poly1305.c

/*
 * Public Domain poly1305 from Andrew Moon
 * poly1305-donna-unrolled.c from https://github.com/floodyberry/poly1305-donna
 */

/* $OpenBSD: poly1305.c,v 1.3 2013/12/19 22:57:13 djm Exp $ */

#include "poly1305.h"

#define mul32x32_64(a, b) ((uint64_t)(a) * (b))

#define U8TO32_LE(p)                                                           \
  (((uint32_t)((p)[0])) | ((uint32_t)((p)[1]) << 8) |                          \
   ((uint32_t)((p)[2]) << 16) | ((uint32_t)((p)[3]) << 24))

#define U32TO8_LE(p, v)                                                        \
  do {                                                                         \
    (p)[0] = (uint8_t)((v));                                                   \
    (p)[1] = (uint8_t)((v) >> 8);                                              \
    (p)[2] = (uint8_t)((v) >> 16);                                             \
    (p)[3] = (uint8_t)((v) >> 24);                                             \
  } while (0)

void poly1305_auth(unsigned char out[POLY1305_TAGLEN], const unsigned char *m,
                   size_t inlen, const unsigned char key[POLY1305_KEYLEN]) {
  uint32_t t0, t1, t2, t3;
  uint32_t h0, h1, h2, h3, h4;
  uint32_t r0, r1, r2, r3, r4;
  uint32_t s1, s2, s3, s4;
  uint32_t b, nb;
  size_t j;
  uint64_t t[5];
  uint64_t f0, f1, f2, f3;
  uint32_t g0, g1, g2, g3, g4;
  uint64_t c;
  unsigned char mp[16];

  /* clamp key */
  t0 = U8TO32_LE(key + 0);
  t1 = U8TO32_LE(key + 4);
  t2 = U8TO32_LE(key + 8);
  t3 = U8TO32_LE(key + 12);

  /* precompute multipliers */
  r0 = t0 & 0x3ffffff;
  t0 >>= 26;
  t0 |= t1 << 6;
  r1 = t0 & 0x3ffff03;
  t1 >>= 20;
  t1 |= t2 << 12;
  r2 = t1 & 0x3ffc0ff;
  t2 >>= 14;
  t2 |= t3 << 18;
  r3 = t2 & 0x3f03fff;
  t3 >>= 8;
  r4 = t3 & 0x00fffff;

  s1 = r1 * 5;
  s2 = r2 * 5;
  s3 = r3 * 5;
  s4 = r4 * 5;

  /* init state */
  h0 = 0;
  h1 = 0;
  h2 = 0;
  h3 = 0;
  h4 = 0;

  /* full blocks */
  if (inlen < 16)
    goto poly1305_donna_atmost15bytes;
poly1305_donna_16bytes:
  m += 16;
  inlen -= 16;

  t0 = U8TO32_LE(m - 16);
  t1 = U8TO32_LE(m - 12);
  t2 = U8TO32_LE(m - 8);
  t3 = U8TO32_LE(m - 4);

  h0 += t0 & 0x3ffffff;
  h1 += ((((uint64_t)t1 << 32) | t0) >> 26) & 0x3ffffff;
  h2 += ((((uint64_t)t2 << 32) | t1) >> 20) & 0x3ffffff;
  h3 += ((((uint64_t)t3 << 32) | t2) >> 14) & 0x3ffffff;
  h4 += (t3 >> 8) | (1 << 24);

poly1305_donna_mul:
  t[0] = mul32x32_64(h0, r0) + mul32x32_64(h1, s4) + mul32x32_64(h2, s3) +
         mul32x32_64(h3, s2) + mul32x32_64(h4, s1);
  t[1] = mul32x32_64(h0, r1) + mul32x32_64(h1, r0) + mul32x32_64(h2, s4) +
         mul32x32_64(h3, s3) + mul32x32_64(h4, s2);
  t[2] = mul32x32_64(h0, r2) + mul32x32_64(h1, r1) + mul32x32_64(h2, r0) +
         mul32x32_64(h3, s4) + mul32x32_64(h4, s3);
  t[3] = mul32x32_64(h0, r3) + mul32x32_64(h1, r2) + mul32x32_64(h2, r1) +
         mul32x32_64(h3, r0) + mul32x32_64(h4, s4);
  t[4] = mul32x32_64(h0, r4) + mul32x32_64(h1, r3) + mul32x32_64(h2, r2) +
         mul32x32_64(h3, r1) + mul32x32_64(h4, r0);

