githubmirror/libmicrohttpd

src/microhttpd/sha256.c
447 строк18 KB
Evgeny Grin (Karlson2k)
sha*/md5: fixed implicit value conversion
05 сен 2021, 17:39
05 сен 2021, 17:392646f3a
/*
     This file is part of libmicrohttpd
     Copyright (C) 2019-2021 Karlson2k (Evgeny Grin)

     libmicrohttpd is free software; you can redistribute it and/or
     modify it under the terms of the GNU Lesser General Public
     License as published by the Free Software Foundation; either
     version 2.1 of the License, or (at your option) any later version.

     This library is distributed in the hope that it will be useful,
     but WITHOUT ANY WARRANTY; without even the implied warranty of
     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
     Lesser General Public License for more details.

     You should have received a copy of the GNU Lesser General Public
     License along with this library.
     If not, see <http://www.gnu.org/licenses/>.
*/

/**
 * @file microhttpd/sha256.c
 * @brief  Calculation of SHA-256 digest as defined in FIPS PUB 180-4 (2015)
 * @author Karlson2k (Evgeny Grin)
 */

#include "sha256.h"

#include <string.h>
#ifdef HAVE_MEMORY_H
#include <memory.h>
#endif /* HAVE_MEMORY_H */
#include "mhd_bithelpers.h"
#include "mhd_assert.h"

/**
 * Initialise structure for SHA256 calculation.
 *
 * @param ctx_ must be a `struct sha256_ctx *`
 */
void
MHD_SHA256_init (void *ctx_)
{
  struct sha256_ctx *const ctx = ctx_;
  /* Initial hash values, see FIPS PUB 180-4 paragraph 5.3.3 */
  /* First thirty-two bits of the fractional parts of the square
   * roots of the first eight prime numbers: 2, 3, 5, 7, 11, 13,
   * 17, 19." */
  ctx->H[0] = UINT32_C (0x6a09e667);
  ctx->H[1] = UINT32_C (0xbb67ae85);
  ctx->H[2] = UINT32_C (0x3c6ef372);
  ctx->H[3] = UINT32_C (0xa54ff53a);
  ctx->H[4] = UINT32_C (0x510e527f);
  ctx->H[5] = UINT32_C (0x9b05688c);
  ctx->H[6] = UINT32_C (0x1f83d9ab);
  ctx->H[7] = UINT32_C (0x5be0cd19);

  /* Initialise number of bytes. */
  ctx->count = 0;
}


/**
 * Base of SHA-256 transformation.
 * Gets full 64 bytes block of data and updates hash values;
 * @param H     hash values
 * @param data  data, must be exactly 64 bytes long
 */
static void
sha256_transform (uint32_t H[_SHA256_DIGEST_LENGTH],
                  const uint8_t data[SHA256_BLOCK_SIZE])
{
  /* Working variables,
     see FIPS PUB 180-4 paragraph 6.2. */
  uint32_t a = H[0];
  uint32_t b = H[1];
  uint32_t c = H[2];
  uint32_t d = H[3];
  uint32_t e = H[4];
  uint32_t f = H[5];
  uint32_t g = H[6];
  uint32_t h = H[7];

  /* Data buffer, used as cyclic buffer.
     See FIPS PUB 180-4 paragraphs 5.2.1, 6.2. */
  uint32_t W[16];

  /* 'Ch' and 'Maj' macro functions are defined with
     widely-used optimization.
     See FIPS PUB 180-4 formulae 4.2, 4.3. */
#define Ch(x,y,z)     ( (z) ^ ((x) & ((y) ^ (z))) )
#define Maj(x,y,z)    ( ((x) & (y)) ^ ((z) & ((x) ^ (y))) )
  /* Unoptimized (original) versions: */
/* #define Ch(x,y,z)  ( ( (x) & (y) ) ^ ( ~(x) & (z) ) )          */
/* #define Maj(x,y,z) ( ((x) & (y)) ^ ((x) & (z)) ^ ((y) & (z)) ) */

