SHA1.cpp

/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

#include "mozilla/Assertions.h"
#include "mozilla/SHA1.h"

#include <string.h>

// FIXME: We should probably create a more complete mfbt/Endian.h. This assumes
// that any compiler that doesn't define these macros is little endian.
#if defined(__BYTE_ORDER__) && defined(__ORDER_LITTLE_ENDIAN__)
#  if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
#    define MOZ_IS_LITTLE_ENDIAN
#  endif
#else
#  define MOZ_IS_LITTLE_ENDIAN
#endif

using mozilla::SHA1Sum;

static inline uint32_t
SHA_ROTL(uint32_t t, uint32_t n)
{
  MOZ_ASSERT(n < 32);
  return (t << n) | (t >> (32 - n));
}

static inline unsigned
SHA_HTONL(unsigned x)
{
#ifdef MOZ_IS_LITTLE_ENDIAN
  const unsigned int mask = 0x00FF00FF;
  x = (x << 16) | (x >> 16);
  return ((x & mask) << 8) | ((x >> 8) & mask);
#else
  return x;
#endif
}

static void
shaCompress(volatile unsigned* X, const uint32_t* datain);

#define SHA_F1(X, Y, Z) ((((Y) ^ (Z)) & (X)) ^ (Z))
#define SHA_F2(X, Y, Z) ((X) ^ (Y) ^ (Z))
#define SHA_F3(X, Y, Z) (((X) & (Y)) | ((Z) & ((X) | (Y))))
#define SHA_F4(X, Y, Z) ((X) ^ (Y) ^ (Z))

#define SHA_MIX(n, a, b, c)    XW(n) = SHA_ROTL(XW(a) ^ XW(b) ^ XW(c) ^XW(n), 1)

SHA1Sum::SHA1Sum()
  : size(0), mDone(false)
{
  // Initialize H with constants from FIPS180-1.
  H[0] = 0x67452301L;
  H[1] = 0xefcdab89L;
  H[2] = 0x98badcfeL;
  H[3] = 0x10325476L;
  H[4] = 0xc3d2e1f0L;
}

/*
 * Explanation of H array and index values:
 *
 * The context's H array is actually the concatenation of two arrays
 * defined by SHA1, the H array of state variables (5 elements),
 * and the W array of intermediate values, of which there are 16 elements.
 * The W array starts at H[5], that is W[0] is H[5].
 * Although these values are defined as 32-bit values, we use 64-bit
 * variables to hold them because the AMD64 stores 64 bit values in
 * memory MUCH faster than it stores any smaller values.
 *
 * Rather than passing the context structure to shaCompress, we pass
 * this combined array of H and W values.  We do not pass the address
 * of the first element of this array, but rather pass the address of an
 * element in the middle of the array, element X.  Presently X[0] is H[11].
 * So we pass the address of H[11] as the address of array X to shaCompress.
 * Then shaCompress accesses the members of the array using positive AND
 * negative indexes.
 *
 * Pictorially: (each element is 8 bytes)
 * H | H0 H1 H2 H3 H4 W0 W1 W2 W3 W4 W5 W6 W7 W8 W9 Wa Wb Wc Wd We Wf |
 * X |-11-10 -9 -8 -7 -6 -5 -4 -3 -2 -1 X0 X1 X2 X3 X4 X5 X6 X7 X8 X9 |
 *
 * The byte offset from X[0] to any member of H and W is always
 * representable in a signed 8-bit value, which will be encoded
 * as a single byte offset in the X86-64 instruction set.
 * If we didn't pass the address of H[11], and instead passed the
 * address of H[0], the offsets to elements H[16] and above would be
 * greater than 127, not representable in a signed 8-bit value, and the
 * x86-64 instruction set would encode every such offset as a 32-bit
 * signed number in each instruction that accessed element H[16] or
 * higher.  This results in much bigger and slower code.
 */
#define H2X 11 /* X[0] is H[11], and H[0] is X[-11] */
#define W2X  6 /* X[0] is W[6],  and W[0] is X[-6]  */

/*
 *  SHA: Add data to context.
 */
void
SHA1Sum::update(const void* dataIn, uint32_t len)
{
  MOZ_ASSERT(!mDone, "SHA1Sum can only be used to compute a single hash.");

  const uint8_t* data = static_cast<const uint8_t*>(dataIn);

  if (len == 0)
    return;

  /* Accumulate the byte count. */
  unsigned int lenB = static_cast<unsigned int>(size) & 63U;

  size += len;

