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tests: Improve secp256k1_scalar_check_overflow tests (Issue #1812) #1819

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Merged
real-or-random merged 1 commit into from
Feb 4, 2026
+50 −9
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tests: Improve secp256k1_scalar_check_overflow tests (Issue #1812) #1819

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59 changes: 50 additions & 9 deletions src/tests.c
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Original file line number Diff line number Diff line change
Expand Up @@ -2193,8 +2193,58 @@ static void run_scalar_set_b32_seckey_tests(void) {
CHECK(secp256k1_scalar_set_b32_seckey(&s2, b32) == 0);
}

static void test_scalar_check_overflow(void) {
secp256k1_scalar s;
const secp256k1_scalar n_minus_1 = SECP256K1_SCALAR_CONST(
0xFFFFFFFFUL, 0xFFFFFFFFUL, 0xFFFFFFFFUL, 0xFFFFFFFEUL,
0xBAAEDCE6UL, 0xAF48A03BUL, 0xBFD25E8CUL, 0xD0364140UL
);
const secp256k1_scalar n = SECP256K1_SCALAR_CONST(
0xFFFFFFFFUL, 0xFFFFFFFFUL, 0xFFFFFFFFUL, 0xFFFFFFFEUL,
0xBAAEDCE6UL, 0xAF48A03BUL, 0xBFD25E8CUL, 0xD0364141UL
);
const secp256k1_scalar n_plus_1 = SECP256K1_SCALAR_CONST(
0xFFFFFFFFUL, 0xFFFFFFFFUL, 0xFFFFFFFFUL, 0xFFFFFFFEUL,
0xBAAEDCE6UL, 0xAF48A03BUL, 0xBFD25E8CUL, 0xD0364142UL
);
const secp256k1_scalar max = SECP256K1_SCALAR_CONST(
0xFFFFFFFFUL, 0xFFFFFFFFUL, 0xFFFFFFFFUL, 0xFFFFFFFFUL,
0xFFFFFFFFUL, 0xFFFFFFFFUL, 0xFFFFFFFFUL, 0xFFFFFFFFUL
);

int i;

secp256k1_scalar_set_int(&s, 0);
CHECK(secp256k1_scalar_check_overflow(&s) == 0);
CHECK(secp256k1_scalar_check_overflow(&n_minus_1) == 0);
CHECK(secp256k1_scalar_check_overflow(&n) == 1);
CHECK(secp256k1_scalar_check_overflow(&n_plus_1) == 1);
CHECK(secp256k1_scalar_check_overflow(&max) == 1);

for (i = 0; i < 2 * COUNT; i++) {
int expected_overflow;
int overflow = 0;
unsigned char b32[32];

testrand256(b32);

/* Force top bits to be 0xFF sometimes to ensure we hit overflows */
if (i % 2 == 0) {
memset(b32, 0xFF, 16);
}

expected_overflow = (secp256k1_memcmp_var(b32, secp256k1_group_order_bytes, 32) >= 0);

secp256k1_scalar_set_b32(&s, b32, &overflow);
CHECK(overflow == expected_overflow);
}
}

static void run_scalar_tests(void) {
int i;

test_scalar_check_overflow();
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@theStack theStack Feb 4, 2026 •
edited
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non-blocking nit: could add a newline before to separate the declaration block

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@therohityadav therohityadav Feb 4, 2026

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non-blocking nit: could add a newline before to separate the declaration block

I have added the newline to separate the declaration block.

Regarding the scalar constant deduplication: I am looking into doing that in a follow-up PR to keep this one focused.


for (i = 0; i < 128 * COUNT; i++) {
scalar_test();
}
Expand Down Expand Up @@ -2258,15 +2308,6 @@ static void run_scalar_tests(void) {
}
}

{
/* Does check_overflow check catch all ones? */
static const secp256k1_scalar overflowed = SECP256K1_SCALAR_CONST(
0xFFFFFFFFUL, 0xFFFFFFFFUL, 0xFFFFFFFFUL, 0xFFFFFFFFUL,
0xFFFFFFFFUL, 0xFFFFFFFFUL, 0xFFFFFFFFUL, 0xFFFFFFFFUL
);
CHECK(secp256k1_scalar_check_overflow(&overflowed));
}

{
/* Static test vectors.
* These were reduced from ~10^12 random vectors based on comparison-decision
Expand Down