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Merge pull request #8052

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c36ea26 fix ge_p3_is_point_at_infinity(), which is evaluating field elements that haven't been reduced by the field order (koe)
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luigi1111 2022-03-02 18:52:51 -05:00
commit abae63c37d
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GPG key ID: F4ACA0183641E010
7 changed files with 111 additions and 11 deletions
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52
src/crypto/crypto-ops.c
View file

@ -3830,15 +3830,51 @@ int sc_isnonzero(const unsigned char *s) {
s[27] | s[28] | s[29] | s[30] | s[31]) - 1) >> 8) + 1;
}
int ge_p3_is_point_at_infinity(const ge_p3 *p) {
// X = 0 and Y == Z
int n;
for (n = 0; n < 10; ++n)
int ge_p3_is_point_at_infinity_vartime(const ge_p3 *p) {
// https://eprint.iacr.org/2008/522
// X == T == 0 and Y/Z == 1
// note: convert all pieces to canonical bytes in case rounding is required (i.e. an element is > q)
// note2: even though T = XY/Z is true for valid point representations (implying it isn't necessary to
// test T == 0), the input to this function might NOT be valid, so we must test T == 0
char result_X_bytes[32];
fe_tobytes((unsigned char*)&result_X_bytes, p->X);
// X != 0
for (int i = 0; i < 32; ++i)
{
if (p->X[n] | p->T[n])
return 0;
if (p->Y[n] != p->Z[n])
if (result_X_bytes[i])
return 0;
}
return 1;
char result_T_bytes[32];
fe_tobytes((unsigned char*)&result_T_bytes, p->T);
// T != 0
for (int i = 0; i < 32; ++i)
{
if (result_T_bytes[i])
return 0;
}
char result_Y_bytes[32];
char result_Z_bytes[32];
fe_tobytes((unsigned char*)&result_Y_bytes, p->Y);
fe_tobytes((unsigned char*)&result_Z_bytes, p->Z);
// Y != Z
for (int i = 0; i < 32; ++i)
{
if (result_Y_bytes[i] != result_Z_bytes[i])
return 0;
}
// is Y nonzero? then Y/Z == 1
for (int i = 0; i < 32; ++i)
{
if (result_Y_bytes[i] != 0)
return 1;
}
// Y/Z = 0/0
return 0;
}

2
src/crypto/crypto-ops.h
View file

@ -162,4 +162,4 @@ void fe_add(fe h, const fe f, const fe g);
void fe_tobytes(unsigned char *, const fe);
void fe_invert(fe out, const fe z);
int ge_p3_is_point_at_infinity(const ge_p3 *p);
int ge_p3_is_point_at_infinity_vartime(const ge_p3 *p);

4
src/ringct/multiexp.cc
View file

@ -235,7 +235,7 @@ rct::key bos_coster_heap_conv_robust(std::vector<MultiexpData> data)
heap.reserve(points);
for (size_t n = 0; n < points; ++n)
{
if (!(data[n].scalar == rct::zero()) && !ge_p3_is_point_at_infinity(&data[n].point))
if (!(data[n].scalar == rct::zero()) && !ge_p3_is_point_at_infinity_vartime(&data[n].point))
heap.push_back(n);
}
points = heap.size();
@ -457,7 +457,7 @@ rct::key straus(const std::vector<MultiexpData> &data, const std::shared_ptr<str
MULTIEXP_PERF(PERF_TIMER_START_UNIT(skip, 1000000));
std::vector<uint8_t> skip(data.size());
for (size_t i = 0; i < data.size(); ++i)
skip[i] = data[i].scalar == rct::zero() || ge_p3_is_point_at_infinity(&data[i].point);
skip[i] = data[i].scalar == rct::zero() || ge_p3_is_point_at_infinity_vartime(&data[i].point);
MULTIEXP_PERF(PERF_TIMER_STOP(skip));
#endif