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Diffstat (limited to 'crypto/secp256k1/libsecp256k1/src/ecdsa_impl.h')
| -rw-r--r-- | crypto/secp256k1/libsecp256k1/src/ecdsa_impl.h | 264 |
1 files changed, 264 insertions, 0 deletions
diff --git a/crypto/secp256k1/libsecp256k1/src/ecdsa_impl.h b/crypto/secp256k1/libsecp256k1/src/ecdsa_impl.h new file mode 100644 index 000000000..4a172b3c5 --- /dev/null +++ b/crypto/secp256k1/libsecp256k1/src/ecdsa_impl.h @@ -0,0 +1,264 @@ +/********************************************************************** + * Copyright (c) 2013, 2014 Pieter Wuille * + * Distributed under the MIT software license, see the accompanying * + * file COPYING or http://www.opensource.org/licenses/mit-license.php.* + **********************************************************************/ + + +#ifndef _SECP256K1_ECDSA_IMPL_H_ +#define _SECP256K1_ECDSA_IMPL_H_ + +#include "scalar.h" +#include "field.h" +#include "group.h" +#include "ecmult.h" +#include "ecmult_gen.h" +#include "ecdsa.h" + +/** Group order for secp256k1 defined as 'n' in "Standards for Efficient Cryptography" (SEC2) 2.7.1 + * sage: for t in xrange(1023, -1, -1): + * .. p = 2**256 - 2**32 - t + * .. if p.is_prime(): + * .. print '%x'%p + * .. break + * 'fffffffffffffffffffffffffffffffffffffffffffffffffffffffefffffc2f' + * sage: a = 0 + * sage: b = 7 + * sage: F = FiniteField (p) + * sage: '%x' % (EllipticCurve ([F (a), F (b)]).order()) + * 'fffffffffffffffffffffffffffffffebaaedce6af48a03bbfd25e8cd0364141' + */ +static const secp256k1_fe secp256k1_ecdsa_const_order_as_fe = SECP256K1_FE_CONST( + 0xFFFFFFFFUL, 0xFFFFFFFFUL, 0xFFFFFFFFUL, 0xFFFFFFFEUL, + 0xBAAEDCE6UL, 0xAF48A03BUL, 0xBFD25E8CUL, 0xD0364141UL +); + +/** Difference between field and order, values 'p' and 'n' values defined in + * "Standards for Efficient Cryptography" (SEC2) 2.7.1. + * sage: p = 0xFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFEFFFFFC2F + * sage: a = 0 + * sage: b = 7 + * sage: F = FiniteField (p) + * sage: '%x' % (p - EllipticCurve ([F (a), F (b)]).order()) + * '14551231950b75fc4402da1722fc9baee' + */ +static const secp256k1_fe secp256k1_ecdsa_const_p_minus_order = SECP256K1_FE_CONST( + 0, 0, 0, 1, 0x45512319UL, 0x50B75FC4UL, 0x402DA172UL, 0x2FC9BAEEUL +); + +static int secp256k1_ecdsa_sig_parse(secp256k1_scalar *rr, secp256k1_scalar *rs, const unsigned char *sig, size_t size) { + unsigned char ra[32] = {0}, sa[32] = {0}; + const unsigned char *rp; + const unsigned char *sp; + size_t lenr; + size_t lens; + int overflow; + if (sig[0] != 0x30) { + return 0; + } + lenr = sig[3]; + if (5+lenr >= size) { + return 0; + } + lens = sig[lenr+5]; + if (sig[1] != lenr+lens+4) { + return 0; + } + if (lenr+lens+6 > size) { + return 0; + } + if (sig[2] != 0x02) { + return 0; + } + if (lenr == 0) { + return 0; + } + if (sig[lenr+4] != 0x02) { + return 0; + } + if (lens == 0) { + return 0; + } + sp = sig + 6 + lenr; + while (lens > 0 && sp[0] == 0) { + lens--; + sp++; + } + if (lens > 32) { + return 0; + } + rp = sig + 4; + while (lenr > 0 && rp[0] == 0) { + lenr--; + rp++; + } + if (lenr > 32) { + return 0; + } + memcpy(ra + 32 - lenr, rp, lenr); + memcpy(sa + 32 - lens, sp, lens); + overflow = 0; + secp256k1_scalar_set_b32(rr, ra, &overflow); + if (overflow) { + return 0; + } + secp256k1_scalar_set_b32(rs, sa, &overflow); + if (overflow) { + return 0; + } + return 1; +} + +static int secp256k1_ecdsa_sig_serialize(unsigned char *sig, size_t *size, const secp256k1_scalar* ar, const secp256k1_scalar* as) { + unsigned char r[33] = {0}, s[33] = {0}; + unsigned char *rp = r, *sp = s; + size_t lenR = 33, lenS = 33; + secp256k1_scalar_get_b32(&r[1], ar); + secp256k1_scalar_get_b32(&s[1], as); + while (lenR > 1 && rp[0] == 0 && rp[1] < 0x80) { lenR--; rp++; } + while (lenS > 1 && sp[0] == 0 && sp[1] < 0x80) { lenS--; sp++; } + if (*size < 6+lenS+lenR) { + *size = 6 + lenS + lenR; + return 0; + } + *size = 6 + lenS + lenR; + sig[0] = 0x30; + sig[1] = 4 + lenS + lenR; + sig[2] = 0x02; + sig[3] = lenR; + memcpy(sig+4, rp, lenR); + sig[4+lenR] = 0x02; + sig[5+lenR] = lenS; + memcpy(sig+lenR+6, sp, lenS); + return 1; +} + +static int secp256k1_ecdsa_sig_verify(const secp256k1_ecmult_context *ctx, const secp256k1_scalar *sigr, const secp256k1_scalar *sigs, const secp256k1_ge *pubkey, const secp256k1_scalar *message) { + unsigned char c[32]; + secp256k1_scalar sn, u1, u2; + secp256k1_fe xr; + secp256k1_gej pubkeyj; + secp256k1_gej pr; + + if (secp256k1_scalar_is_zero(sigr) || secp256k1_scalar_is_zero(sigs)) { + return 0; + } + + secp256k1_scalar_inverse_var(&sn, sigs); + secp256k1_scalar_mul(&u1, &sn, message); + secp256k1_scalar_mul(&u2, &sn, sigr); + secp256k1_gej_set_ge(&pubkeyj, pubkey); + secp256k1_ecmult(ctx, &pr, &pubkeyj, &u2, &u1); + if (secp256k1_gej_is_infinity(&pr)) { + return 0; + } + secp256k1_scalar_get_b32(c, sigr); + secp256k1_fe_set_b32(&xr, c); + + /** We now have the recomputed R point in pr, and its claimed x coordinate (modulo n) + * in xr. Naively, we would extract the x coordinate from pr (requiring a inversion modulo p), + * compute the remainder modulo n, and compare it to xr. However: + * + * xr == X(pr) mod n + * <=> exists h. (xr + h * n < p && xr + h * n == X(pr)) + * [Since 2 * n > p, h can only be 0 or 1] + * <=> (xr == X(pr)) || (xr + n < p && xr + n == X(pr)) + * [In Jacobian coordinates, X(pr) is pr.x / pr.z^2 mod p] + * <=> (xr == pr.x / pr.z^2 mod p) || (xr + n < p && xr + n == pr.x / pr.z^2 mod p) + * [Multiplying both sides of the equations by pr.z^2 mod p] + * <=> (xr * pr.z^2 mod p == pr.x) || (xr + n < p && (xr + n) * pr.z^2 mod p == pr.x) + * + * Thus, we can avoid the inversion, but we have to check both cases separately. + * secp256k1_gej_eq_x implements the (xr * pr.z^2 mod p == pr.x) test. + */ + if (secp256k1_gej_eq_x_var(&xr, &pr)) { + /* xr.x == xr * xr.z^2 mod p, so the signature is valid. */ + return 1; + } + if (secp256k1_fe_cmp_var(&xr, &secp256k1_ecdsa_const_p_minus_order) >= 0) { + /* xr + p >= n, so we can skip testing the second case. */ + return 0; + } + secp256k1_fe_add(&xr, &secp256k1_ecdsa_const_order_as_fe); + if (secp256k1_gej_eq_x_var(&xr, &pr)) { + /* (xr + n) * pr.z^2 mod p == pr.x, so the signature is valid. */ + return 1; + } + return 0; +} + +static int secp256k1_ecdsa_sig_recover(const secp256k1_ecmult_context *ctx, const secp256k1_scalar *sigr, const secp256k1_scalar* sigs, secp256k1_ge *pubkey, const secp256k1_scalar *message, int recid) { + unsigned char brx[32]; + secp256k1_fe fx; + secp256k1_ge x; + secp256k1_gej xj; + secp256k1_scalar rn, u1, u2; + secp256k1_gej qj; + + if (secp256k1_scalar_is_zero(sigr) || secp256k1_scalar_is_zero(sigs)) { + return 0; + } + + secp256k1_scalar_get_b32(brx, sigr); + VERIFY_CHECK(secp256k1_fe_set_b32(&fx, brx)); /* brx comes from a scalar, so is less than the order; certainly less than p */ + if (recid & 2) { + if (secp256k1_fe_cmp_var(&fx, &secp256k1_ecdsa_const_p_minus_order) >= 0) { + return 0; + } + secp256k1_fe_add(&fx, &secp256k1_ecdsa_const_order_as_fe); + } + if (!secp256k1_ge_set_xo_var(&x, &fx, recid & 1)) { + return 0; + } + secp256k1_gej_set_ge(&xj, &x); + secp256k1_scalar_inverse_var(&rn, sigr); + secp256k1_scalar_mul(&u1, &rn, message); + secp256k1_scalar_negate(&u1, &u1); + secp256k1_scalar_mul(&u2, &rn, sigs); + secp256k1_ecmult(ctx, &qj, &xj, &u2, &u1); + secp256k1_ge_set_gej_var(pubkey, &qj); + return !secp256k1_gej_is_infinity(&qj); +} + +static int secp256k1_ecdsa_sig_sign(const secp256k1_ecmult_gen_context *ctx, secp256k1_scalar *sigr, secp256k1_scalar *sigs, const secp256k1_scalar *seckey, const secp256k1_scalar *message, const secp256k1_scalar *nonce, int *recid) { + unsigned char b[32]; + secp256k1_gej rp; + secp256k1_ge r; + secp256k1_scalar n; + int overflow = 0; + + secp256k1_ecmult_gen(ctx, &rp, nonce); + secp256k1_ge_set_gej(&r, &rp); + secp256k1_fe_normalize(&r.x); + secp256k1_fe_normalize(&r.y); + secp256k1_fe_get_b32(b, &r.x); + secp256k1_scalar_set_b32(sigr, b, &overflow); + if (secp256k1_scalar_is_zero(sigr)) { + /* P.x = order is on the curve, so technically sig->r could end up zero, which would be an invalid signature. */ + secp256k1_gej_clear(&rp); + secp256k1_ge_clear(&r); + return 0; + } + if (recid) { + *recid = (overflow ? 2 : 0) | (secp256k1_fe_is_odd(&r.y) ? 1 : 0); + } + secp256k1_scalar_mul(&n, sigr, seckey); + secp256k1_scalar_add(&n, &n, message); + secp256k1_scalar_inverse(sigs, nonce); + secp256k1_scalar_mul(sigs, sigs, &n); + secp256k1_scalar_clear(&n); + secp256k1_gej_clear(&rp); + secp256k1_ge_clear(&r); + if (secp256k1_scalar_is_zero(sigs)) { + return 0; + } + if (secp256k1_scalar_is_high(sigs)) { + secp256k1_scalar_negate(sigs, sigs); + if (recid) { + *recid ^= 1; + } + } + return 1; +} + +#endif |