  /* Four 'Sigma' macro functions.
     See FIPS PUB 180-4 formulae 4.4, 4.5, 4.6, 4.7. */
#define SIG0(x)  (_MHD_ROTR32 ((x), 2) ^ _MHD_ROTR32 ((x), 13) ^ \
                  _MHD_ROTR32 ((x), 22) )
#define SIG1(x)  (_MHD_ROTR32 ((x), 6) ^ _MHD_ROTR32 ((x), 11) ^ \
                  _MHD_ROTR32 ((x), 25) )
#define sig0(x)  (_MHD_ROTR32 ((x), 7) ^ _MHD_ROTR32 ((x), 18) ^ \
                  ((x) >> 3) )
#define sig1(x)  (_MHD_ROTR32 ((x), 17) ^ _MHD_ROTR32 ((x),19) ^ \
                  ((x) >> 10) )

  /* Single step of SHA-256 computation,
     see FIPS PUB 180-4 paragraph 6.2.2 step 3.
   * Note: instead of reassigning all working variables on each step,
           variables are rotated for each step:
             SHA2STEP32(a, b, c, d, e, f, g, h, K[0], data[0]);
             SHA2STEP32(h, a, b, c, d, e, f, g, K[1], data[1]);
           so current 'vD' will be used as 'vE' on next step,
           current 'vH' will be used as 'vA' on next step.
   * Note: first (vH += SIG1(vE) + Ch(vE,vF,vG) + kt + wt) equals T1 in FIPS PUB 180-4 paragraph 6.2.2 step 3.
           second (vH += SIG0(vA) + Maj(vE,vF,vC) equals T1 + T2 in FIPS PUB 180-4 paragraph 6.2.2 step 3.
   * Note: 'wt' must be used exactly one time in this macro as it change other data as well
           every time when used. */
#define SHA2STEP32(vA,vB,vC,vD,vE,vF,vG,vH,kt,wt) do {                  \
    (vD) += ((vH) += SIG1 ((vE)) + Ch ((vE),(vF),(vG)) + (kt) + (wt));  \
    (vH) += SIG0 ((vA)) + Maj ((vA),(vB),(vC)); } while (0)

#ifndef _MHD_GET_32BIT_BE_UNALIGNED
  if (0 != (((uintptr_t) data) % _MHD_UINT32_ALIGN))
  {
    /* Copy the unaligned input data to the aligned buffer */
    memcpy (W, data, SHA256_BLOCK_SIZE);
    /* The W[] buffer itself will be used as the source of the data,
     * but data will be reloaded in correct bytes order during
     * the next steps */
    data = (uint8_t*) W;
  }
#endif /* _MHD_GET_32BIT_BE_UNALIGNED */

  /* Get value of W(t) from input data buffer,
     See FIPS PUB 180-4 paragraph 6.2.
     Input data must be read in big-endian bytes order,
     see FIPS PUB 180-4 paragraph 3.1.2. */
#define GET_W_FROM_DATA(buf,t) \
  _MHD_GET_32BIT_BE (((const uint8_t*) (buf)) + (t) * SHA256_BYTES_IN_WORD)

  /* During first 16 steps, before making any calculations on each step,
     the W element is read from input data buffer as big-endian value and
     stored in array of W elements. */
  /* Note: instead of using K constants as array, all K values are specified
     individually for each step, see FIPS PUB 180-4 paragraph 4.2.2 for K values. */
  SHA2STEP32 (a, b, c, d, e, f, g, h, UINT32_C (0x428a2f98), W[0] = \
                GET_W_FROM_DATA (data, 0));
  SHA2STEP32 (h, a, b, c, d, e, f, g, UINT32_C (0x71374491), W[1] = \
                GET_W_FROM_DATA (data, 1));
  SHA2STEP32 (g, h, a, b, c, d, e, f, UINT32_C (0xb5c0fbcf), W[2] = \
                GET_W_FROM_DATA (data, 2));
  SHA2STEP32 (f, g, h, a, b, c, d, e, UINT32_C (0xe9b5dba5), W[3] = \
                GET_W_FROM_DATA (data, 3));
  SHA2STEP32 (e, f, g, h, a, b, c, d, UINT32_C (0x3956c25b), W[4] = \
                GET_W_FROM_DATA (data, 4));
  SHA2STEP32 (d, e, f, g, h, a, b, c, UINT32_C (0x59f111f1), W[5] = \
                GET_W_FROM_DATA (data, 5));
  SHA2STEP32 (c, d, e, f, g, h, a, b, UINT32_C (0x923f82a4), W[6] = \
                GET_W_FROM_DATA (data, 6));
  SHA2STEP32 (b, c, d, e, f, g, h, a, UINT32_C (0xab1c5ed5), W[7] = \
                GET_W_FROM_DATA (data, 7));
  SHA2STEP32 (a, b, c, d, e, f, g, h, UINT32_C (0xd807aa98), W[8] = \
                GET_W_FROM_DATA (data, 8));
  SHA2STEP32 (h, a, b, c, d, e, f, g, UINT32_C (0x12835b01), W[9] = \
                GET_W_FROM_DATA (data, 9));
  SHA2STEP32 (g, h, a, b, c, d, e, f, UINT32_C (0x243185be), W[10] = \
                GET_W_FROM_DATA (data, 10));
  SHA2STEP32 (f, g, h, a, b, c, d, e, UINT32_C (0x550c7dc3), W[11] = \
                GET_W_FROM_DATA (data, 11));
  SHA2STEP32 (e, f, g, h, a, b, c, d, UINT32_C (0x72be5d74), W[12] = \
                GET_W_FROM_DATA (data, 12));
  SHA2STEP32 (d, e, f, g, h, a, b, c, UINT32_C (0x80deb1fe), W[13] = \
                GET_W_FROM_DATA (data, 13));
  SHA2STEP32 (c, d, e, f, g, h, a, b, UINT32_C (0x9bdc06a7), W[14] = \
                GET_W_FROM_DATA (data, 14));
  SHA2STEP32 (b, c, d, e, f, g, h, a, UINT32_C (0xc19bf174), W[15] = \
                GET_W_FROM_DATA (data, 15));