  /* Read the data into W and process blocks as they get full. */
  unsigned int togo;
  if (lenB > 0) {
    togo = 64U - lenB;
    if (len < togo)
      togo = len;
    memcpy(u.b + lenB, data, togo);
    len -= togo;
    data += togo;
    lenB = (lenB + togo) & 63U;
    if (!lenB)
      shaCompress(&H[H2X], u.w);
  }

  while (len >= 64U) {
    len -= 64U;
    shaCompress(&H[H2X], reinterpret_cast<const uint32_t*>(data));
    data += 64U;
  }

  if (len > 0)
    memcpy(u.b, data, len);
}


/*
 *  SHA: Generate hash value
 */
void
SHA1Sum::finish(SHA1Sum::Hash& hashOut)
{
  MOZ_ASSERT(!mDone, "SHA1Sum can only be used to compute a single hash.");

  uint64_t size2 = size;
  uint32_t lenB = uint32_t(size2) & 63;

  static const uint8_t bulk_pad[64] =
    { 0x80,0,0,0,0,0,0,0,0,0,
      0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
      0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0 };

  /* Pad with a binary 1 (e.g. 0x80), then zeroes, then length in bits. */
  update(bulk_pad, (((55 + 64) - lenB) & 63) + 1);
  MOZ_ASSERT((uint32_t(size) & 63) == 56);

  /* Convert size from bytes to bits. */
  size2 <<= 3;
  u.w[14] = SHA_HTONL(uint32_t(size2 >> 32));
  u.w[15] = SHA_HTONL(uint32_t(size2));
  shaCompress(&H[H2X], u.w);

  /* Output hash. */
  u.w[0] = SHA_HTONL(H[0]);
  u.w[1] = SHA_HTONL(H[1]);
  u.w[2] = SHA_HTONL(H[2]);
  u.w[3] = SHA_HTONL(H[3]);
  u.w[4] = SHA_HTONL(H[4]);
  memcpy(hashOut, u.w, 20);
  mDone = true;
}

/*
 *  SHA: Compression function, unrolled.
 *
 * Some operations in shaCompress are done as 5 groups of 16 operations.
 * Others are done as 4 groups of 20 operations.
 * The code below shows that structure.
 *
 * The functions that compute the new values of the 5 state variables
 * A-E are done in 4 groups of 20 operations (or you may also think
 * of them as being done in 16 groups of 5 operations).  They are
 * done by the SHA_RNDx macros below, in the right column.
 *
 * The functions that set the 16 values of the W array are done in
 * 5 groups of 16 operations.  The first group is done by the
 * LOAD macros below, the latter 4 groups are done by SHA_MIX below,
 * in the left column.
 *
 * gcc's optimizer observes that each member of the W array is assigned
 * a value 5 times in this code.  It reduces the number of store
 * operations done to the W array in the context (that is, in the X array)
 * by creating a W array on the stack, and storing the W values there for
 * the first 4 groups of operations on W, and storing the values in the
 * context's W array only in the fifth group.  This is undesirable.
 * It is MUCH bigger code than simply using the context's W array, because
 * all the offsets to the W array in the stack are 32-bit signed offsets,
 * and it is no faster than storing the values in the context's W array.
 *
 * The original code for sha_fast.c prevented this creation of a separate
 * W array in the stack by creating a W array of 80 members, each of
 * whose elements is assigned only once. It also separated the computations
 * of the W array values and the computations of the values for the 5
 * state variables into two separate passes, W's, then A-E's so that the 
 * second pass could be done all in registers (except for accessing the W
 * array) on machines with fewer registers.  The method is suboptimal
 * for machines with enough registers to do it all in one pass, and it
 * necessitates using many instructions with 32-bit offsets.
 *
 * This code eliminates the separate W array on the stack by a completely
 * different means: by declaring the X array volatile.  This prevents
 * the optimizer from trying to reduce the use of the X array by the
 * creation of a MORE expensive W array on the stack. The result is
 * that all instructions use signed 8-bit offsets and not 32-bit offsets.
 *
 * The combination of this code and the -O3 optimizer flag on GCC 3.4.3
 * results in code that is 3 times faster than the previous NSS sha_fast
 * code on AMD64.
 */
static void
shaCompress(volatile unsigned *X, const uint32_t *inbuf)
{
  unsigned A, B, C, D, E;

#define XH(n) X[n - H2X]
#define XW(n) X[n - W2X]

#define K0 0x5a827999L
#define K1 0x6ed9eba1L
#define K2 0x8f1bbcdcL
#define K3 0xca62c1d6L

