poly1305.cpp

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// Copyright (c) 2019 The Bitcoin Core developers
// Distributed under the MIT software license, see the accompanying
// file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
// Based on the public domain implementation by Andrew Moon
// poly1305-donna-unrolled.c from https://github.com/floodyberry/poly1305-donna
 
#include <crypto/common.h>
#include <crypto/poly1305.h>
 
#include <cstring>
 
#define mul32x32_64(a, b) ((uint64_t)(a) * (b))
 
void poly1305_auth(uint8_t out[POLY1305_TAGLEN], const uint8_t *m, size_t inlen,
                   const uint8_t 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;
    uint64_t g0, g1, g2, g3, g4;
    uint64_t c;
    uint8_t mp[16];
 
    /* clamp key */
    t0 = ReadLE32(key + 0);
    t1 = ReadLE32(key + 4);
    t2 = ReadLE32(key + 8);
    t3 = ReadLE32(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 = ReadLE32(m - 16);
    t1 = ReadLE32(m - 12);
    t2 = ReadLE32(m - 8);
    t3 = ReadLE32(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 = ReadLE32(mp + 0);
    t1 = ReadLE32(mp + 4);
    t2 = ReadLE32(mp + 8);
    t3 = ReadLE32(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)ReadLE32(&key[16]);
    f1 = ((h1 >> 6) | (h2 << 20)) + (uint64_t)ReadLE32(&key[20]);
    f2 = ((h2 >> 12) | (h3 << 14)) + (uint64_t)ReadLE32(&key[24]);
    f3 = ((h3 >> 18) | (h4 << 8)) + (uint64_t)ReadLE32(&key[28]);
 
    WriteLE32(&out[0], f0);
    f1 += (f0 >> 32);
    WriteLE32(&out[4], f1);
    f2 += (f1 >> 32);
    WriteLE32(&out[8], f2);
    f3 += (f2 >> 32);
    WriteLE32(&out[12], f3);
}