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tests_exhaustive_impl.h
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tests_exhaustive_impl.h
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/***********************************************************************
* 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 "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 */