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Merge bitcoin-core/secp256k1#1172: benchmarks: fix bench_scalar_split

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eb6bebaee3947f8bca46816fa6bf6182085f1b56 scalar: restrict split_lambda args, improve doc and VERIFY_CHECKs (Jonas Nick)
7f49aa7f2dca595ac8b58d0268dc46a9dfff1e38 ci: add test job with -DVERIFY (Jonas Nick)
620ba3d74bed3095cec7cd8877c8ce14cbf5e329 benchmarks: fix bench_scalar_split (Jonas Nick)

Pull request description:

  scalar_split_lambda requires that the input pointer is different to both output
  pointers. Without this fix, the internal benchmarks crash when compiled with
  -DVERIFY.

  This was introduced in commit 362bb25608 (which
  requires configuring with --enable-endomorphism to exhibit the crash).

  I tested that the new CI job would have caught this bug.

ACKs for top commit:
  sipa:
    utACK eb6bebaee3947f8bca46816fa6bf6182085f1b56
  real-or-random:
    utACK eb6bebaee3947f8bca46816fa6bf6182085f1b56

Tree-SHA512: c810545aefb01561ddb77b53618fa7acbb156ec13ab809c00523d4758492cafab1dfa01b6ebfb6195a3803bb49b16e63e8b0efcd1abb76ecefdb0476c3e483a3
This commit is contained in:
Pieter Wuille 2023-01-19 17:40:31 -05:00
commit 2b77240b3b
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GPG Key ID: BF2978B068054311
4 changed files with 14 additions and 7 deletions
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1
.cirrus.yml
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@ -81,6 +81,7 @@ task:
- env: {WIDEMUL: int128, ECDH: yes, SCHNORRSIG: yes}
- env: {WIDEMUL: int128, ASM: x86_64}
- env: { RECOVERY: yes, SCHNORRSIG: yes}
- env: {CTIMETESTS: no, RECOVERY: yes, ECDH: yes, SCHNORRSIG: yes, CPPFLAGS: -DVERIFY}
- env: {BUILD: distcheck, WITH_VALGRIND: no, CTIMETESTS: no, BENCH: no}
- env: {CPPFLAGS: -DDETERMINISTIC}
- env: {CFLAGS: -O0, CTIMETESTS: no}

5
src/bench_internal.c
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@ -110,10 +110,11 @@ static void bench_scalar_mul(void* arg, int iters) {
static void bench_scalar_split(void* arg, int iters) {
int i, j = 0;
bench_inv *data = (bench_inv*)arg;
secp256k1_scalar tmp;
for (i = 0; i < iters; i++) {
secp256k1_scalar_split_lambda(&data->scalar[0], &data->scalar[1], &data->scalar[0]);
j += secp256k1_scalar_add(&data->scalar[0], &data->scalar[0], &data->scalar[1]);
secp256k1_scalar_split_lambda(&tmp, &data->scalar[1], &data->scalar[0]);
j += secp256k1_scalar_add(&data->scalar[0], &tmp, &data->scalar[1]);
}
CHECK(j <= iters);
}

7
src/scalar.h
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@ -88,9 +88,10 @@ static int secp256k1_scalar_eq(const secp256k1_scalar *a, const secp256k1_scalar
/** Find r1 and r2 such that r1+r2*2^128 = k. */
static void secp256k1_scalar_split_128(secp256k1_scalar *r1, secp256k1_scalar *r2, const secp256k1_scalar *k);
/** Find r1 and r2 such that r1+r2*lambda = k,
* where r1 and r2 or their negations are maximum 128 bits long (see secp256k1_ge_mul_lambda). */
static void secp256k1_scalar_split_lambda(secp256k1_scalar *r1, secp256k1_scalar *r2, const secp256k1_scalar *k);
/** Find r1 and r2 such that r1+r2*lambda = k, where r1 and r2 or their
* negations are maximum 128 bits long (see secp256k1_ge_mul_lambda). It is
* required that r1, r2, and k all point to different objects. */
static void secp256k1_scalar_split_lambda(secp256k1_scalar * SECP256K1_RESTRICT r1, secp256k1_scalar * SECP256K1_RESTRICT r2, const secp256k1_scalar * SECP256K1_RESTRICT k);
/** Multiply a and b (without taking the modulus!), divide by 2**shift, and round to the nearest integer. Shift must be at least 256. */
static void secp256k1_scalar_mul_shift_var(secp256k1_scalar *r, const secp256k1_scalar *a, const secp256k1_scalar *b, unsigned int shift);

8
src/scalar_impl.h
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@ -52,7 +52,10 @@ static int secp256k1_scalar_set_b32_seckey(secp256k1_scalar *r, const unsigned c
* nontrivial to get full test coverage for the exhaustive tests. We therefore
* (arbitrarily) set r2 = k + 5 (mod n) and r1 = k - r2 * lambda (mod n).
*/
static void secp256k1_scalar_split_lambda(secp256k1_scalar *r1, secp256k1_scalar *r2, const secp256k1_scalar *k) {
static void secp256k1_scalar_split_lambda(secp256k1_scalar * SECP256K1_RESTRICT r1, secp256k1_scalar * SECP256K1_RESTRICT r2, const secp256k1_scalar * SECP256K1_RESTRICT k) {
VERIFY_CHECK(r1 != k);
VERIFY_CHECK(r2 != k);
VERIFY_CHECK(r1 != r2);
*r2 = (*k + 5) % EXHAUSTIVE_TEST_ORDER;
*r1 = (*k + (EXHAUSTIVE_TEST_ORDER - *r2) * EXHAUSTIVE_TEST_LAMBDA) % EXHAUSTIVE_TEST_ORDER;
}
@ -119,7 +122,7 @@ static void secp256k1_scalar_split_lambda_verify(const secp256k1_scalar *r1, con
*
* See proof below.
*/
static void secp256k1_scalar_split_lambda(secp256k1_scalar *r1, secp256k1_scalar *r2, const secp256k1_scalar *k) {
static void secp256k1_scalar_split_lambda(secp256k1_scalar * SECP256K1_RESTRICT r1, secp256k1_scalar * SECP256K1_RESTRICT r2, const secp256k1_scalar * SECP256K1_RESTRICT k) {
secp256k1_scalar c1, c2;
static const secp256k1_scalar minus_b1 = SECP256K1_SCALAR_CONST(
0x00000000UL, 0x00000000UL, 0x00000000UL, 0x00000000UL,
@ -139,6 +142,7 @@ static void secp256k1_scalar_split_lambda(secp256k1_scalar *r1, secp256k1_scalar
);
VERIFY_CHECK(r1 != k);
VERIFY_CHECK(r2 != k);
VERIFY_CHECK(r1 != r2);
/* these _var calls are constant time since the shift amount is constant */
secp256k1_scalar_mul_shift_var(&c1, k, &g1, 384);
secp256k1_scalar_mul_shift_var(&c2, k, &g2, 384);