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field: Improve docs and tests of secp256k1_fe_set_b32

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This commit is contained in:
Tim Ruffing 2023-02-01 12:26:57 +01:00
parent ca92a35d01
commit e9fd3dff76
2 changed files with 67 additions and 1 deletions
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4
src/field.h
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@ -75,7 +75,9 @@ static int secp256k1_fe_equal_var(const secp256k1_fe *a, const secp256k1_fe *b);
/** Compare two field elements. Requires both inputs to be normalized */ /** Compare two field elements. Requires both inputs to be normalized */
static int secp256k1_fe_cmp_var(const secp256k1_fe *a, const secp256k1_fe *b); static int secp256k1_fe_cmp_var(const secp256k1_fe *a, const secp256k1_fe *b);
/** Set a field element equal to 32-byte big endian value. If successful, the resulting field element is normalized. */ /** Set a field element equal to 32-byte big endian value.
* Returns 1 if no overflow occurred, and then the output is normalized.
* Returns 0 if overflow occurred, and then the output is only weakly normalized. */
static int secp256k1_fe_set_b32(secp256k1_fe *r, const unsigned char *a); static int secp256k1_fe_set_b32(secp256k1_fe *r, const unsigned char *a);
/** Convert a field element to a 32-byte big endian value. Requires the input to be normalized */ /** Convert a field element to a 32-byte big endian value. Requires the input to be normalized */

64
src/tests.c
View File

@ -2961,6 +2961,69 @@ static void run_field_convert(void) {
CHECK(secp256k1_memcmp_var(&fes2, &fes, sizeof(fes)) == 0); CHECK(secp256k1_memcmp_var(&fes2, &fes, sizeof(fes)) == 0);
} }
static void run_field_be32_overflow(void) {
{
static const unsigned char zero_overflow[32] = {
0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
0xFF, 0xFF, 0xFF, 0xFE, 0xFF, 0xFF, 0xFC, 0x2F,
};
static const unsigned char zero[32] = { 0x00 };
unsigned char out[32];
secp256k1_fe fe;
CHECK(secp256k1_fe_set_b32(&fe, zero_overflow) == 0);
CHECK(secp256k1_fe_normalizes_to_zero(&fe) == 1);
secp256k1_fe_normalize(&fe);
CHECK(secp256k1_fe_is_zero(&fe) == 1);
secp256k1_fe_get_b32(out, &fe);
CHECK(secp256k1_memcmp_var(out, zero, 32) == 0);
}
{
static const unsigned char one_overflow[32] = {
0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
0xFF, 0xFF, 0xFF, 0xFE, 0xFF, 0xFF, 0xFC, 0x30,
};
static const unsigned char one[32] = {
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x01,
};
unsigned char out[32];
secp256k1_fe fe;
CHECK(secp256k1_fe_set_b32(&fe, one_overflow) == 0);
secp256k1_fe_normalize(&fe);
CHECK(secp256k1_fe_cmp_var(&fe, &secp256k1_fe_one) == 0);
secp256k1_fe_get_b32(out, &fe);
CHECK(secp256k1_memcmp_var(out, one, 32) == 0);
}
{
static const unsigned char ff_overflow[32] = {
0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
};
static const unsigned char ff[32] = {
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
0x00, 0x00, 0x00, 0x01, 0x00, 0x00, 0x03, 0xD0,
};
unsigned char out[32];
secp256k1_fe fe;
const secp256k1_fe fe_ff = SECP256K1_FE_CONST(0, 0, 0, 0, 0, 0, 0x01, 0x000003d0);
CHECK(secp256k1_fe_set_b32(&fe, ff_overflow) == 0);
secp256k1_fe_normalize(&fe);
CHECK(secp256k1_fe_cmp_var(&fe, &fe_ff) == 0);
secp256k1_fe_get_b32(out, &fe);
CHECK(secp256k1_memcmp_var(out, ff, 32) == 0);
}
}
/* Returns true if two field elements have the same representation. */ /* Returns true if two field elements have the same representation. */
static int fe_identical(const secp256k1_fe *a, const secp256k1_fe *b) { static int fe_identical(const secp256k1_fe *a, const secp256k1_fe *b) {
int ret = 1; int ret = 1;
@ -7515,6 +7578,7 @@ int main(int argc, char **argv) {
run_field_half(); run_field_half();
run_field_misc(); run_field_misc();
run_field_convert(); run_field_convert();
run_field_be32_overflow();
run_fe_mul(); run_fe_mul();
run_sqr(); run_sqr();
run_sqrt(); run_sqrt();