#define SHA_RND1(a, b, c, d, e, n) \
  a = SHA_ROTL(b, 5) + SHA_F1(c, d, e) + a + XW(n) + K0; c = SHA_ROTL(c, 30)
#define SHA_RND2(a, b, c, d, e, n) \
  a = SHA_ROTL(b, 5) + SHA_F2(c, d, e) + a + XW(n) + K1; c = SHA_ROTL(c, 30)
#define SHA_RND3(a, b, c, d, e, n) \
  a = SHA_ROTL(b, 5) + SHA_F3(c, d, e) + a + XW(n) + K2; c = SHA_ROTL(c, 30)
#define SHA_RND4(a, b, c, d, e, n) \
  a = SHA_ROTL(b ,5) + SHA_F4(c, d, e) + a + XW(n) + K3; c = SHA_ROTL(c, 30)

#define LOAD(n) XW(n) = SHA_HTONL(inbuf[n])

  A = XH(0);
  B = XH(1);
  C = XH(2);
  D = XH(3);
  E = XH(4);

  LOAD(0);		   SHA_RND1(E,A,B,C,D, 0);
  LOAD(1);		   SHA_RND1(D,E,A,B,C, 1);
  LOAD(2);		   SHA_RND1(C,D,E,A,B, 2);
  LOAD(3);		   SHA_RND1(B,C,D,E,A, 3);
  LOAD(4);		   SHA_RND1(A,B,C,D,E, 4);
  LOAD(5);		   SHA_RND1(E,A,B,C,D, 5);
  LOAD(6);		   SHA_RND1(D,E,A,B,C, 6);
  LOAD(7);		   SHA_RND1(C,D,E,A,B, 7);
  LOAD(8);		   SHA_RND1(B,C,D,E,A, 8);
  LOAD(9);		   SHA_RND1(A,B,C,D,E, 9);
  LOAD(10);		   SHA_RND1(E,A,B,C,D,10);
  LOAD(11);		   SHA_RND1(D,E,A,B,C,11);
  LOAD(12);		   SHA_RND1(C,D,E,A,B,12);
  LOAD(13);		   SHA_RND1(B,C,D,E,A,13);
  LOAD(14);		   SHA_RND1(A,B,C,D,E,14);
  LOAD(15);		   SHA_RND1(E,A,B,C,D,15);

  SHA_MIX( 0, 13,  8,  2); SHA_RND1(D,E,A,B,C, 0);
  SHA_MIX( 1, 14,  9,  3); SHA_RND1(C,D,E,A,B, 1);
  SHA_MIX( 2, 15, 10,  4); SHA_RND1(B,C,D,E,A, 2);
  SHA_MIX( 3,  0, 11,  5); SHA_RND1(A,B,C,D,E, 3);

  SHA_MIX( 4,  1, 12,  6); SHA_RND2(E,A,B,C,D, 4);
  SHA_MIX( 5,  2, 13,  7); SHA_RND2(D,E,A,B,C, 5);
  SHA_MIX( 6,  3, 14,  8); SHA_RND2(C,D,E,A,B, 6);
  SHA_MIX( 7,  4, 15,  9); SHA_RND2(B,C,D,E,A, 7);
  SHA_MIX( 8,  5,  0, 10); SHA_RND2(A,B,C,D,E, 8);
  SHA_MIX( 9,  6,  1, 11); SHA_RND2(E,A,B,C,D, 9);
  SHA_MIX(10,  7,  2, 12); SHA_RND2(D,E,A,B,C,10);
  SHA_MIX(11,  8,  3, 13); SHA_RND2(C,D,E,A,B,11);
  SHA_MIX(12,  9,  4, 14); SHA_RND2(B,C,D,E,A,12);
  SHA_MIX(13, 10,  5, 15); SHA_RND2(A,B,C,D,E,13);
  SHA_MIX(14, 11,  6,  0); SHA_RND2(E,A,B,C,D,14);
  SHA_MIX(15, 12,  7,  1); SHA_RND2(D,E,A,B,C,15);

  SHA_MIX( 0, 13,  8,  2); SHA_RND2(C,D,E,A,B, 0);
  SHA_MIX( 1, 14,  9,  3); SHA_RND2(B,C,D,E,A, 1);
  SHA_MIX( 2, 15, 10,  4); SHA_RND2(A,B,C,D,E, 2);
  SHA_MIX( 3,  0, 11,  5); SHA_RND2(E,A,B,C,D, 3);
  SHA_MIX( 4,  1, 12,  6); SHA_RND2(D,E,A,B,C, 4);
  SHA_MIX( 5,  2, 13,  7); SHA_RND2(C,D,E,A,B, 5);
  SHA_MIX( 6,  3, 14,  8); SHA_RND2(B,C,D,E,A, 6);
  SHA_MIX( 7,  4, 15,  9); SHA_RND2(A,B,C,D,E, 7);

