/*
* Copyright (c) 2016 Thomas Pornin
*
* Permission is hereby granted, free of charge, to any person obtaining
* a copy of this software and associated documentation files (the
* "Software"), to deal in the Software without restriction, including
* without limitation the rights to use, copy, modify, merge, publish,
* distribute, sublicense, and/or sell copies of the Software, and to
* permit persons to whom the Software is furnished to do so, subject to
* the following conditions:
*
* The above copyright notice and this permission notice shall be
* included in all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
* NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
* BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
* ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
* CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
* SOFTWARE.
*/
#include "inner.h"
/*
* Perform the inner processing of blocks for Poly1305. The accumulator
* and the r key are provided as arrays of 26-bit words (these words
* are allowed to have an extra bit, i.e. use 27 bits).
*
* On output, all accumulator words fit on 26 bits, except acc[1], which
* may be slightly larger (but by a very small amount only).
*/
static void
poly1305_inner(uint32_t *acc, const uint32_t *r, const void *data, size_t len)
{
/*
* Implementation notes: we split the 130-bit values into five
* 26-bit words. This gives us some space for carries.
*
* This code is inspired from the public-domain code available
* on:
* https://github.com/floodyberry/poly1305-donna
*
* Since we compute modulo 2^130-5, the "upper words" become
* low words with a factor of 5; that is, x*2^130 = x*5 mod p.
*/
const unsigned char *buf;
uint32_t a0, a1, a2, a3, a4;
uint32_t r0, r1, r2, r3, r4;
uint32_t u1, u2, u3, u4;
r0 = r[0];
r1 = r[1];
r2 = r[2];
r3 = r[3];
r4 = r[4];
u1 = r1 * 5;
u2 = r2 * 5;
u3 = r3 * 5;
u4 = r4 * 5;
a0 = acc[0];
a1 = acc[1];
a2 = acc[2];
a3 = acc[3];
a4 = acc[4];
buf = data;
while (len > 0) {
uint64_t w0, w1, w2, w3, w4;
uint64_t c;
unsigned char tmp[16];
/*
* If there is a partial block, right-pad it with zeros.
*/
if (len < 16) {
memset(tmp, 0, sizeof tmp);
memcpy(tmp, buf, len);
buf = tmp;
len = 16;
}
/*
* Decode next block and apply the "high bit"; that value
* is added to the accumulator.
*/
a0 += br_dec32le(buf) & 0x03FFFFFF;
a1 += (br_dec32le(buf + 3) >> 2) & 0x03FFFFFF;
a2 += (br_dec32le(buf + 6) >> 4) & 0x03FFFFFF;
a3 += (br_dec32le(buf + 9) >> 6) & 0x03FFFFFF;
a4 += (br_dec32le(buf + 12) >> 8) | 0x01000000;
/*
* Compute multiplication.
*/
#define M(x, y) ((uint64_t)(x) * (uint64_t)(y))
w0 = M(a0, r0) + M(a1, u4) + M(a2, u3) + M(a3, u2) + M(a4, u1);
w1 = M(a0, r1) + M(a1, r0) + M(a2, u4) + M(a3, u3) + M(a4, u2);
w2 = M(a0, r2) + M(a1, r1) + M(a2, r0) + M(a3, u4) + M(a4, u3);
w3 = M(a0, r3) + M(a1, r2) + M(a2, r1) + M(a3, r0) + M(a4, u4);
w4 = M(a0, r4) + M(a1, r3) + M(a2, r2) + M(a3, r1) + M(a4, r0);
#undef M
/*
* Perform some (partial) modular reduction. This step is
* enough to keep values in ranges such that there won't
* be carry overflows. Most of the reduction was done in
* the multiplication step (by using the 'u*' values, and
* using the fact that 2^130 = -5 mod p); here we perform
* some carry propagation.
