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sha256.c

/* Functions to compute SHA256 message digest of files or memory blocks.
   according to the definition of SHA256 in FIPS 180-2.
   Copyright (C) 2007 Free Software Foundation, Inc.

   Copied here from the GNU C Library version 2.7 on the 10 May 2009
   by Steve McIntyre <93sam@debian.org>. This code was under LGPL v2.1
   in glibc, and that license gives us the option to use and
   distribute the code under the terms of the GPL v2 instead. I'm
   taking that option.

   This program is free software; you can redistribute it and/or modify it
   under the terms of the GNU General Public License as published by the
   Free Software Foundation; either version 2, or (at your option) any
   later version.

   This program 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 General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program; if not, write to the Free Software Foundation,
   Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.  */

/* Written by Ulrich Drepper <drepper@redhat.com>, 2007.  */

#ifdef HAVE_CONFIG_H
#include "config.h"
#endif

#include <stdlib.h>
#include <string.h>
#include <sys/types.h>

#include "sha256.h"

#if __BYTE_ORDER == __LITTLE_ENDIAN
# ifdef _LIBC
#  include <byteswap.h>
#  define SWAP(n) bswap_32 (n)
# else
#  define SWAP(n) \
    (((n) << 24) | (((n) & 0xff00) << 8) | (((n) >> 8) & 0xff00) | ((n) >> 24))
# endif
#else
# define SWAP(n) (n)
#endif


/* This array contains the bytes used to pad the buffer to the next
   64-byte boundary.  (FIPS 180-2:5.1.1)  */
static const unsigned char fillbuf[64] = { 0x80, 0 /* , 0, 0, ...  */ };


/* Constants for SHA256 from FIPS 180-2:4.2.2.  */
static const uint32_t K[64] =
  {
    0x428a2f98, 0x71374491, 0xb5c0fbcf, 0xe9b5dba5,
    0x3956c25b, 0x59f111f1, 0x923f82a4, 0xab1c5ed5,
    0xd807aa98, 0x12835b01, 0x243185be, 0x550c7dc3,
    0x72be5d74, 0x80deb1fe, 0x9bdc06a7, 0xc19bf174,
    0xe49b69c1, 0xefbe4786, 0x0fc19dc6, 0x240ca1cc,
    0x2de92c6f, 0x4a7484aa, 0x5cb0a9dc, 0x76f988da,
    0x983e5152, 0xa831c66d, 0xb00327c8, 0xbf597fc7,
    0xc6e00bf3, 0xd5a79147, 0x06ca6351, 0x14292967,
    0x27b70a85, 0x2e1b2138, 0x4d2c6dfc, 0x53380d13,
    0x650a7354, 0x766a0abb, 0x81c2c92e, 0x92722c85,
    0xa2bfe8a1, 0xa81a664b, 0xc24b8b70, 0xc76c51a3,
    0xd192e819, 0xd6990624, 0xf40e3585, 0x106aa070,
    0x19a4c116, 0x1e376c08, 0x2748774c, 0x34b0bcb5,
    0x391c0cb3, 0x4ed8aa4a, 0x5b9cca4f, 0x682e6ff3,
    0x748f82ee, 0x78a5636f, 0x84c87814, 0x8cc70208,
    0x90befffa, 0xa4506ceb, 0xbef9a3f7, 0xc67178f2
  };


/* Process LEN bytes of BUFFER, accumulating context into CTX.
   It is assumed that LEN % 64 == 0.  */
static void
sha256_process_block (const void *buffer, size_t len, struct sha256_ctx *ctx)
{
  const uint32_t *words = buffer;
  size_t nwords = len / sizeof (uint32_t);
  uint32_t a = ctx->H[0];
  uint32_t b = ctx->H[1];
  uint32_t c = ctx->H[2];
  uint32_t d = ctx->H[3];
  uint32_t e = ctx->H[4];
  uint32_t f = ctx->H[5];
  uint32_t g = ctx->H[6];
  uint32_t h = ctx->H[7];

  /* First increment the byte count.  FIPS 180-2 specifies the possible
     length of the file up to 2^64 bits.  Here we only compute the
     number of bytes.  Do a double word increment.  */
  ctx->total[0] += len;
  if (ctx->total[0] < len)
    ++ctx->total[1];

  /* Process all bytes in the buffer with 64 bytes in each round of
     the loop.  */
  while (nwords > 0)
    {
      uint32_t W[64];
      uint32_t a_save = a;
      uint32_t b_save = b;
      uint32_t c_save = c;
      uint32_t d_save = d;
      uint32_t e_save = e;
      uint32_t f_save = f;
      uint32_t g_save = g;
      uint32_t h_save = h;

      unsigned int t;

      /* Operators defined in FIPS 180-2:4.1.2.  */
#define Ch(x, y, z) ((x & y) ^ (~x & z))
#define Maj(x, y, z) ((x & y) ^ (x & z) ^ (y & z))
#define S0(x) (CYCLIC (x, 2) ^ CYCLIC (x, 13) ^ CYCLIC (x, 22))
#define S1(x) (CYCLIC (x, 6) ^ CYCLIC (x, 11) ^ CYCLIC (x, 25))
#define R0(x) (CYCLIC (x, 7) ^ CYCLIC (x, 18) ^ (x >> 3))
#define R1(x) (CYCLIC (x, 17) ^ CYCLIC (x, 19) ^ (x >> 10))

      /* It is unfortunate that C does not provide an operator for
       cyclic rotation.  Hope the C compiler is smart enough.  */
#define CYCLIC(w, s) ((w >> s) | (w << (32 - s)))

