From 9ab96f7b12c68af2be7f7fc5be555aa45e267fcc Mon Sep 17 00:00:00 2001 From: Jonas Nick Date: Wed, 27 Feb 2019 10:46:42 +0000 Subject: [PATCH] Use trivial algorithm in ecmult_multi if scratch space is small --- src/ecmult_impl.h | 10 ++++++---- src/tests.c | 42 +++++++++++++++++++++++++++++++----------- 2 files changed, 37 insertions(+), 15 deletions(-) diff --git a/src/ecmult_impl.h b/src/ecmult_impl.h index cbafd07..2587709 100644 --- a/src/ecmult_impl.h +++ b/src/ecmult_impl.h @@ -1152,16 +1152,18 @@ static int secp256k1_ecmult_multi_var(const secp256k1_ecmult_context *ctx, secp2 return secp256k1_ecmult_multi_simple_var(ctx, r, inp_g_sc, cb, cbdata, n); } - /* Compute the batch sizes for pippenger given a scratch space. If it's greater than a threshold - * use pippenger. Otherwise use strauss */ + /* Compute the batch sizes for Pippenger's algorithm given a scratch space. If it's greater than + * a threshold use Pippenger's algorithm. Otherwise use Strauss' algorithm. + * As a first step check if there's enough space for Pippenger's algo (which requires less space + * than Strauss' algo) and if not, use the simple algorithm. */ if (!secp256k1_ecmult_multi_batch_size_helper(&n_batches, &n_batch_points, secp256k1_pippenger_max_points(scratch), n)) { - return 0; + return secp256k1_ecmult_multi_simple_var(ctx, r, inp_g_sc, cb, cbdata, n); } if (n_batch_points >= ECMULT_PIPPENGER_THRESHOLD) { f = secp256k1_ecmult_pippenger_batch; } else { if (!secp256k1_ecmult_multi_batch_size_helper(&n_batches, &n_batch_points, secp256k1_strauss_max_points(scratch), n)) { - return 0; + return secp256k1_ecmult_multi_simple_var(ctx, r, inp_g_sc, cb, cbdata, n); } f = secp256k1_ecmult_strauss_batch; } diff --git a/src/tests.c b/src/tests.c index f1c4db9..7c24482 100644 --- a/src/tests.c +++ b/src/tests.c @@ -2572,7 +2572,6 @@ void test_ecmult_multi(secp256k1_scratch *scratch, secp256k1_ecmult_multi_func e secp256k1_gej r; secp256k1_gej r2; ecmult_multi_data data; - secp256k1_scratch *scratch_empty; data.sc = sc; data.pt = pt; @@ -2607,11 +2606,6 @@ void test_ecmult_multi(secp256k1_scratch *scratch, secp256k1_ecmult_multi_func e secp256k1_gej_add_var(&r, &r, &r2, NULL); CHECK(secp256k1_gej_is_infinity(&r)); - /* Try to multiply 1 point, but scratch space is empty */ - scratch_empty = secp256k1_scratch_create(&ctx->error_callback, 0); - CHECK(!ecmult_multi(&ctx->ecmult_ctx, scratch_empty, &r, &szero, ecmult_multi_callback, &data, 1)); - secp256k1_scratch_destroy(scratch_empty); - /* Try to multiply 1 point, but callback returns false */ CHECK(!ecmult_multi(&ctx->ecmult_ctx, scratch, &r, &szero, ecmult_multi_false_callback, &data, 1)); @@ -2809,6 +2803,24 @@ void test_ecmult_multi(secp256k1_scratch *scratch, secp256k1_ecmult_multi_func e } } +void test_ecmult_multi_batch_single(secp256k1_ecmult_multi_func ecmult_multi) { + secp256k1_scalar szero; + secp256k1_scalar sc[32]; + secp256k1_ge pt[32]; + secp256k1_gej r; + ecmult_multi_data data; + secp256k1_scratch *scratch_empty; + + data.sc = sc; + data.pt = pt; + secp256k1_scalar_set_int(&szero, 0); + + /* Try to multiply 1 point, but scratch space is empty.*/ + scratch_empty = secp256k1_scratch_create(&ctx->error_callback, 0); + CHECK(!ecmult_multi(&ctx->ecmult_ctx, scratch_empty, &r, &szero, ecmult_multi_callback, &data, 1)); + secp256k1_scratch_destroy(scratch_empty); +} + void test_secp256k1_pippenger_bucket_window_inv(void) { int i; @@ -2932,19 +2944,25 @@ void test_ecmult_multi_batching(void) { } data.sc = sc; data.pt = pt; + secp256k1_gej_neg(&r2, &r2); - /* Test with empty scratch space */ + /* Test with empty scratch space. It should compute the correct result using + * ecmult_mult_simple algorithm which doesn't require a scratch space. */ scratch = secp256k1_scratch_create(&ctx->error_callback, 0); - CHECK(!secp256k1_ecmult_multi_var(&ctx->ecmult_ctx, scratch, &r, &scG, ecmult_multi_callback, &data, 1)); + CHECK(secp256k1_ecmult_multi_var(&ctx->ecmult_ctx, scratch, &r, &scG, ecmult_multi_callback, &data, n_points)); + secp256k1_gej_add_var(&r, &r, &r2, NULL); + CHECK(secp256k1_gej_is_infinity(&r)); secp256k1_scratch_destroy(scratch); /* Test with space for 1 point in pippenger. That's not enough because - * ecmult_multi selects strauss which requires more memory. */ + * ecmult_multi selects strauss which requires more memory. It should + * therefore select the simple algorithm. */ scratch = secp256k1_scratch_create(&ctx->error_callback, secp256k1_pippenger_scratch_size(1, 1) + PIPPENGER_SCRATCH_OBJECTS*ALIGNMENT); - CHECK(!secp256k1_ecmult_multi_var(&ctx->ecmult_ctx, scratch, &r, &scG, ecmult_multi_callback, &data, 1)); + CHECK(secp256k1_ecmult_multi_var(&ctx->ecmult_ctx, scratch, &r, &scG, ecmult_multi_callback, &data, n_points)); + secp256k1_gej_add_var(&r, &r, &r2, NULL); + CHECK(secp256k1_gej_is_infinity(&r)); secp256k1_scratch_destroy(scratch); - secp256k1_gej_neg(&r2, &r2); for(i = 1; i <= n_points; i++) { if (i > ECMULT_PIPPENGER_THRESHOLD) { int bucket_window = secp256k1_pippenger_bucket_window(i); @@ -2972,7 +2990,9 @@ void run_ecmult_multi_tests(void) { test_ecmult_multi(scratch, secp256k1_ecmult_multi_var); test_ecmult_multi(NULL, secp256k1_ecmult_multi_var); test_ecmult_multi(scratch, secp256k1_ecmult_pippenger_batch_single); + test_ecmult_multi_batch_single(secp256k1_ecmult_pippenger_batch_single); test_ecmult_multi(scratch, secp256k1_ecmult_strauss_batch_single); + test_ecmult_multi_batch_single(secp256k1_ecmult_strauss_batch_single); secp256k1_scratch_destroy(scratch); /* Run test_ecmult_multi with space for exactly one point */