  /* 'W' generation and assignment for 16 <= t <= 63.
     See FIPS PUB 180-4 paragraph 6.2.2.
     As only last 16 'W' are used in calculations, it is possible to
     use 16 elements array of W as cyclic buffer.
   * Note: ((t-16)&0xf) have same value as (t&0xf) */
#define Wgen(w,t) ( (w)[(t - 16) & 0xf] + sig1 ((w)[((t) - 2) & 0xf])   \
                    + (w)[((t) - 7) & 0xf] + sig0 ((w)[((t) - 15) & 0xf]) )

  /* During last 48 steps, before making any calculations on each step,
     W element is generated from W elements of cyclic buffer and generated value
     stored back in cyclic buffer. */
  /* Note: instead of using K constants as array, all K values are specified
     individually for each step, see FIPS PUB 180-4 paragraph 4.2.2 for K values. */
  SHA2STEP32 (a, b, c, d, e, f, g, h, UINT32_C (0xe49b69c1), W[16 & 0xf] = \
                Wgen (W,16));
  SHA2STEP32 (h, a, b, c, d, e, f, g, UINT32_C (0xefbe4786), W[17 & 0xf] = \
                Wgen (W,17));
  SHA2STEP32 (g, h, a, b, c, d, e, f, UINT32_C (0x0fc19dc6), W[18 & 0xf] = \
                Wgen (W,18));
  SHA2STEP32 (f, g, h, a, b, c, d, e, UINT32_C (0x240ca1cc), W[19 & 0xf] = \
                Wgen (W,19));
  SHA2STEP32 (e, f, g, h, a, b, c, d, UINT32_C (0x2de92c6f), W[20 & 0xf] = \
                Wgen (W,20));
  SHA2STEP32 (d, e, f, g, h, a, b, c, UINT32_C (0x4a7484aa), W[21 & 0xf] = \
                Wgen (W,21));
  SHA2STEP32 (c, d, e, f, g, h, a, b, UINT32_C (0x5cb0a9dc), W[22 & 0xf] = \
                Wgen (W,22));
  SHA2STEP32 (b, c, d, e, f, g, h, a, UINT32_C (0x76f988da), W[23 & 0xf] = \
                Wgen (W,23));
  SHA2STEP32 (a, b, c, d, e, f, g, h, UINT32_C (0x983e5152), W[24 & 0xf] = \
                Wgen (W,24));
  SHA2STEP32 (h, a, b, c, d, e, f, g, UINT32_C (0xa831c66d), W[25 & 0xf] = \
                Wgen (W,25));
  SHA2STEP32 (g, h, a, b, c, d, e, f, UINT32_C (0xb00327c8), W[26 & 0xf] = \
                Wgen (W,26));
  SHA2STEP32 (f, g, h, a, b, c, d, e, UINT32_C (0xbf597fc7), W[27 & 0xf] = \
                Wgen (W,27));
  SHA2STEP32 (e, f, g, h, a, b, c, d, UINT32_C (0xc6e00bf3), W[28 & 0xf] = \
                Wgen (W,28));
  SHA2STEP32 (d, e, f, g, h, a, b, c, UINT32_C (0xd5a79147), W[29 & 0xf] = \
                Wgen (W,29));
  SHA2STEP32 (c, d, e, f, g, h, a, b, UINT32_C (0x06ca6351), W[30 & 0xf] = \
                Wgen (W,30));
  SHA2STEP32 (b, c, d, e, f, g, h, a, UINT32_C (0x14292967), W[31 & 0xf] = \
                Wgen (W,31));
  SHA2STEP32 (a, b, c, d, e, f, g, h, UINT32_C (0x27b70a85), W[32 & 0xf] = \
                Wgen (W,32));
  SHA2STEP32 (h, a, b, c, d, e, f, g, UINT32_C (0x2e1b2138), W[33 & 0xf] = \
                Wgen (W,33));
  SHA2STEP32 (g, h, a, b, c, d, e, f, UINT32_C (0x4d2c6dfc), W[34 & 0xf] = \
                Wgen (W,34));
  SHA2STEP32 (f, g, h, a, b, c, d, e, UINT32_C (0x53380d13), W[35 & 0xf] = \
                Wgen (W,35));
  SHA2STEP32 (e, f, g, h, a, b, c, d, UINT32_C (0x650a7354), W[36 & 0xf] = \
