef OPENSSL_HEADER_HMAC_H
  #define OPENSSL_HEADER_HMAC_H
  
  #include <openssl/base.h>
  
  #include <openssl/digest.h>
  
  #if defined(__cplusplus)
  extern "C" {
  #endif
  
  
  /* HMAC contains functions for constructing PRFs from Merkle–Damgård hash
   * functions using HMAC. */
  
  
  /* One-shot operation. */
  
  /* HMAC calculates the HMAC of |data_len| bytes of |data|, using the given key
   * and hash function, and writes the result to |out|. On entry, |out| must
   * contain at least |EVP_MD_size| bytes of space. The actual length of the
   * result is written to |*out_len|. An output size of |EVP_MAX_MD_SIZE| will
   * always be large enough. It returns |out| or NULL on error. */
  OPENSSL_EXPORT uint8_t *HMAC(const EVP_MD *evp_md, const void *key,
                               size_t key_len, const uint8_t *data,
                               size_t data_len, uint8_t *out,
                               unsigned int *out_len);
  
  
  /* Incremental operation. */
  
  /* HMAC_CTX_init initialises |ctx| for use in an HMAC operation. It's assumed
   * that HMAC_CTX objects will be allocated on the stack thus no allocation
   * function is provided. If needed, allocate |sizeof(HMAC_CTX)| and call
   * |HMAC_CTX_init| on it. */
  OPENSSL_EXPORT void HMAC_CTX_init(HMAC_CTX *ctx);
  
  /* HMAC_CTX_cleanup frees data owned by |ctx|. */
  OPENSSL_EXPORT void HMAC_CTX_cleanup(HMAC_CTX *ctx);
  
  /* HMAC_Init_ex sets up an initialised |HMAC_CTX| to use |md| as the hash
   * function and |key| as the key. For a non-initial call, |md| may be NULL, in
   * which case the previous hash function will be used. If the hash function has
   * not changed and |key| is NULL, |ctx| reuses the previous key. It returns one
   * on success or zero otherwise.
   *
   * WARNING: NULL and empty keys are ambiguous on non-initial calls. Passing NULL
   * |key| but repeating the previous |md| reuses the previous key rather than the
   * empty key. */
  OPENSSL_EXPORT int HMAC_Init_ex(HMAC_CTX *ctx, const void *key, size_t key_len,
                                  const EVP_MD *md, ENGINE *impl);
  
  /* HMAC_Update hashes |data_len| bytes from |data| into the current HMAC
   * operation in |ctx|. It returns one. */
  OPENSSL_EXPORT int HMAC_Update(HMAC_CTX *ctx, const uint8_t *data,
                                 size_t data_len);
  
  /* HMAC_Final completes the HMAC operation in |ctx| and writes the result to
   * |out| and the sets |*out_len| to the length of the result. On entry, |out|
   * must contain at least |HMAC_size| bytes of space. An output size of
   * |EVP_MAX_MD_SIZE| will always be large enough. It returns one on success or
   * zero on error. */
  OPENSSL_EXPORT int HMAC_Final(HMAC_CTX *ctx, uint8_t *out,
                                unsigned int *out_len);
  
  
  /* Utility functions. */
  
  /* HMAC_size returns the size, in bytes, of the HMAC that will be produced by
   * |ctx|. On entry, |ctx| must have been setup with |HMAC_Init_ex|. */
  OPENSSL_EXPORT size_t HMAC_size(const HMAC_CTX *ctx);
  
  /* HMAC_CTX_copy_ex sets |dest| equal to |src|. On entry, |dest| must have been
   * initialised by calling |HMAC_CTX_init|. It returns one on success and zero
   * on error. */
  OPENSSL_EXPORT int HMAC_CTX_copy_ex(HMAC_CTX *dest, const HMAC_CTX *src);
  
  
  /* Deprecated functions. */
  
  OPENSSL_EXPORT int HMAC_Init(HMAC_CTX *ctx, const void *key, int key_len,
                               const EVP_MD *md);
  
  /* HMAC_CTX_copy calls |HMAC_CTX_init| on |dest| and then sets it equal to
   * |src|. On entry, |dest| must /not/ be initialised for an operation with
   * |HMAC_Init_ex|. It returns one on success and zero on error. */
  OPENSSL_EXPORT int HMAC_CTX_copy(HMAC_CTX *dest, const HMAC_CTX *src);
  
  
  /* Private functions */
  
  struct hmac_ctx_st {
    const EVP_MD *md;
    EVP_MD_CTX md_ctx;
    EVP_MD_CTX i_ctx;
    EVP_MD_CTX o_ctx;
  } /* HMAC_CTX */;
  
  
  #if defined(__cplusplus)
  }  /* extern C */
  #endif
  
  #endif  /* OPENSSL_HEADER_HMAC_H */
  