/*********************************************************************** * Copyright (c) 2016 Andrew Poelstra * * Distributed under the MIT software license, see the accompanying * * file COPYING or https://www.opensource.org/licenses/mit-license.php.* ***********************************************************************/ #ifndef SECP256K1_MODULE_RECOVERY_EXHAUSTIVE_TESTS_H #define SECP256K1_MODULE_RECOVERY_EXHAUSTIVE_TESTS_H #include "src/modules/recovery/main_impl.h" #include "include/secp256k1_recovery.h" void test_exhaustive_recovery_sign(const secp256k1_context *ctx, const secp256k1_ge *group) { int i, j, k; uint64_t iter = 0; /* Loop */ for (i = 1; i < EXHAUSTIVE_TEST_ORDER; i++) { /* message */ for (j = 1; j < EXHAUSTIVE_TEST_ORDER; j++) { /* key */ if (skip_section(&iter)) continue; for (k = 1; k < EXHAUSTIVE_TEST_ORDER; k++) { /* nonce */ const int starting_k = k; secp256k1_fe r_dot_y_normalized; secp256k1_ecdsa_recoverable_signature rsig; secp256k1_ecdsa_signature sig; secp256k1_scalar sk, msg, r, s, expected_r; unsigned char sk32[32], msg32[32]; int expected_recid; int recid; int overflow; secp256k1_scalar_set_int(&msg, i); secp256k1_scalar_set_int(&sk, j); secp256k1_scalar_get_b32(sk32, &sk); secp256k1_scalar_get_b32(msg32, &msg); secp256k1_ecdsa_sign_recoverable(ctx, &rsig, msg32, sk32, secp256k1_nonce_function_smallint, &k); /* Check directly */ secp256k1_ecdsa_recoverable_signature_load(ctx, &r, &s, &recid, &rsig); r_from_k(&expected_r, group, k, &overflow); CHECK(r == expected_r); CHECK((k * s) % EXHAUSTIVE_TEST_ORDER == (i + r * j) % EXHAUSTIVE_TEST_ORDER || (k * (EXHAUSTIVE_TEST_ORDER - s)) % EXHAUSTIVE_TEST_ORDER == (i + r * j) % EXHAUSTIVE_TEST_ORDER); /* The recid's second bit is for conveying overflow (R.x value >= group order). * In the actual secp256k1 this is an astronomically unlikely event, but in the * small group used here, it will be the case for all points except the ones where * R.x=1 (which the group is specifically selected to have). * Note that this isn't actually useful; full recovery would need to convey * floor(R.x / group_order), but only one bit is used as that is sufficient * in the real group. */ expected_recid = overflow ? 2 : 0; r_dot_y_normalized = group[k].y; secp256k1_fe_normalize(&r_dot_y_normalized); /* Also the recovery id is flipped depending if we hit the low-s branch */ if ((k * s) % EXHAUSTIVE_TEST_ORDER == (i + r * j) % EXHAUSTIVE_TEST_ORDER) { expected_recid |= secp256k1_fe_is_odd(&r_dot_y_normalized); } else { expected_recid |= !secp256k1_fe_is_odd(&r_dot_y_normalized); } CHECK(recid == expected_recid); /* Convert to a standard sig then check */ secp256k1_ecdsa_recoverable_signature_convert(ctx, &sig, &rsig); secp256k1_ecdsa_signature_load(ctx, &r, &s, &sig); /* Note that we compute expected_r *after* signing -- this is important * because our nonce-computing function function might change k during * signing. */ r_from_k(&expected_r, group, k, NULL); CHECK(r == expected_r); CHECK((k * s) % EXHAUSTIVE_TEST_ORDER == (i + r * j) % EXHAUSTIVE_TEST_ORDER || (k * (EXHAUSTIVE_TEST_ORDER - s)) % EXHAUSTIVE_TEST_ORDER == (i + r * j) % EXHAUSTIVE_TEST_ORDER); /* Overflow means we've tried every possible nonce */ if (k < starting_k) { break; } } } } } void test_exhaustive_recovery_verify(const secp256k1_context *ctx, const secp256k1_ge *group) { /* This is essentially a copy of test_exhaustive_verify, with recovery added */ int s, r, msg, key; uint64_t iter = 0; for (s = 1; s < EXHAUSTIVE_TEST_ORDER; s++) { for (r = 1; r < EXHAUSTIVE_TEST_ORDER; r++) { for (msg = 1; msg < EXHAUSTIVE_TEST_ORDER; msg++) { for (key = 1; key < EXHAUSTIVE_TEST_ORDER; key++) { secp256k1_ge nonconst_ge; secp256k1_ecdsa_recoverable_signature rsig; secp256k1_ecdsa_signature sig; secp256k1_pubkey pk; secp256k1_scalar sk_s, msg_s, r_s, s_s; secp256k1_scalar s_times_k_s, msg_plus_r_times_sk_s; int recid = 0; int k, should_verify; unsigned char msg32[32]; if (skip_section(&iter)) continue; secp256k1_scalar_set_int(&s_s, s); secp256k1_scalar_set_int(&r_s, r); secp256k1_scalar_set_int(&msg_s, msg); secp256k1_scalar_set_int(&sk_s, key); secp256k1_scalar_get_b32(msg32, &msg_s); /* Verify by hand */ /* Run through every k value that gives us this r and check that *one* works. * Note there could be none, there could be multiple, ECDSA is weird. */ should_verify = 0; for (k = 0; k < EXHAUSTIVE_TEST_ORDER; k++) { secp256k1_scalar check_x_s; r_from_k(&check_x_s, group, k, NULL); if (r_s == check_x_s) { secp256k1_scalar_set_int(&s_times_k_s, k); secp256k1_scalar_mul(&s_times_k_s, &s_times_k_s, &s_s); secp256k1_scalar_mul(&msg_plus_r_times_sk_s, &r_s, &sk_s); secp256k1_scalar_add(&msg_plus_r_times_sk_s, &msg_plus_r_times_sk_s, &msg_s); should_verify |= secp256k1_scalar_eq(&s_times_k_s, &msg_plus_r_times_sk_s); } } /* nb we have a "high s" rule */ should_verify &= !secp256k1_scalar_is_high(&s_s); /* We would like to try recovering the pubkey and checking that it matches, * but pubkey recovery is impossible in the exhaustive tests (the reason * being that there are 12 nonzero r values, 12 nonzero points, and no * overlap between the sets, so there are no valid signatures). */ /* Verify by converting to a standard signature and calling verify */ secp256k1_ecdsa_recoverable_signature_save(&rsig, &r_s, &s_s, recid); secp256k1_ecdsa_recoverable_signature_convert(ctx, &sig, &rsig); memcpy(&nonconst_ge, &group[sk_s], sizeof(nonconst_ge)); secp256k1_pubkey_save(&pk, &nonconst_ge); CHECK(should_verify == secp256k1_ecdsa_verify(ctx, &sig, msg32, &pk)); } } } } } static void test_exhaustive_recovery(const secp256k1_context *ctx, const secp256k1_ge *group) { test_exhaustive_recovery_sign(ctx, group); test_exhaustive_recovery_verify(ctx, group); } #endif /* SECP256K1_MODULE_RECOVERY_EXHAUSTIVE_TESTS_H */