                Wgen (W,36));
  SHA2STEP32 (d, e, f, g, h, a, b, c, UINT32_C (0x766a0abb), W[37 & 0xf] = \
                Wgen (W,37));
  SHA2STEP32 (c, d, e, f, g, h, a, b, UINT32_C (0x81c2c92e), W[38 & 0xf] = \
                Wgen (W,38));
  SHA2STEP32 (b, c, d, e, f, g, h, a, UINT32_C (0x92722c85), W[39 & 0xf] = \
                Wgen (W,39));
  SHA2STEP32 (a, b, c, d, e, f, g, h, UINT32_C (0xa2bfe8a1), W[40 & 0xf] = \
                Wgen (W,40));
  SHA2STEP32 (h, a, b, c, d, e, f, g, UINT32_C (0xa81a664b), W[41 & 0xf] = \
                Wgen (W,41));
  SHA2STEP32 (g, h, a, b, c, d, e, f, UINT32_C (0xc24b8b70), W[42 & 0xf] = \
                Wgen (W,42));
  SHA2STEP32 (f, g, h, a, b, c, d, e, UINT32_C (0xc76c51a3), W[43 & 0xf] = \
                Wgen (W,43));
  SHA2STEP32 (e, f, g, h, a, b, c, d, UINT32_C (0xd192e819), W[44 & 0xf] = \
                Wgen (W,44));
  SHA2STEP32 (d, e, f, g, h, a, b, c, UINT32_C (0xd6990624), W[45 & 0xf] = \
                Wgen (W,45));
  SHA2STEP32 (c, d, e, f, g, h, a, b, UINT32_C (0xf40e3585), W[46 & 0xf] = \
                Wgen (W,46));
  SHA2STEP32 (b, c, d, e, f, g, h, a, UINT32_C (0x106aa070), W[47 & 0xf] = \
                Wgen (W,47));
  SHA2STEP32 (a, b, c, d, e, f, g, h, UINT32_C (0x19a4c116), W[48 & 0xf] = \
                Wgen (W,48));
  SHA2STEP32 (h, a, b, c, d, e, f, g, UINT32_C (0x1e376c08), W[49 & 0xf] = \
                Wgen (W,49));
  SHA2STEP32 (g, h, a, b, c, d, e, f, UINT32_C (0x2748774c), W[50 & 0xf] = \
                Wgen (W,50));
  SHA2STEP32 (f, g, h, a, b, c, d, e, UINT32_C (0x34b0bcb5), W[51 & 0xf] = \
                Wgen (W,51));
  SHA2STEP32 (e, f, g, h, a, b, c, d, UINT32_C (0x391c0cb3), W[52 & 0xf] = \
                Wgen (W,52));
  SHA2STEP32 (d, e, f, g, h, a, b, c, UINT32_C (0x4ed8aa4a), W[53 & 0xf] = \
                Wgen (W,53));
  SHA2STEP32 (c, d, e, f, g, h, a, b, UINT32_C (0x5b9cca4f), W[54 & 0xf] = \
                Wgen (W,54));
  SHA2STEP32 (b, c, d, e, f, g, h, a, UINT32_C (0x682e6ff3), W[55 & 0xf] = \
                Wgen (W,55));
  SHA2STEP32 (a, b, c, d, e, f, g, h, UINT32_C (0x748f82ee), W[56 & 0xf] = \
                Wgen (W,56));
  SHA2STEP32 (h, a, b, c, d, e, f, g, UINT32_C (0x78a5636f), W[57 & 0xf] = \
                Wgen (W,57));
  SHA2STEP32 (g, h, a, b, c, d, e, f, UINT32_C (0x84c87814), W[58 & 0xf] = \
                Wgen (W,58));
  SHA2STEP32 (f, g, h, a, b, c, d, e, UINT32_C (0x8cc70208), W[59 & 0xf] = \
                Wgen (W,59));
  SHA2STEP32 (e, f, g, h, a, b, c, d, UINT32_C (0x90befffa), W[60 & 0xf] = \
                Wgen (W,60));
  SHA2STEP32 (d, e, f, g, h, a, b, c, UINT32_C (0xa4506ceb), W[61 & 0xf] = \
                Wgen (W,61));
  SHA2STEP32 (c, d, e, f, g, h, a, b, UINT32_C (0xbef9a3f7), W[62 & 0xf] = \
                Wgen (W,62));
  SHA2STEP32 (b, c, d, e, f, g, h, a, UINT32_C (0xc67178f2), W[63 & 0xf] = \
                Wgen (W,63));

