frost/secp256k1-zkp
3
0
Fork 0
Code Issues Pull Requests Actions Packages Projects Releases Wiki Activity

Improve comments/checks for fe_sqrt

Browse Source
This commit is contained in:
Pieter Wuille
2022-01-31 18:19:45 -05:00
parent 6ab35082ef
commit be82bd8e03
2 changed files with 23 additions and 8 deletions
Download Patch File Download Diff File Expand all files Collapse all files

17
src/field_impl.h
View File

@@ -55,9 +55,13 @@ static int secp256k1_fe_sqrt(secp256k1_fe *r, const secp256k1_fe *a) {
* itself always a square (a ** ((p+1)/4) is the square of a ** ((p+1)/8)).
*/
secp256k1_fe x2, x3, x6, x9, x11, x22, x44, x88, x176, x220, x223, t1;
int j;
int j, ret;
#ifdef VERIFY
VERIFY_CHECK(r != a);
secp256k1_fe_verify(a);
VERIFY_CHECK(a->magnitude <= 8);
#endif
/** The binary representation of (p + 1)/4 has 3 blocks of 1s, with lengths in
* { 2, 22, 223 }. Use an addition chain to calculate 2^n - 1 for each block:
@@ -141,7 +145,16 @@ static int secp256k1_fe_sqrt(secp256k1_fe *r, const secp256k1_fe *a) {
/* Check that a square root was actually calculated */
secp256k1_fe_sqr(&t1, r);
return secp256k1_fe_equal(&t1, a);
ret = secp256k1_fe_equal(&t1, a);
#ifdef VERIFY
if (!ret) {
secp256k1_fe_negate(&t1, &t1, 1);
secp256k1_fe_normalize_var(&t1);
VERIFY_CHECK(secp256k1_fe_equal_var(&t1, a));
}
#endif
return ret;
}
#ifndef VERIFY