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Merge #1371: Add exhaustive tests for ellswift (with create+decode ro…
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…undtrip)

2792119 Add exhaustive test for ellswift (create+decode roundtrip) (Sebastian Falbesoner)

Pull request description:

  This PR adds the basic structure for ellswift exhaustive tests. Right now only a `secp256k1_ellswift_create` + `secp256k1_ellswift_decode` indirect roundtrip (exhaustive loop scalar -> ellswift pubkey -> decoded pubkey -> decoded group element, compared with exhaustive precomputed group element) is included.

  The exhaustive tests passes locally with all currently supported orders (n=13 [default] and n=199). Note that for n=7, the test is skipped, as the used curve in this case is even-ordered and ellswift only supports odd-ordered curves.

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Tree-SHA512: c51d3d99e9839793b3c15d75b9a29f01080db160ab8819973abd877288f9f0af972ea4264290220ab1cd035fdebcfac7767436aa39154d924ef0bf6a5733a55d
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real-or-random committed Jul 5, 2023
2 parents 332af31 + 2792119 commit afd7eb4
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1 change: 1 addition & 0 deletions src/modules/ellswift/Makefile.am.include
Original file line number Diff line number Diff line change
Expand Up @@ -2,3 +2,4 @@ include_HEADERS += include/secp256k1_ellswift.h
noinst_HEADERS += src/modules/ellswift/bench_impl.h
noinst_HEADERS += src/modules/ellswift/main_impl.h
noinst_HEADERS += src/modules/ellswift/tests_impl.h
noinst_HEADERS += src/modules/ellswift/tests_exhaustive_impl.h
39 changes: 39 additions & 0 deletions src/modules/ellswift/tests_exhaustive_impl.h
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@@ -0,0 +1,39 @@
/***********************************************************************
* Distributed under the MIT software license, see the accompanying *
* file COPYING or https://www.opensource.org/licenses/mit-license.php.*
***********************************************************************/

#ifndef SECP256K1_MODULE_ELLSWIFT_TESTS_EXHAUSTIVE_H
#define SECP256K1_MODULE_ELLSWIFT_TESTS_EXHAUSTIVE_H

#include "../../../include/secp256k1_ellswift.h"
#include "main_impl.h"

static void test_exhaustive_ellswift(const secp256k1_context *ctx, const secp256k1_ge *group) {
int i;

/* Note that SwiftEC/ElligatorSwift are inherently curve operations, not
* group operations, and this test only checks the curve points which are in
* a tiny subgroup. In that sense it can't be really seen as exhaustive as
* it doesn't (and for computational reasons obviously cannot) test the
* entire domain ellswift operates under. */
for (i = 1; i < EXHAUSTIVE_TEST_ORDER; i++) {
secp256k1_scalar scalar_i;
unsigned char sec32[32];
unsigned char ell64[64];
secp256k1_pubkey pub_decoded;
secp256k1_ge ge_decoded;

/* Construct ellswift pubkey from exhaustive loop scalar i. */
secp256k1_scalar_set_int(&scalar_i, i);
secp256k1_scalar_get_b32(sec32, &scalar_i);
CHECK(secp256k1_ellswift_create(ctx, ell64, sec32, NULL));

/* Decode ellswift pubkey and check that it matches the precomputed group element. */
secp256k1_ellswift_decode(ctx, &pub_decoded, ell64);
secp256k1_pubkey_load(ctx, &ge_decoded, &pub_decoded);
ge_equals_ge(&ge_decoded, &group[i]);
}
}

#endif
16 changes: 16 additions & 0 deletions src/tests_exhaustive.c
Original file line number Diff line number Diff line change
Expand Up @@ -13,6 +13,9 @@
#define EXHAUSTIVE_TEST_ORDER 13
#endif

/* These values of B are all values in [1, 8] that result in a curve with even order. */
#define EXHAUSTIVE_TEST_CURVE_HAS_EVEN_ORDER (SECP256K1_B == 1 || SECP256K1_B == 6 || SECP256K1_B == 8)

#ifdef USE_EXTERNAL_DEFAULT_CALLBACKS
#pragma message("Ignoring USE_EXTERNAL_CALLBACKS in exhaustive_tests.")
#undef USE_EXTERNAL_DEFAULT_CALLBACKS
Expand Down Expand Up @@ -395,6 +398,10 @@ static void test_exhaustive_sign(const secp256k1_context *ctx, const secp256k1_g
#include "modules/schnorrsig/tests_exhaustive_impl.h"
#endif

#ifdef ENABLE_MODULE_ELLSWIFT
#include "modules/ellswift/tests_exhaustive_impl.h"
#endif

int main(int argc, char** argv) {
int i;
secp256k1_gej groupj[EXHAUSTIVE_TEST_ORDER];
Expand Down Expand Up @@ -490,6 +497,15 @@ int main(int argc, char** argv) {
#ifdef ENABLE_MODULE_SCHNORRSIG
test_exhaustive_schnorrsig(ctx);
#endif
#ifdef ENABLE_MODULE_ELLSWIFT
/* The ellswift algorithm does have additional edge cases when operating on
* curves of even order, which are not included in the code as secp256k1 is
* of odd order. Skip the ellswift tests if the used exhaustive tests curve
* is even-ordered accordingly. */
#if !EXHAUSTIVE_TEST_CURVE_HAS_EVEN_ORDER
test_exhaustive_ellswift(ctx, group);
#endif
#endif

secp256k1_context_destroy(ctx);
}
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