--- /dev/null
+/*
+ * Copyright (c) 2016 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. 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);
+ }
+}
projects / BearSSL / blobdiff