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Diffstat (limited to 'third_party/bearssl/src/poly1305_i15.c')
| -rw-r--r-- | third_party/bearssl/src/poly1305_i15.c | 221 |
1 files changed, 221 insertions, 0 deletions
diff --git a/third_party/bearssl/src/poly1305_i15.c b/third_party/bearssl/src/poly1305_i15.c new file mode 100644 index 0000000..6f89212 --- /dev/null +++ b/third_party/bearssl/src/poly1305_i15.c @@ -0,0 +1,221 @@ +/* + * Copyright (c) 2017 Thomas Pornin <[email protected]> + * + * 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); + } +} |