  /* Compute intermediate hash.
     See FIPS PUB 180-4 paragraph 6.2.2 step 4. */
  H[0] += a;
  H[1] += b;
  H[2] += c;
  H[3] += d;
  H[4] += e;
  H[5] += f;
  H[6] += g;
  H[7] += h;
}


/**
 * Process portion of bytes.
 *
 * @param ctx_ must be a `struct sha256_ctx *`
 * @param data bytes to add to hash
 * @param length number of bytes in @a data
 */
void
MHD_SHA256_update (void *ctx_,
                   const uint8_t *data,
                   size_t length)
{
  struct sha256_ctx *const ctx = ctx_;
  unsigned bytes_have; /**< Number of bytes in buffer */

  mhd_assert ((data != NULL) || (length == 0));

  if (0 == length)
    return; /* Do nothing */

  /* Note: (count & (SHA256_BLOCK_SIZE-1))
           equals (count % SHA256_BLOCK_SIZE) for this block size. */
  bytes_have = (unsigned) (ctx->count & (SHA256_BLOCK_SIZE - 1));
  ctx->count += length;

  if (0 != bytes_have)
  {
    unsigned bytes_left = SHA256_BLOCK_SIZE - bytes_have;
    if (length >= bytes_left)
    {     /* Combine new data with data in the buffer and
             process full block. */
      memcpy (ctx->buffer + bytes_have,
              data,
              bytes_left);
      data += bytes_left;
      length -= bytes_left;
      sha256_transform (ctx->H, ctx->buffer);
      bytes_have = 0;
    }
  }

  while (SHA256_BLOCK_SIZE <= length)
  {   /* Process any full blocks of new data directly,
         without copying to the buffer. */
    sha256_transform (ctx->H, data);
    data += SHA256_BLOCK_SIZE;
    length -= SHA256_BLOCK_SIZE;
  }

  if (0 != length)
  {   /* Copy incomplete block of new data (if any)
         to the buffer. */
    memcpy (ctx->buffer + bytes_have, data, length);
  }
}


/**
 * Size of "length" padding addition in bytes.
 * See FIPS PUB 180-4 paragraph 5.1.1.
 */
#define SHA256_SIZE_OF_LEN_ADD (64 / 8)

/**
 * Finalise SHA256 calculation, return digest.
 *
 * @param ctx_ must be a `struct sha256_ctx *`
 * @param[out] digest set to the hash, must be #SHA256_DIGEST_SIZE bytes
 */
void
MHD_SHA256_finish (void *ctx_,
                   uint8_t digest[SHA256_DIGEST_SIZE])
{
  struct sha256_ctx *const ctx = ctx_;
  uint64_t num_bits;   /**< Number of processed bits */
  unsigned bytes_have; /**< Number of bytes in buffer */

  num_bits = ctx->count << 3;
  /* Note: (count & (SHA256_BLOCK_SIZE-1))
           equal (count % SHA256_BLOCK_SIZE) for this block size. */
  bytes_have = (unsigned) (ctx->count & (SHA256_BLOCK_SIZE - 1));

