diff options
Diffstat (limited to 'contrib/bearssl/src/ec/ecdsa_i31_vrfy_raw.c')
| -rw-r--r-- | contrib/bearssl/src/ec/ecdsa_i31_vrfy_raw.c | 165 |
1 files changed, 165 insertions, 0 deletions
diff --git a/contrib/bearssl/src/ec/ecdsa_i31_vrfy_raw.c b/contrib/bearssl/src/ec/ecdsa_i31_vrfy_raw.c new file mode 100644 index 000000000000..259477fdb8fc --- /dev/null +++ b/contrib/bearssl/src/ec/ecdsa_i31_vrfy_raw.c @@ -0,0 +1,165 @@ +/* + * 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" + +#define I31_LEN ((BR_MAX_EC_SIZE + 61) / 31) +#define POINT_LEN (1 + (((BR_MAX_EC_SIZE + 7) >> 3) << 1)) + +/* see bearssl_ec.h */ +uint32_t +br_ecdsa_i31_vrfy_raw(const br_ec_impl *impl, + const void *hash, size_t hash_len, + const br_ec_public_key *pk, + const void *sig, size_t sig_len) +{ + /* + * 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. + */ + const br_ec_curve_def *cd; + uint32_t n[I31_LEN], r[I31_LEN], s[I31_LEN], t1[I31_LEN], t2[I31_LEN]; + unsigned char tx[(BR_MAX_EC_SIZE + 7) >> 3]; + unsigned char ty[(BR_MAX_EC_SIZE + 7) >> 3]; + unsigned char eU[POINT_LEN]; + size_t nlen, rlen, ulen; + uint32_t n0i, res; + + /* + * If the curve is not supported, then report an error. + */ + if (((impl->supported_curves >> pk->curve) & 1) == 0) { + return 0; + } + + /* + * Get the curve parameters (generator and order). + */ + switch (pk->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; + } + + /* + * Signature length must be even. + */ + if (sig_len & 1) { + return 0; + } + rlen = sig_len >> 1; + + /* + * Public key point must have the proper size for this curve. + */ + if (pk->qlen != cd->generator_len) { + return 0; + } + + /* + * Get modulus; then decode the r and s values. They must be + * lower than the modulus, and s must not be null. + */ + nlen = cd->order_len; + br_i31_decode(n, cd->order, nlen); + n0i = br_i31_ninv31(n[1]); + if (!br_i31_decode_mod(r, sig, rlen, n)) { + return 0; + } + if (!br_i31_decode_mod(s, (const unsigned char *)sig + rlen, rlen, n)) { + return 0; + } + if (br_i31_iszero(s)) { + return 0; + } + + /* + * Invert s. We do that with a modular exponentiation; we use + * the fact that for all the curves we support, the least + * significant byte is not 0 or 1, so we can subtract 2 without + * any carry to process. + * We also want 1/s in Montgomery representation, which can be + * done by converting _from_ Montgomery representation before + * the inversion (because (1/s)*R = 1/(s/R)). + */ + br_i31_from_monty(s, n, n0i); + memcpy(tx, cd->order, nlen); + tx[nlen - 1] -= 2; + br_i31_modpow(s, tx, nlen, n, n0i, t1, t2); + + /* + * Truncate the hash to the modulus length (in bits) and reduce + * it modulo the curve order. The modular reduction can be done + * with a subtraction since the truncation already reduced the + * value to the modulus bit length. + */ + br_ecdsa_i31_bits2int(t1, hash, hash_len, n[0]); + br_i31_sub(t1, n, br_i31_sub(t1, n, 0) ^ 1); + + /* + * Multiply the (truncated, reduced) hash value with 1/s, result in + * t2, encoded in ty. + */ + br_i31_montymul(t2, t1, s, n, n0i); + br_i31_encode(ty, nlen, t2); + + /* + * Multiply r with 1/s, result in t1, encoded in tx. + */ + br_i31_montymul(t1, r, s, n, n0i); + br_i31_encode(tx, nlen, t1); + + /* + * Compute the point x*Q + y*G. + */ + ulen = cd->generator_len; + memcpy(eU, pk->q, ulen); + res = impl->muladd(eU, NULL, ulen, + tx, nlen, ty, nlen, cd->curve); + + /* + * Get the X coordinate, reduce modulo the curve order, and + * compare with the 'r' value. + * + * The modular reduction can be done with subtractions because + * we work with curves of prime order, so the curve order is + * close to the field order (Hasse's theorem). + */ + br_i31_zero(t1, n[0]); + br_i31_decode(t1, &eU[1], ulen >> 1); + t1[0] = n[0]; + br_i31_sub(t1, n, br_i31_sub(t1, n, 0) ^ 1); + res &= ~br_i31_sub(t1, r, 1); + res &= br_i31_iszero(t1); + return res; +} |