/* sha256 implementation, taken (with minor modification) from sha256crypt.c,
   which states:
   Released into the Public Domain by Ulrich Drepper <drepper@redhat.com>.
   Neglegible modifications by Bernhard R. Link, also in the public domain.
*/

#include <config.h>

#include <limits.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/param.h>
#include <sys/types.h>

#include "sha256.h"

#ifndef WORDS_BIGENDIAN
# define SWAP(n) \
    (((n) << 24) | (((n) & 0xff00) << 8) | (((n) >> 8) & 0xff00) | ((n) >> 24))
#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_Context *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. */
  ctx->total += len;

  /* 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
SHA256Init(struct SHA256_Context *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->buflen = 0;
}


/* Process the remaining bytes in the internal buffer and the usual
   prolog according to the standard and write the result to digest.
   */
void
SHA256Final(struct SHA256_Context *ctx, uint8_t *digest)
{
  /* Take yet unprocessed bytes into account.  */
  uint32_t bytes = ctx->buflen;
  uint32_t bitslow, bitshigh;
  size_t pad;
  int i;

  /* Now count remaining bytes.  */
  ctx->total += bytes;

  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.  */
  bitslow = ctx->total << 3;
  bitshigh = ctx->total >> 29;
  bitslow = SWAP(bitslow);
  memcpy(ctx->buffer + bytes + pad + 4, &bitslow, 4);
  bitshigh = SWAP(bitshigh);
  memcpy(ctx->buffer + bytes + pad, &bitshigh, 4);

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

  for (i = 0; i < SHA256_DIGEST_SIZE; i++) {
        digest[i] = (uint8_t)
         ((ctx->H[i>>2] >> ((3-(i & 3)) * 8) ) & 255);
  }
}


void
SHA256Update(struct SHA256_Context *ctx, const uint8_t *buffer, size_t len)
{
  /* 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 = buffer + add;
      len -= add;
    }

  /* Process available complete blocks.  */
  if (len >= 64)
    {
/* 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 = buffer + 64;
	    len -= 64;
	  }
      else
	{
	  sha256_process_block (buffer, len & ~63, ctx);
	  buffer = 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;
    }
}
