text: /**
   * \file sha256.h
   *
   * \brief This file contains SHA-224 and SHA-256 definitions and functions.
   *
   * The Secure Hash Algorithms 224 and 256 (SHA-224 and SHA-256) cryptographic
   * hash functions are defined in <em>FIPS 180-4: Secure Hash Standard (SHS)</em>.
   */
  /*
   *  Copyright The Mbed TLS Contributors
   *  SPDX-License-Identifier: Apache-2.0
   *
   *  Licensed under the Apache License, Version 2.0 (the "License"); you may
   *  not use this file except in compliance with the License.
   *  You may obtain a copy of the License at
   *
   *  http://www.apache.org/licenses/LICENSE-2.0
   *
   *  Unless required by applicable law or agreed to in writing, software
   *  distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
   *  WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   *  See the License for the specific language governing permissions and
   *  limitations under the License.
   */
  #ifndef MBEDTLS_SHA256_H
  #define MBEDTLS_SHA256_H
  
  #if !defined(MBEDTLS_CONFIG_FILE)
  #include "mbedtls/config.h"
  #else
  #include MBEDTLS_CONFIG_FILE
  #endif
  
  #include <stddef.h>
  #include <stdint.h>
  
  #define MBEDTLS_ERR_SHA256_BAD_INPUT_DATA -0x0074 /**< SHA-256 input data was malformed. */
  
  #ifdef __cplusplus
  extern "C" {
  #endif
  
  #if !defined(MBEDTLS_SHA256_ALT)
  // Regular implementation
  //
  
  /**
   * \brief          The SHA-256 context structure.
   *
   *                 The structure is used both for SHA-256 and for SHA-224
   *                 checksum calculations. The choice between these two is
   *                 made in the call to mbedtls_sha256_starts_ret().
   */
  typedef struct mbedtls_sha256_context {
      uint32_t total[2];        /*!< The number of Bytes processed.  */
      uint32_t state[8];        /*!< The intermediate digest state.  */
      unsigned char buffer[64]; /*!< The data block being processed. */
      int is224;                /*!< Determines which function to use:
                                       0: Use SHA-256, or 1: Use SHA-224. */
  } mbedtls_sha256_context;
  
  #else /* MBEDTLS_SHA256_ALT */
  #include "sha256_alt.h"
  #endif /* MBEDTLS_SHA256_ALT */
  
  /**
   * \brief          This function initializes a SHA-256 context.
   *
   * \param ctx      The SHA-256 context to initialize. This must not be \c NULL.
   */
  void mbedtls_sha256_init(mbedtls_sha256_context *ctx);
  
  /**
   * \brief          This function clears a SHA-256 context.
   *
   * \param ctx      The SHA-256 context to clear. This may be \c NULL, in which
   *                 case this function returns immediately. If it is not \c NULL,
   *                 it must point to an initialized SHA-256 context.
   */
  void mbedtls_sha256_free(mbedtls_sha256_context *ctx);
  
  /**
   * \brief          This function clones the state of a SHA-256 context.
   *
   * \param dst      The destination context. This must be initialized.
   * \param src      The context to clone. This must be initialized.
   */
  void mbedtls_sha256_clone(mbedtls_sha256_context *dst,
                            const mbedtls_sha256_context *src);
  
  /**
   * \brief          This function starts a SHA-224 or SHA-256 checksum
   *                 calculation.
   *
   * \param ctx      The context to use. This must be initialized.
   * \param is224    This determines which function to use. This must be
   *                 either \c 0 for SHA-256, or \c 1 for SHA-224.
   *
   * \return         \c 0 on success.
   * \return         A negative error code on failure.
   */
  int mbedtls_sha256_starts_ret(mbedtls_sha256_context *ctx, int is224);
  
  /**
   * \brief          This function feeds an input buffer into an ongoing
   *                 SHA-256 checksum calculation.
   *
   * \param ctx      The SHA-256 context. This must be initialized
   *                 and have a hash operation started.
   * \param input    The buffer holding the data. This must be a readable
   *                 buffer of length \p ilen Bytes.
   * \param ilen     The length of the input data in Bytes.
   *
   * \return         \c 0 on success.
   * \return         A negative error code on failure.
   */
  int mbedtls_sha256_update_ret(mbedtls_sha256_context *ctx,
                                const unsigned char *input,
                                size_t ilen);
  
  /**
   * \brief          This function finishes the SHA-256 operation, and writes
   *                 the result to the output buffer.
   *
   * \param ctx      The SHA-256 context. This must be initialized
   *                 and have a hash operation started.
   * \param output   The SHA-224 or SHA-256 checksum result.
   *                 This must be a writable buffer of length \c 32 bytes
   *                 for SHA-256, \c 28 bytes for SHA-224.
   *
   * \return         \c 0 on success.
   * \return         A negative error code on failure.
   */
  int mbedtls_sha256_finish_ret(mbedtls_sha256_context *ctx,
                                unsigned char *output);
  
  /**
   * \brief          This function processes a single data block within
   *                 the ongoing SHA-256 computation. This function is for
   *                 internal use only.
   *
   * \param ctx      The SHA-256 context. This must be initialized.
   * \param data     The buffer holding one block of data. This must
   *                 be a readable buffer of length \c 64 Bytes.
   *
   * \return         \c 0 on success.
   * \return         A negative error code on failure.
   */
  int mbedtls_internal_sha256_process(mbedtls_sha256_context *ctx,
                                      const unsigned char data[64]);
  
  /**
   * \brief          This function calculates the SHA-224 or SHA-256
   *                 checksum of a buffer.
   *
   *                 The function allocates the context, performs the
   *                 calculation, and frees the context.
   *
   *                 The SHA-256 result is calculated as
   *                 output = SHA-256(input buffer).
   *
   * \param input    The buffer holding the data. This must be a readable
   *                 buffer of length \p ilen Bytes.
   * \param ilen     The length of the input data in Bytes.
   * \param output   The SHA-224 or SHA-256 checksum result.
   *                 This must be a writable buffer of length \c 32 bytes
   *                 for SHA-256, \c 28 bytes for SHA-224.
   * \param is224    Determines which function to use. This must be
   *                 either \c 0 for SHA-256, or \c 1 for SHA-224.
   */
  int mbedtls_sha256_ret(const unsigned char *input,
                         size_t ilen,
                         unsigned char *output,
                         int is224);
  
  #if defined(MBEDTLS_SELF_TEST)
  
  /**
   * \brief          The SHA-224 and SHA-256 checkup routine.
   *
   * \return         \c 0 on success.
   * \return         \c 1 on failure.
   */
  int mbedtls_sha256_self_test(int verbose);
  
  #endif /* MBEDTLS_SELF_TEST */
  
  #ifdef __cplusplus
  }
  #endif
  
  #endif /* mbedtls_sha256.h */
  