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crypto::point_t::is_zero() now treats non-points (0, 0, 0, ?) or incorrectly encoded points (0, x, x, !0) as not an identity and thus returns false + test

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sowle 2023-12-04 22:33:38 +01:00
parent 10cce8002f
commit 30299724fd
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GPG key ID: C07A24B2D89D49FC
2 changed files with 37 additions and 2 deletions
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8
src/crypto/crypto-sugar.h
View file

@ -612,9 +612,13 @@ namespace crypto
bool is_zero() const
{
// (0, 1) ~ (0, z, z, 0)
// (0, 1) ~ (0, z, z, 0) for any non-zero z https://www.rfc-editor.org/rfc/rfc8032#page-17
if (fe_isnonzero(m_p3.X) != 0)
return false;
return false; // x != 0
if (fe_isnonzero(m_p3.Z) == 0)
return false; // z == 0
if (fe_isnonzero(m_p3.T) != 0)
return false; // t != 0
fe y_minus_z;
fe_sub(y_minus_z, m_p3.Y, m_p3.Z);
return fe_isnonzero(y_minus_z) == 0;

31
tests/functional_tests/crypto_tests.cpp
View file

@ -1466,6 +1466,37 @@ TEST(crypto, point_is_zero)
ASSERT_TRUE(p.is_zero());
memset(&p.m_p3, 0, sizeof p.m_p3);
memcpy(&p.m_p3.Y, f_x, sizeof p.m_p3.Y);
memcpy(&p.m_p3.Z, f_x, sizeof p.m_p3.Z);
memcpy(&p.m_p3.T, fancy_p, sizeof p.m_p3.T);
// {0, x, x, P} == {0, 1} (still the identity point)
ASSERT_TRUE(p.is_zero());
//
// negative tests
//
memset(&p.m_p3, 0, sizeof p.m_p3);
// {0, 0, 0, 0} is not a point at all
ASSERT_FALSE(p.is_zero());
memset(&p.m_p3, 0, sizeof p.m_p3);
memcpy(&p.m_p3.Y, f_x, sizeof p.m_p3.Y);
memcpy(&p.m_p3.Z, f_x, sizeof p.m_p3.Z);
memcpy(&p.m_p3.T, fancy_p_plus_1, sizeof p.m_p3.T);
// {0, x, x, !0} is not a valid point (incorrect non-zero T)
ASSERT_FALSE(p.is_zero());
memcpy(&p.m_p3.T, f_x, sizeof p.m_p3.T);
// {0, x, x, x}, while x != 0 is still incorrect point representation
ASSERT_FALSE(p.is_zero());
return true;
}