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fix ge_p3_is_point_at_infinity(), which is evaluating field elements that haven't been reduced by the field order

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This commit is contained in:
koe 2021-11-08 18:14:17 -06:00
parent eec3a6014c
commit c36ea26e5c
7 changed files with 111 additions and 11 deletions
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46
tests/crypto/crypto.cpp
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@ -32,6 +32,36 @@
#include "crypto-tests.h"
static void get_ge_p3_for_identity_test(const crypto::public_key &point, crypto::ge_p3 &result_out_p3)
{
// compute (K + K) - K - K to get a specific ge_p3 point representation of identity
crypto::ge_cached temp_cache;
crypto::ge_p1p1 temp_p1p1;
crypto::ge_frombytes_vartime(&result_out_p3, &point); // K
crypto::ge_p3_to_cached(&temp_cache, &result_out_p3);
crypto::ge_add(&temp_p1p1, &result_out_p3, &temp_cache); // K + K
crypto::ge_p1p1_to_p3(&result_out_p3, &temp_p1p1);
crypto::ge_sub(&temp_p1p1, &result_out_p3, &temp_cache); // (K + K) - K
crypto::ge_p1p1_to_p3(&result_out_p3, &temp_p1p1);
crypto::ge_sub(&temp_p1p1, &result_out_p3, &temp_cache); // ((K + K) - K) - K
crypto::ge_p1p1_to_p3(&result_out_p3, &temp_p1p1);
}
static int ge_p3_is_point_at_infinity_vartime_bad(const crypto::ge_p3 *p) {
// X = 0 and Y == Z
// bad: components of 'p' are not reduced mod q
int n;
for (n = 0; n < 10; ++n)
{
if (p->X[n] | p->T[n])
return 0;
if (p->Y[n] != p->Z[n])
return 0;
}
return 1;
}
bool check_scalar(const crypto::ec_scalar &scalar) {
return crypto::sc_check(crypto::operator &(scalar)) == 0;
}
@ -55,3 +85,19 @@ void hash_to_ec(const crypto::public_key &key, crypto::ec_point &res) {
crypto::hash_to_ec(key, tmp);
crypto::ge_p3_tobytes(crypto::operator &(res), &tmp);
}
bool check_ge_p3_identity_failure(const crypto::public_key &point)
{
crypto::ge_p3 ident_p3;
get_ge_p3_for_identity_test(point, ident_p3);
return ge_p3_is_point_at_infinity_vartime_bad(&ident_p3) == 1;
}
bool check_ge_p3_identity_success(const crypto::public_key &point)
{
crypto::ge_p3 ident_p3;
get_ge_p3_for_identity_test(point, ident_p3);
return crypto::ge_p3_is_point_at_infinity_vartime(&ident_p3) == 1;
}