  /* Input data must be padded with bit "1" and with length of data in bits.
     See FIPS PUB 180-4 paragraph 5.1.1. */
  /* Data is always processed in form of bytes (not by individual bits),
     therefore position of first padding bit in byte is always predefined (0x80). */
  /* Buffer always have space at least for one byte (as full buffers are
     processed immediately). */
  ctx->buffer[bytes_have++] = 0x80;

  if (SHA256_BLOCK_SIZE - bytes_have < SHA256_SIZE_OF_LEN_ADD)
  {   /* No space in current block to put total length of message.
         Pad current block with zeros and process it. */
    if (bytes_have < SHA256_BLOCK_SIZE)
      memset (ctx->buffer + bytes_have, 0, SHA256_BLOCK_SIZE - bytes_have);
    /* Process full block. */
    sha256_transform (ctx->H, ctx->buffer);
    /* Start new block. */
    bytes_have = 0;
  }

  /* Pad the rest of the buffer with zeros. */
  memset (ctx->buffer + bytes_have, 0,
          SHA256_BLOCK_SIZE - SHA256_SIZE_OF_LEN_ADD - bytes_have);
  /* Put number of bits in processed message as big-endian value. */
  _MHD_PUT_64BIT_BE_SAFE (ctx->buffer + SHA256_BLOCK_SIZE
                          - SHA256_SIZE_OF_LEN_ADD,
                          num_bits);
  /* Process full final block. */
  sha256_transform (ctx->H, ctx->buffer);

  /* Put final hash/digest in BE mode */
#ifndef _MHD_PUT_32BIT_BE_UNALIGNED
  if (0 != ((uintptr_t) digest) % _MHD_UINT32_ALIGN)
  {
    uint32_t alig_dgst[_SHA256_DIGEST_LENGTH];
    _MHD_PUT_32BIT_BE (alig_dgst + 0, ctx->H[0]);
    _MHD_PUT_32BIT_BE (alig_dgst + 1, ctx->H[1]);
    _MHD_PUT_32BIT_BE (alig_dgst + 2, ctx->H[2]);
    _MHD_PUT_32BIT_BE (alig_dgst + 3, ctx->H[3]);
    _MHD_PUT_32BIT_BE (alig_dgst + 4, ctx->H[4]);
    _MHD_PUT_32BIT_BE (alig_dgst + 5, ctx->H[5]);
    _MHD_PUT_32BIT_BE (alig_dgst + 6, ctx->H[6]);
    _MHD_PUT_32BIT_BE (alig_dgst + 7, ctx->H[7]);
    /* Copy result to unaligned destination address */
    memcpy (digest, alig_dgst, SHA256_DIGEST_SIZE);
  }
  else
#else  /* _MHD_PUT_32BIT_BE_UNALIGNED */
  if (1)
#endif /* _MHD_PUT_32BIT_BE_UNALIGNED */
  {
    _MHD_PUT_32BIT_BE (digest + 0 * SHA256_BYTES_IN_WORD, ctx->H[0]);
    _MHD_PUT_32BIT_BE (digest + 1 * SHA256_BYTES_IN_WORD, ctx->H[1]);
    _MHD_PUT_32BIT_BE (digest + 2 * SHA256_BYTES_IN_WORD, ctx->H[2]);
    _MHD_PUT_32BIT_BE (digest + 3 * SHA256_BYTES_IN_WORD, ctx->H[3]);
    _MHD_PUT_32BIT_BE (digest + 4 * SHA256_BYTES_IN_WORD, ctx->H[4]);
    _MHD_PUT_32BIT_BE (digest + 5 * SHA256_BYTES_IN_WORD, ctx->H[5]);
    _MHD_PUT_32BIT_BE (digest + 6 * SHA256_BYTES_IN_WORD, ctx->H[6]);
    _MHD_PUT_32BIT_BE (digest + 7 * SHA256_BYTES_IN_WORD, ctx->H[7]);
  }

  /* Erase potentially sensitive data. */
  memset (ctx, 0, sizeof(struct sha256_ctx));
}