  h0 = (uint32_t)t[0] & 0x3ffffff;
  c = (t[0] >> 26);
  t[1] += c;
  h1 = (uint32_t)t[1] & 0x3ffffff;
  b = (uint32_t)(t[1] >> 26);
  t[2] += b;
  h2 = (uint32_t)t[2] & 0x3ffffff;
  b = (uint32_t)(t[2] >> 26);
  t[3] += b;
  h3 = (uint32_t)t[3] & 0x3ffffff;
  b = (uint32_t)(t[3] >> 26);
  t[4] += b;
  h4 = (uint32_t)t[4] & 0x3ffffff;
  b = (uint32_t)(t[4] >> 26);
  h0 += b * 5;

  if (inlen >= 16)
    goto poly1305_donna_16bytes;

/* final bytes */
poly1305_donna_atmost15bytes:
  if (!inlen)
    goto poly1305_donna_finish;

  for (j = 0; j < inlen; j++)
    mp[j] = m[j];
  mp[j++] = 1;
  for (; j < 16; j++)
    mp[j] = 0;
  inlen = 0;

  t0 = U8TO32_LE(mp + 0);
  t1 = U8TO32_LE(mp + 4);
  t2 = U8TO32_LE(mp + 8);
  t3 = U8TO32_LE(mp + 12);

  h0 += t0 & 0x3ffffff;
  h1 += ((((uint64_t)t1 << 32) | t0) >> 26) & 0x3ffffff;
  h2 += ((((uint64_t)t2 << 32) | t1) >> 20) & 0x3ffffff;
  h3 += ((((uint64_t)t3 << 32) | t2) >> 14) & 0x3ffffff;
  h4 += (t3 >> 8);

  goto poly1305_donna_mul;

poly1305_donna_finish:
  b = h0 >> 26;
  h0 = h0 & 0x3ffffff;
  h1 += b;
  b = h1 >> 26;
  h1 = h1 & 0x3ffffff;
  h2 += b;
  b = h2 >> 26;
  h2 = h2 & 0x3ffffff;
  h3 += b;
  b = h3 >> 26;
  h3 = h3 & 0x3ffffff;
  h4 += b;
  b = h4 >> 26;
  h4 = h4 & 0x3ffffff;
  h0 += b * 5;
  b = h0 >> 26;
  h0 = h0 & 0x3ffffff;
  h1 += b;

  g0 = h0 + 5;
  b = g0 >> 26;
  g0 &= 0x3ffffff;
  g1 = h1 + b;
  b = g1 >> 26;
  g1 &= 0x3ffffff;
  g2 = h2 + b;
  b = g2 >> 26;
  g2 &= 0x3ffffff;
  g3 = h3 + b;
  b = g3 >> 26;
  g3 &= 0x3ffffff;
  g4 = h4 + b - (1 << 26);

  b = (g4 >> 31) - 1;
  nb = ~b;
  h0 = (h0 & nb) | (g0 & b);
  h1 = (h1 & nb) | (g1 & b);
  h2 = (h2 & nb) | (g2 & b);
  h3 = (h3 & nb) | (g3 & b);
  h4 = (h4 & nb) | (g4 & b);

  f0 = ((h0) | (h1 << 26)) + (uint64_t)U8TO32_LE(&key[16]);
  f1 = ((h1 >> 6) | (h2 << 20)) + (uint64_t)U8TO32_LE(&key[20]);
  f2 = ((h2 >> 12) | (h3 << 14)) + (uint64_t)U8TO32_LE(&key[24]);
  f3 = ((h3 >> 18) | (h4 << 8)) + (uint64_t)U8TO32_LE(&key[28]);

  U32TO8_LE(&out[0], f0);
  f1 += (f0 >> 32);
  U32TO8_LE(&out[4], f1);
  f2 += (f1 >> 32);
  U32TO8_LE(&out[8], f2);
  f3 += (f2 >> 32);
  U32TO8_LE(&out[12], f3);
}