diff options
Diffstat (limited to 'third_party/bearssl/src/ecdsa_i15_sign_raw.c')
| -rw-r--r-- | third_party/bearssl/src/ecdsa_i15_sign_raw.c | 174 |
1 files changed, 174 insertions, 0 deletions
diff --git a/third_party/bearssl/src/ecdsa_i15_sign_raw.c b/third_party/bearssl/src/ecdsa_i15_sign_raw.c new file mode 100644 index 0000000..39b2e1d --- /dev/null +++ b/third_party/bearssl/src/ecdsa_i15_sign_raw.c @@ -0,0 +1,174 @@ +/* + * 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" + +#define I15_LEN ((BR_MAX_EC_SIZE + 29) / 15) +#define POINT_LEN (1 + (((BR_MAX_EC_SIZE + 7) >> 3) << 1)) +#define ORDER_LEN ((BR_MAX_EC_SIZE + 7) >> 3) + +/* see bearssl_ec.h */ +size_t +br_ecdsa_i15_sign_raw(const br_ec_impl *impl, + const br_hash_class *hf, const void *hash_value, + const br_ec_private_key *sk, void *sig) +{ + /* + * IMPORTANT: this code is fit only for curves with a prime + * order. This is needed so that modular reduction of the X + * coordinate of a point can be done with a simple subtraction. + * We also rely on the last byte of the curve order to be distinct + * from 0 and 1. + */ + const br_ec_curve_def *cd; + uint16_t n[I15_LEN], r[I15_LEN], s[I15_LEN], x[I15_LEN]; + uint16_t m[I15_LEN], k[I15_LEN], t1[I15_LEN], t2[I15_LEN]; + unsigned char tt[ORDER_LEN << 1]; + unsigned char eU[POINT_LEN]; + size_t hash_len, nlen, ulen; + uint16_t n0i; + uint32_t ctl; + br_hmac_drbg_context drbg; + + /* + * If the curve is not supported, then exit with an error. + */ + if (((impl->supported_curves >> sk->curve) & 1) == 0) { + return 0; + } + + /* + * Get the curve parameters (generator and order). + */ + switch (sk->curve) { + case BR_EC_secp256r1: + cd = &br_secp256r1; + break; + case BR_EC_secp384r1: + cd = &br_secp384r1; + break; + case BR_EC_secp521r1: + cd = &br_secp521r1; + break; + default: + return 0; + } + + /* + * Get modulus. + */ + nlen = cd->order_len; + br_i15_decode(n, cd->order, nlen); + n0i = br_i15_ninv15(n[1]); + + /* + * Get private key as an i15 integer. This also checks that the + * private key is well-defined (not zero, and less than the + * curve order). + */ + if (!br_i15_decode_mod(x, sk->x, sk->xlen, n)) { + return 0; + } + if (br_i15_iszero(x)) { + return 0; + } + + /* + * Get hash length. + */ + hash_len = (hf->desc >> BR_HASHDESC_OUT_OFF) & BR_HASHDESC_OUT_MASK; + + /* + * Truncate and reduce the hash value modulo the curve order. + */ + br_ecdsa_i15_bits2int(m, hash_value, hash_len, n[0]); + br_i15_sub(m, n, br_i15_sub(m, n, 0) ^ 1); + + /* + * RFC 6979 generation of the "k" value. + * + * The process uses HMAC_DRBG (with the hash function used to + * process the message that is to be signed). The seed is the + * concatenation of the encodings of the private key and + * the hash value (after truncation and modular reduction). + */ + br_i15_encode(tt, nlen, x); + br_i15_encode(tt + nlen, nlen, m); + br_hmac_drbg_init(&drbg, hf, tt, nlen << 1); + for (;;) { + br_hmac_drbg_generate(&drbg, tt, nlen); + br_ecdsa_i15_bits2int(k, tt, nlen, n[0]); + if (br_i15_iszero(k)) { + continue; + } + if (br_i15_sub(k, n, 0)) { + break; + } + } + + /* + * Compute k*G and extract the X coordinate, then reduce it + * modulo the curve order. Since we support only curves with + * prime order, that reduction is only a matter of computing + * a subtraction. + */ + br_i15_encode(tt, nlen, k); + ulen = impl->mulgen(eU, tt, nlen, sk->curve); + br_i15_zero(r, n[0]); + br_i15_decode(r, &eU[1], ulen >> 1); + r[0] = n[0]; + br_i15_sub(r, n, br_i15_sub(r, n, 0) ^ 1); + + /* + * Compute 1/k in double-Montgomery representation. We do so by + * first converting _from_ Montgomery representation (twice), + * then using a modular exponentiation. + */ + br_i15_from_monty(k, n, n0i); + br_i15_from_monty(k, n, n0i); + memcpy(tt, cd->order, nlen); + tt[nlen - 1] -= 2; + br_i15_modpow(k, tt, nlen, n, n0i, t1, t2); + + /* + * Compute s = (m+xr)/k (mod n). + * The k[] array contains R^2/k (double-Montgomery representation); + * we thus can use direct Montgomery multiplications and conversions + * from Montgomery, avoiding any call to br_i15_to_monty() (which + * is slower). + */ + br_i15_from_monty(m, n, n0i); + br_i15_montymul(t1, x, r, n, n0i); + ctl = br_i15_add(t1, m, 1); + ctl |= br_i15_sub(t1, n, 0) ^ 1; + br_i15_sub(t1, n, ctl); + br_i15_montymul(s, t1, k, n, n0i); + + /* + * Encode r and s in the signature. + */ + br_i15_encode(sig, nlen, r); + br_i15_encode((unsigned char *)sig + nlen, nlen, s); + return nlen << 1; +} |