+/*
+ * Copyright (c) 2017 Thomas Pornin <pornin@bolet.org>
+ *
+ * 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);
+ }
+}
projects / BearSSL / commitdiff