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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.
   This file is part of the GNU C Library.

   The GNU C Library 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.

   The GNU C 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 the GNU C Library; if not, write to the Free
   Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
   02111-1307 USA.  */

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

#ifdef HAVE_CONFIG_H
# include <config.h>
#endif

#include <endian.h>
#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;

      /* 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 (unsigned int t = 0; t < 16; ++t)
      {
        W[t] = SWAP (*words);
        ++words;
      }
      for (unsigned int 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 (unsigned int 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;

  /* 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 (unsigned int 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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