*/
c = w0 >> 26;
a0 = (uint32_t)w0 & 0x3FFFFFF;
w1 += c;
c = w1 >> 26;
a1 = (uint32_t)w1 & 0x3FFFFFF;
w2 += c;
c = w2 >> 26;
a2 = (uint32_t)w2 & 0x3FFFFFF;
w3 += c;
c = w3 >> 26;
a3 = (uint32_t)w3 & 0x3FFFFFF;
w4 += c;
c = w4 >> 26;
a4 = (uint32_t)w4 & 0x3FFFFFF;
a0 += (uint32_t)c * 5;
a1 += a0 >> 26;
a0 &= 0x3FFFFFF;
buf += 16;
len -= 16;
}
acc[0] = a0;
acc[1] = a1;
acc[2] = a2;
acc[3] = a3;
acc[4] = a4;
}
/* see bearssl_block.h */
void
br_poly1305_ctmul_run(const void *key, const void *iv,
void *data, size_t len, const void *aad, size_t aad_len,
void *tag, br_chacha20_run ichacha, int encrypt)
{
unsigned char pkey[32], foot[16];
uint32_t r[5], acc[5], cc, ctl, hi;
uint64_t w;
int i;
/*
* Compute the MAC key. The 'r' value is the first 16 bytes of
* pkey[].
*/
memset(pkey, 0, sizeof pkey);
ichacha(key, iv, 0, pkey, sizeof pkey);
/*
* If encrypting, ChaCha20 must run first, followed by Poly1305.
* When decrypting, the operations are reversed.
*/
if (encrypt) {
ichacha(key, iv, 1, data, len);
}
/*
* Run Poly1305. We must process the AAD, then ciphertext, then
* the footer (with the lengths). Note that the AAD and ciphertext
* are meant to be padded with zeros up to the next multiple of 16,
* and the length of the footer is 16 bytes as well.
*/
/*
* Decode the 'r' value into 26-bit words, with the "clamping"
* operation applied.
*/
r[0] = br_dec32le(pkey) & 0x03FFFFFF;
r[1] = (br_dec32le(pkey + 3) >> 2) & 0x03FFFF03;
r[2] = (br_dec32le(pkey + 6) >> 4) & 0x03FFC0FF;
r[3] = (br_dec32le(pkey + 9) >> 6) & 0x03F03FFF;
r[4] = (br_dec32le(pkey + 12) >> 8) & 0x000FFFFF;
/*
* Accumulator is 0.
*/
memset(acc, 0, sizeof acc);
/*
* Process the additional authenticated data, ciphertext, and
* footer in due order.
*/
br_enc64le(foot, (uint64_t)aad_len);
br_enc64le(foot + 8, (uint64_t)len);
poly1305_inner(acc, r, aad, aad_len);
poly1305_inner(acc, r, data, len);
poly1305_inner(acc, r, foot, sizeof foot);
/*
* Finalise modular reduction. This is done with carry propagation
* and applying the '2^130 = -5 mod p' rule. Note that the output
* of poly1035_inner() is already mostly reduced, since only
* acc[1] may be (very slightly) above 2^26. A single loop back
* to acc[1] will be enough to make the value fit in 130 bits.
*/
cc = 0;
for (i = 1; i <= 6; i ++) {
int j;
j = (i >= 5) ? i - 5 : i;
acc[j] += cc;
cc = acc[j] >> 26;
acc[j] &= 0x03FFFFFF;
}
/*
* We may still have a value in the 2^130-5..2^130-1 range, in
* which case we must reduce it again. The code below selects,
* in constant-time, between 'acc' and 'acc-p',
*/
ctl = GT(acc[0], 0x03FFFFFA);
for (i = 1; i < 5; i ++) {
ctl &= EQ(acc[i], 0x03FFFFFF);
}
cc = 5;
for (i = 0; i < 5; i ++) {
uint32_t t;
t = (acc[i] + cc);
cc = t >> 26;
t &= 0x03FFFFFF;
acc[i] = MUX(ctl, t, acc[i]);
}
/*
* Convert back the accumulator to 32-bit words, and add the
* 's' value (second half of pkey[]). That addition is done
* modulo 2^128.
*/
w = (uint64_t)acc[0] + ((uint64_t)acc[1] << 26) + br_dec32le(pkey + 16);
br_enc32le((unsigned char *)tag, (uint32_t)w);
w = (w >> 32) + ((uint64_t)acc[2] << 20) + br_dec32le(pkey + 20);
br_enc32le((unsigned char *)tag + 4, (uint32_t)w);
w = (w >> 32) + ((uint64_t)acc[3] << 14) + br_dec32le(pkey + 24);
br_enc32le((unsigned char *)tag + 8, (uint32_t)w);
hi = (uint32_t)(w >> 32) + (acc[4] << 8) + br_dec32le(pkey + 28);
br_enc32le((unsigned char *)tag + 12, hi);
/*
* If decrypting, then ChaCha20 runs _after_ Poly1305.
*/
if (!encrypt) {
ichacha(key, iv, 1, data, len);
}
}