  SHA_MIX( 8,  5,  0, 10); SHA_RND3(E,A,B,C,D, 8);
  SHA_MIX( 9,  6,  1, 11); SHA_RND3(D,E,A,B,C, 9);
  SHA_MIX(10,  7,  2, 12); SHA_RND3(C,D,E,A,B,10);
  SHA_MIX(11,  8,  3, 13); SHA_RND3(B,C,D,E,A,11);
  SHA_MIX(12,  9,  4, 14); SHA_RND3(A,B,C,D,E,12);
  SHA_MIX(13, 10,  5, 15); SHA_RND3(E,A,B,C,D,13);
  SHA_MIX(14, 11,  6,  0); SHA_RND3(D,E,A,B,C,14);
  SHA_MIX(15, 12,  7,  1); SHA_RND3(C,D,E,A,B,15);

  SHA_MIX( 0, 13,  8,  2); SHA_RND3(B,C,D,E,A, 0);
  SHA_MIX( 1, 14,  9,  3); SHA_RND3(A,B,C,D,E, 1);
  SHA_MIX( 2, 15, 10,  4); SHA_RND3(E,A,B,C,D, 2);
  SHA_MIX( 3,  0, 11,  5); SHA_RND3(D,E,A,B,C, 3);
  SHA_MIX( 4,  1, 12,  6); SHA_RND3(C,D,E,A,B, 4);
  SHA_MIX( 5,  2, 13,  7); SHA_RND3(B,C,D,E,A, 5);
  SHA_MIX( 6,  3, 14,  8); SHA_RND3(A,B,C,D,E, 6);
  SHA_MIX( 7,  4, 15,  9); SHA_RND3(E,A,B,C,D, 7);
  SHA_MIX( 8,  5,  0, 10); SHA_RND3(D,E,A,B,C, 8);
  SHA_MIX( 9,  6,  1, 11); SHA_RND3(C,D,E,A,B, 9);
  SHA_MIX(10,  7,  2, 12); SHA_RND3(B,C,D,E,A,10);
  SHA_MIX(11,  8,  3, 13); SHA_RND3(A,B,C,D,E,11);

  SHA_MIX(12,  9,  4, 14); SHA_RND4(E,A,B,C,D,12);
  SHA_MIX(13, 10,  5, 15); SHA_RND4(D,E,A,B,C,13);
  SHA_MIX(14, 11,  6,  0); SHA_RND4(C,D,E,A,B,14);
  SHA_MIX(15, 12,  7,  1); SHA_RND4(B,C,D,E,A,15);

  SHA_MIX( 0, 13,  8,  2); SHA_RND4(A,B,C,D,E, 0);
  SHA_MIX( 1, 14,  9,  3); SHA_RND4(E,A,B,C,D, 1);
  SHA_MIX( 2, 15, 10,  4); SHA_RND4(D,E,A,B,C, 2);
  SHA_MIX( 3,  0, 11,  5); SHA_RND4(C,D,E,A,B, 3);
  SHA_MIX( 4,  1, 12,  6); SHA_RND4(B,C,D,E,A, 4);
  SHA_MIX( 5,  2, 13,  7); SHA_RND4(A,B,C,D,E, 5);
  SHA_MIX( 6,  3, 14,  8); SHA_RND4(E,A,B,C,D, 6);
  SHA_MIX( 7,  4, 15,  9); SHA_RND4(D,E,A,B,C, 7);
  SHA_MIX( 8,  5,  0, 10); SHA_RND4(C,D,E,A,B, 8);
  SHA_MIX( 9,  6,  1, 11); SHA_RND4(B,C,D,E,A, 9);
  SHA_MIX(10,  7,  2, 12); SHA_RND4(A,B,C,D,E,10);
  SHA_MIX(11,  8,  3, 13); SHA_RND4(E,A,B,C,D,11);
  SHA_MIX(12,  9,  4, 14); SHA_RND4(D,E,A,B,C,12);
  SHA_MIX(13, 10,  5, 15); SHA_RND4(C,D,E,A,B,13);
  SHA_MIX(14, 11,  6,  0); SHA_RND4(B,C,D,E,A,14);
  SHA_MIX(15, 12,  7,  1); SHA_RND4(A,B,C,D,E,15);

  XH(0) += A;
  XH(1) += B;
  XH(2) += C;
  XH(3) += D;
  XH(4) += E;
}