      /* Compute the message schedule according to FIPS 180-2:6.2.2 step 2.  */
      for (t = 0; t < 16; ++t)
      {
        W[t] = SWAP (*words);
        ++words;
      }
      for (t = 16; t < 64; ++t)
      W[t] = R1 (W[t - 2]) + W[t - 7] + R0 (W[t - 15]) + W[t - 16];

      /* The actual computation according to FIPS 180-2:6.2.2 step 3.  */
      for (t = 0; t < 64; ++t)
      {
        uint32_t T1 = h + S1 (e) + Ch (e, f, g) + K[t] + W[t];
        uint32_t T2 = S0 (a) + Maj (a, b, c);
        h = g;
        g = f;
        f = e;
        e = d + T1;
        d = c;
        c = b;
        b = a;
        a = T1 + T2;
      }

      /* Add the starting values of the context according to FIPS 180-2:6.2.2
       step 4.  */
      a += a_save;
      b += b_save;
      c += c_save;
      d += d_save;
      e += e_save;
      f += f_save;
      g += g_save;
      h += h_save;

      /* Prepare for the next round.  */
      nwords -= 16;
    }

  /* Put checksum in context given as argument.  */
  ctx->H[0] = a;
  ctx->H[1] = b;
  ctx->H[2] = c;
  ctx->H[3] = d;
  ctx->H[4] = e;
  ctx->H[5] = f;
  ctx->H[6] = g;
  ctx->H[7] = h;
}


/* Initialize structure containing state of computation.
   (FIPS 180-2:5.3.2)  */
void
sha256_init_ctx (ctx)
     struct sha256_ctx *ctx;
{
  ctx->H[0] = 0x6a09e667;
  ctx->H[1] = 0xbb67ae85;
  ctx->H[2] = 0x3c6ef372;
  ctx->H[3] = 0xa54ff53a;
  ctx->H[4] = 0x510e527f;
  ctx->H[5] = 0x9b05688c;
  ctx->H[6] = 0x1f83d9ab;
  ctx->H[7] = 0x5be0cd19;

  ctx->total[0] = ctx->total[1] = 0;
  ctx->buflen = 0;
}


/* Process the remaining bytes in the internal buffer and the usual
   prolog according to the standard and write the result to RESBUF.

   IMPORTANT: On some systems it is required that RESBUF is correctly
   aligned for a 32 bits value.  */
void *
sha256_finish_ctx (ctx, resbuf)
     struct sha256_ctx *ctx;
     void *resbuf;
{
  /* Take yet unprocessed bytes into account.  */
  uint32_t bytes = ctx->buflen;
  size_t pad;
  unsigned int i;

  /* Now count remaining bytes.  */
  ctx->total[0] += bytes;
  if (ctx->total[0] < bytes)
    ++ctx->total[1];

  pad = bytes >= 56 ? 64 + 56 - bytes : 56 - bytes;
  memcpy (&ctx->buffer[bytes], fillbuf, pad);

  /* Put the 64-bit file length in *bits* at the end of the buffer.  */
  *(uint32_t *) &ctx->buffer[bytes + pad + 4] = SWAP (ctx->total[0] << 3);
  *(uint32_t *) &ctx->buffer[bytes + pad] = SWAP ((ctx->total[1] << 3) |
                                      (ctx->total[0] >> 29));

  /* Process last bytes.  */
  sha256_process_block (ctx->buffer, bytes + pad + 8, ctx);

  /* Put result from CTX in first 32 bytes following RESBUF.  */
  for (i = 0; i < 8; ++i)
    ((uint32_t *) resbuf)[i] = SWAP (ctx->H[i]);

  return resbuf;
}


void
sha256_process_bytes (buffer, len, ctx)
     const void *buffer;
     size_t len;
     struct sha256_ctx *ctx;
{
  /* When we already have some bits in our internal buffer concatenate
     both inputs first.  */
  if (ctx->buflen != 0)
    {
      size_t left_over = ctx->buflen;
      size_t add = 128 - left_over > len ? len : 128 - left_over;

      memcpy (&ctx->buffer[left_over], buffer, add);
      ctx->buflen += add;

      if (ctx->buflen > 64)
      {
        sha256_process_block (ctx->buffer, ctx->buflen & ~63, ctx);

        ctx->buflen &= 63;
        /* The regions in the following copy operation cannot overlap.  */
        memcpy (ctx->buffer, &ctx->buffer[(left_over + add) & ~63],
              ctx->buflen);
      }

      buffer = (const char *) buffer + add;
      len -= add;
    }

  /* Process available complete blocks.  */
  if (len >= 64)
    {
#if !_STRING_ARCH_unaligned
/* To check alignment gcc has an appropriate operator.  Other
   compilers don't.  */
# if __GNUC__ >= 2
#  define UNALIGNED_P(p) (((uintptr_t) p) % __alignof__ (uint32_t) != 0)
# else
#  define UNALIGNED_P(p) (((uintptr_t) p) % sizeof (uint32_t) != 0)
# endif
      if (UNALIGNED_P (buffer))
      while (len > 64)
        {
          sha256_process_block (memcpy (ctx->buffer, buffer, 64), 64, ctx);
          buffer = (const char *) buffer + 64;
          len -= 64;
        }
      else
#endif
      {
        sha256_process_block (buffer, len & ~63, ctx);
        buffer = (const char *) buffer + (len & ~63);
        len &= 63;
      }
    }

  /* Move remaining bytes into internal buffer.  */
  if (len > 0)
    {
      size_t left_over = ctx->buflen;

      memcpy (&ctx->buffer[left_over], buffer, len);
      left_over += len;
      if (left_over >= 64)
      {
        sha256_process_block (ctx->buffer, 64, ctx);
        left_over -= 64;
        memcpy (ctx->buffer, &ctx->buffer[64], left_over);
      }
      ctx->buflen = left_over;
    }
}

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