--- /dev/null
+/*
+ * 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"
+
+/*
+ * This is a "reference" implementation of Poly1305 that uses the
+ * generic "i15" code for big integers. It is slow, but it handles all
+ * big-integer operations with generic code, thereby avoiding most
+ * tricky situations with carry propagation and modular reduction.
+ */
+
+/*
+ * Modulus: 2^130-5.
+ */
+static const uint16_t P1305[] = {
+ 0x008A,
+ 0x7FFB, 0x7FFF, 0x7FFF, 0x7FFF, 0x7FFF, 0x7FFF, 0x7FFF, 0x7FFF, 0x03FF
+};
+
+/*
+ * -p mod 2^15.
+ */
+#define P0I 0x4CCD
+
+/*
+ * R^2 mod p, for conversion to Montgomery representation (R = 2^135,
+ * since we use 9 words of 15 bits each, and 15*9 = 135).
+ */
+static const uint16_t R2[] = {
+ 0x008A,
+ 0x6400, 0x0000, 0x0000, 0x0000, 0x0000, 0x0000, 0x0000, 0x0000, 0x0000
+};
+
+/*
+ * Perform the inner processing of blocks for Poly1305. The "r" array
+ * is in Montgomery representation, while the "a" array is not.
+ */
+static void
+poly1305_inner(uint16_t *a, const uint16_t *r, const void *data, size_t len)
+{
+ const unsigned char *buf;
+
+ buf = data;
+ while (len > 0) {
+ unsigned char tmp[16], rev[16];
+ uint16_t b[10];
+ uint32_t ctl;
+ int i;
+
+ /*
+ * 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". Since
+ * decoding is little-endian, we must byte-swap the buffer.
+ */
+ for (i = 0; i < 16; i ++) {
+ rev[i] = buf[15 - i];
+ }
+ br_i15_decode_mod(b, rev, sizeof rev, P1305);
+ b[9] |= 0x0100;
+
+ /*
+ * Add the accumulator to the decoded block (modular
+ * addition).
+ */
+ ctl = br_i15_add(b, a, 1);
+ ctl |= NOT(br_i15_sub(b, P1305, 0));
+ br_i15_sub(b, P1305, ctl);
+
+ /*
+ * Multiply by r, result is the new accumulator value.
+ */
+ br_i15_montymul(a, b, r, P1305, P0I);
+
+ buf += 16;
+ len -= 16;
+ }
+}
+
+/*
+ * Byteswap a 16-byte value.
+ */
+static void
+byteswap16(unsigned char *buf)
+{
+ int i;
+
+ for (i = 0; i < 8; i ++) {
+ unsigned x;
+
+ x = buf[i];
+ buf[i] = buf[15 - i];
+ buf[15 - i] = x;
+ }
+}
+
+/* see bearssl_block.h */
+void
+br_poly1305_i15_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];
+ uint16_t t[10], r[10], acc[10];
+
+ /*
+ * 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.
+ */
+
+ /*
+ * Apply the "clamping" operation on the encoded 'r' value.
+ */
+ pkey[ 3] &= 0x0F;
+ pkey[ 7] &= 0x0F;
+ pkey[11] &= 0x0F;
+ pkey[15] &= 0x0F;
+ pkey[ 4] &= 0xFC;
+ pkey[ 8] &= 0xFC;
+ pkey[12] &= 0xFC;
+
+ /*
+ * Decode the clamped 'r' value. Decoding should use little-endian
+ * so we must byteswap the value first.
+ */
+ byteswap16(pkey);
+ br_i15_decode_mod(t, pkey, 16, P1305);
+
+ /*
+ * Convert 'r' to Montgomery representation.
+ */
+ br_i15_montymul(r, t, R2, P1305, P0I);
+
+ /*
+ * Accumulator is 0.
+ */
+ br_i15_zero(acc, 0x8A);
+
+ /*
+ * 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);
+
+ /*
+ * Decode the value 's'. Again, a byteswap is needed.
+ */
+ byteswap16(pkey + 16);
+ br_i15_decode_mod(t, pkey + 16, 16, P1305);
+
+ /*
+ * Add the value 's' to the accumulator. That addition is done
+ * modulo 2^128, so we just ignore the carry.
+ */
+ br_i15_add(acc, t, 1);
+
+ /*
+ * Encode the result (128 low bits) to the tag. Encoding should
+ * be little-endian.
+ */
+ br_i15_encode(tag, 16, acc);
+ byteswap16(tag);
+
+ /*
+ * If decrypting, then ChaCha20 runs _after_ Poly1305.
+ */
+ if (!encrypt) {
+ ichacha(key, iv, 1, data, len);
+ }
+}
projects / BearSSL / blobdiff