/*
* Copyright (c) 2017 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.
*/
static void
poly1305_inner(uint32_t *a, const uint32_t *r, const void *data, size_t len)
{
/*
* Implementation notes: we split the 130-bit values into ten
* 13-bit words. This gives us some space for carries and allows
* using only 32x32->32 multiplications, which are way faster than
* 32x32->64 multiplications on the ARM Cortex-M0/M0+, and also
* help in making constant-time code on the Cortex-M3.
*
* 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.
* This has already been integrated in the r[] array, which
* is extended to the 0..18 range.
*
* In each loop iteration, a[] and r[] words are 13-bit each,
* except a[1] which may use 14 bits.
*/
const unsigned char *buf;
buf = data;
while (len > 0) {
unsigned char tmp[16];
uint32_t b[10];
unsigned u, v;
uint32_t z, cc1, cc2;
/*
* 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.
*/
v = br_dec16le(buf);
a[0] += v & 0x01FFF;
v >>= 13;
v |= buf[2] << 3;
v |= buf[3] << 11;
a[1] += v & 0x01FFF;
v >>= 13;
v |= buf[4] << 6;
a[2] += v & 0x01FFF;
v >>= 13;
v |= buf[5] << 1;
v |= buf[6] << 9;
a[3] += v & 0x01FFF;
v >>= 13;
v |= buf[7] << 4;
v |= buf[8] << 12;
a[4] += v & 0x01FFF;
v >>= 13;
v |= buf[9] << 7;
a[5] += v & 0x01FFF;
v >>= 13;
v |= buf[10] << 2;
v |= buf[11] << 10;
a[6] += v & 0x01FFF;
v >>= 13;
v |= buf[12] << 5;
a[7] += v & 0x01FFF;
v = br_dec16le(buf + 13);
a[8] += v & 0x01FFF;
v >>= 13;
v |= buf[15] << 3;
a[9] += v | 0x00800;
/*
* At that point, all a[] values fit on 14 bits, while
* all r[] values fit on 13 bits. Thus products fit on
* 27 bits, and we can accumulate up to 31 of them in
* a 32-bit word and still have some room for carries.
*/
/*
* Now a[] contains words with values up to 14 bits each.
* We perform the multiplication with r[].
*
* The extended words of r[] may be larger than 13 bits
* (they are 5 times a 13-bit word) so the full summation
* may yield values up to 46 times a 27-bit word, which
* does not fit on a 32-bit word. To avoid that issue, we
* must split the loop below in two, with a carry
* propagation operation in the middle.
*/
cc1 = 0;
for (u = 0; u < 10; u ++) {
uint32_t s;
s = cc1
+ MUL15(a[0], r[u + 9 - 0])
+ MUL15(a[1], r[u + 9 - 1])
+ MUL15(a[2], r[u + 9 - 2])
+ MUL15(a[3], r[u + 9 - 3])
+ MUL15(a[4], r[u + 9 - 4]);
b[u] = s & 0x1FFF;
cc1 = s >> 13;
}
cc2 = 0;
for (u = 0; u < 10; u ++) {
uint32_t s;
s = b[u] + cc2
+ MUL15(a[5], r[u + 9 - 5])
+ MUL15(a[6], r[u + 9 - 6])
+ MUL15(a[7], r[u + 9 - 7])
+ MUL15(a[8], r[u + 9 - 8])
+ MUL15(a[9], r[u + 9 - 9]);
b[u] = s & 0x1FFF;
cc2 = s >> 13;
}
memcpy(a, b, sizeof b);
/*
* The two carries "loop back" with a factor of 5. We
* propagate them into a[0] and a[1].
*/
z = cc1 + cc2;
z += (z << 2) + a[0];
a[0] = z & 0x1FFF;
a[1] += z >> 13;
buf += 16;
len -= 16;
}
}
/* see bearssl_block.h */
void
br_poly1305_ctmul32_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 z, r[19], acc[10], cc, ctl;
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 13-bit words, with the "clamping"
* operation applied.
*/
z = br_dec32le(pkey) & 0x03FFFFFF;
r[9] = z & 0x1FFF;
r[10] = z >> 13;
z = (br_dec32le(pkey + 3) >> 2) & 0x03FFFF03;
r[11] = z & 0x1FFF;
r[12] = z >> 13;
z = (br_dec32le(pkey + 6) >> 4) & 0x03FFC0FF;
r[13] = z & 0x1FFF;
r[14] = z >> 13;
z = (br_dec32le(pkey + 9) >> 6) & 0x03F03FFF;
r[15] = z & 0x1FFF;
r[16] = z >> 13;
z = (br_dec32le(pkey + 12) >> 8) & 0x000FFFFF;
r[17] = z & 0x1FFF;
r[18] = z >> 13;
/*
* Extend r[] with the 5x factor pre-applied.
*/
for (i = 0; i < 9; i ++) {
r[i] = MUL15(5, r[i + 10]);
}
/*
* 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 2^13. A single loop back
* to acc[1] will be enough to make the value fit in 130 bits.
*/
cc = 0;
for (i = 1; i < 10; i ++) {
z = acc[i] + cc;
acc[i] = z & 0x1FFF;
cc = z >> 13;
}
z = acc[0] + cc + (cc << 2);
acc[0] = z & 0x1FFF;
acc[1] += z >> 13;
/*
* 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], 0x1FFA);
for (i = 1; i < 10; i ++) {
ctl &= EQ(acc[i], 0x1FFF);
}
acc[0] = MUX(ctl, acc[0] - 0x1FFB, acc[0]);
for (i = 1; i < 10; i ++) {
acc[i] &= ~(-ctl);
}
/*
* Convert back the accumulator to 32-bit words, and add the
* 's' value (second half of pkey[]). That addition is done
* modulo 2^128.
*/
z = acc[0] + (acc[1] << 13) + br_dec16le(pkey + 16);
br_enc16le((unsigned char *)tag, z & 0xFFFF);
z = (z >> 16) + (acc[2] << 10) + br_dec16le(pkey + 18);
br_enc16le((unsigned char *)tag + 2, z & 0xFFFF);
z = (z >> 16) + (acc[3] << 7) + br_dec16le(pkey + 20);
br_enc16le((unsigned char *)tag + 4, z & 0xFFFF);
z = (z >> 16) + (acc[4] << 4) + br_dec16le(pkey + 22);
br_enc16le((unsigned char *)tag + 6, z & 0xFFFF);
z = (z >> 16) + (acc[5] << 1) + (acc[6] << 14) + br_dec16le(pkey + 24);
br_enc16le((unsigned char *)tag + 8, z & 0xFFFF);
z = (z >> 16) + (acc[7] << 11) + br_dec16le(pkey + 26);
br_enc16le((unsigned char *)tag + 10, z & 0xFFFF);
z = (z >> 16) + (acc[8] << 8) + br_dec16le(pkey + 28);
br_enc16le((unsigned char *)tag + 12, z & 0xFFFF);
z = (z >> 16) + (acc[9] << 5) + br_dec16le(pkey + 30);
br_enc16le((unsigned char *)tag + 14, z & 0xFFFF);
/*
* If decrypting, then ChaCha20 runs _after_ Poly1305.
*/
if (!encrypt) {
ichacha(key, iv, 1, data, len);
}
}