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Diffstat (limited to 'src/modules/schnorr/schnorr_impl.h')
-rw-r--r-- | src/modules/schnorr/schnorr_impl.h | 207 |
1 files changed, 0 insertions, 207 deletions
diff --git a/src/modules/schnorr/schnorr_impl.h b/src/modules/schnorr/schnorr_impl.h deleted file mode 100644 index e13ab6db7c..0000000000 --- a/src/modules/schnorr/schnorr_impl.h +++ /dev/null @@ -1,207 +0,0 @@ -/*********************************************************************** - * Copyright (c) 2014-2015 Pieter Wuille * - * Distributed under the MIT software license, see the accompanying * - * file COPYING or http://www.opensource.org/licenses/mit-license.php. * - ***********************************************************************/ - -#ifndef _SECP256K1_SCHNORR_IMPL_H_ -#define _SECP256K1_SCHNORR_IMPL_H_ - -#include <string.h> - -#include "schnorr.h" -#include "num.h" -#include "field.h" -#include "group.h" -#include "ecmult.h" -#include "ecmult_gen.h" - -/** - * Custom Schnorr-based signature scheme. They support multiparty signing, public key - * recovery and batch validation. - * - * Rationale for verifying R's y coordinate: - * In order to support batch validation and public key recovery, the full R point must - * be known to verifiers, rather than just its x coordinate. In order to not risk - * being more strict in batch validation than normal validation, validators must be - * required to reject signatures with incorrect y coordinate. This is only possible - * by including a (relatively slow) field inverse, or a field square root. However, - * batch validation offers potentially much higher benefits than this cost. - * - * Rationale for having an implicit y coordinate oddness: - * If we commit to having the full R point known to verifiers, there are two mechanism. - * Either include its oddness in the signature, or give it an implicit fixed value. - * As the R y coordinate can be flipped by a simple negation of the nonce, we choose the - * latter, as it comes with nearly zero impact on signing or validation performance, and - * saves a byte in the signature. - * - * Signing: - * Inputs: 32-byte message m, 32-byte scalar key x (!=0), 32-byte scalar nonce k (!=0) - * - * Compute point R = k * G. Reject nonce if R's y coordinate is odd (or negate nonce). - * Compute 32-byte r, the serialization of R's x coordinate. - * Compute scalar h = Hash(r || m). Reject nonce if h == 0 or h >= order. - * Compute scalar s = k - h * x. - * The signature is (r, s). - * - * - * Verification: - * Inputs: 32-byte message m, public key point Q, signature: (32-byte r, scalar s) - * - * Signature is invalid if s >= order. - * Signature is invalid if r >= p. - * Compute scalar h = Hash(r || m). Signature is invalid if h == 0 or h >= order. - * Option 1 (faster for single verification): - * Compute point R = h * Q + s * G. Signature is invalid if R is infinity or R's y coordinate is odd. - * Signature is valid if the serialization of R's x coordinate equals r. - * Option 2 (allows batch validation and pubkey recovery): - * Decompress x coordinate r into point R, with odd y coordinate. Fail if R is not on the curve. - * Signature is valid if R + h * Q + s * G == 0. - */ - -static int secp256k1_schnorr_sig_sign(const secp256k1_ecmult_gen_context* ctx, unsigned char *sig64, const secp256k1_scalar *key, const secp256k1_scalar *nonce, const secp256k1_ge *pubnonce, secp256k1_schnorr_msghash hash, const unsigned char *msg32) { - secp256k1_gej Rj; - secp256k1_ge Ra; - unsigned char h32[32]; - secp256k1_scalar h, s; - int overflow; - secp256k1_scalar n; - - if (secp256k1_scalar_is_zero(key) || secp256k1_scalar_is_zero(nonce)) { - return 0; - } - n = *nonce; - - secp256k1_ecmult_gen(ctx, &Rj, &n); - if (pubnonce != NULL) { - secp256k1_gej_add_ge(&Rj, &Rj, pubnonce); - } - secp256k1_ge_set_gej(&Ra, &Rj); - secp256k1_fe_normalize(&Ra.y); - if (secp256k1_fe_is_odd(&Ra.y)) { - /* R's y coordinate is odd, which is not allowed (see rationale above). - Force it to be even by negating the nonce. Note that this even works - for multiparty signing, as the R point is known to all participants, - which can all decide to flip the sign in unison, resulting in the - overall R point to be negated too. */ - secp256k1_scalar_negate(&n, &n); - } - secp256k1_fe_normalize(&Ra.x); - secp256k1_fe_get_b32(sig64, &Ra.x); - hash(h32, sig64, msg32); - overflow = 0; - secp256k1_scalar_set_b32(&h, h32, &overflow); - if (overflow || secp256k1_scalar_is_zero(&h)) { - secp256k1_scalar_clear(&n); - return 0; - } - secp256k1_scalar_mul(&s, &h, key); - secp256k1_scalar_negate(&s, &s); - secp256k1_scalar_add(&s, &s, &n); - secp256k1_scalar_clear(&n); - secp256k1_scalar_get_b32(sig64 + 32, &s); - return 1; -} - -static int secp256k1_schnorr_sig_verify(const secp256k1_ecmult_context* ctx, const unsigned char *sig64, const secp256k1_ge *pubkey, secp256k1_schnorr_msghash hash, const unsigned char *msg32) { - secp256k1_gej Qj, Rj; - secp256k1_ge Ra; - secp256k1_fe Rx; - secp256k1_scalar h, s; - unsigned char hh[32]; - int overflow; - - if (secp256k1_ge_is_infinity(pubkey)) { - return 0; - } - hash(hh, sig64, msg32); - overflow = 0; - secp256k1_scalar_set_b32(&h, hh, &overflow); - if (overflow || secp256k1_scalar_is_zero(&h)) { - return 0; - } - overflow = 0; - secp256k1_scalar_set_b32(&s, sig64 + 32, &overflow); - if (overflow) { - return 0; - } - if (!secp256k1_fe_set_b32(&Rx, sig64)) { - return 0; - } - secp256k1_gej_set_ge(&Qj, pubkey); - secp256k1_ecmult(ctx, &Rj, &Qj, &h, &s); - if (secp256k1_gej_is_infinity(&Rj)) { - return 0; - } - secp256k1_ge_set_gej_var(&Ra, &Rj); - secp256k1_fe_normalize_var(&Ra.y); - if (secp256k1_fe_is_odd(&Ra.y)) { - return 0; - } - return secp256k1_fe_equal_var(&Rx, &Ra.x); -} - -static int secp256k1_schnorr_sig_recover(const secp256k1_ecmult_context* ctx, const unsigned char *sig64, secp256k1_ge *pubkey, secp256k1_schnorr_msghash hash, const unsigned char *msg32) { - secp256k1_gej Qj, Rj; - secp256k1_ge Ra; - secp256k1_fe Rx; - secp256k1_scalar h, s; - unsigned char hh[32]; - int overflow; - - hash(hh, sig64, msg32); - overflow = 0; - secp256k1_scalar_set_b32(&h, hh, &overflow); - if (overflow || secp256k1_scalar_is_zero(&h)) { - return 0; - } - overflow = 0; - secp256k1_scalar_set_b32(&s, sig64 + 32, &overflow); - if (overflow) { - return 0; - } - if (!secp256k1_fe_set_b32(&Rx, sig64)) { - return 0; - } - if (!secp256k1_ge_set_xo_var(&Ra, &Rx, 0)) { - return 0; - } - secp256k1_gej_set_ge(&Rj, &Ra); - secp256k1_scalar_inverse_var(&h, &h); - secp256k1_scalar_negate(&s, &s); - secp256k1_scalar_mul(&s, &s, &h); - secp256k1_ecmult(ctx, &Qj, &Rj, &h, &s); - if (secp256k1_gej_is_infinity(&Qj)) { - return 0; - } - secp256k1_ge_set_gej(pubkey, &Qj); - return 1; -} - -static int secp256k1_schnorr_sig_combine(unsigned char *sig64, size_t n, const unsigned char * const *sig64ins) { - secp256k1_scalar s = SECP256K1_SCALAR_CONST(0, 0, 0, 0, 0, 0, 0, 0); - size_t i; - for (i = 0; i < n; i++) { - secp256k1_scalar si; - int overflow; - secp256k1_scalar_set_b32(&si, sig64ins[i] + 32, &overflow); - if (overflow) { - return -1; - } - if (i) { - if (memcmp(sig64ins[i - 1], sig64ins[i], 32) != 0) { - return -1; - } - } - secp256k1_scalar_add(&s, &s, &si); - } - if (secp256k1_scalar_is_zero(&s)) { - return 0; - } - memcpy(sig64, sig64ins[0], 32); - secp256k1_scalar_get_b32(sig64 + 32, &s); - secp256k1_scalar_clear(&s); - return 1; -} - -#endif |