diff options
Diffstat (limited to 'crypto')
| -rw-r--r-- | crypto/src/math/ec/ECFieldElement.cs | 25 |
1 files changed, 12 insertions, 13 deletions
diff --git a/crypto/src/math/ec/ECFieldElement.cs b/crypto/src/math/ec/ECFieldElement.cs index ddd66d2fa..6956baa04 100644 --- a/crypto/src/math/ec/ECFieldElement.cs +++ b/crypto/src/math/ec/ECFieldElement.cs @@ -285,7 +285,7 @@ namespace Org.BouncyCastle.Math.EC BigInteger y = ModMult(t2, t4); - return CheckSqrt(new FpFieldElement(q, r, ModHalf(y))); + return CheckSqrt(new FpFieldElement(q, r, ModHalfAbs(y))); } // q == 8m + 1 @@ -312,7 +312,7 @@ namespace Org.BouncyCastle.Math.EC P = new BigInteger(q.BitLength, rand); } while (P.CompareTo(q) >= 0 - || !(ModMult(P, P).Subtract(fourX).ModPow(legendreExponent, q).Equals(qMinusOne))); + || !ModReduce(P.Multiply(P).Subtract(fourX)).ModPow(legendreExponent, q).Equals(qMinusOne)); BigInteger[] result = LucasSequence(P, X, k); U = result[0]; @@ -320,17 +320,7 @@ namespace Org.BouncyCastle.Math.EC if (ModMult(V, V).Equals(fourX)) { - // Integer division by 2, mod q - if (V.TestBit(0)) - { - V = V.Add(q); - } - - V = V.ShiftRight(1); - - Debug.Assert(ModMult(V, V).Equals(X)); - - return new FpFieldElement(q, r, V); + return new FpFieldElement(q, r, ModHalfAbs(V)); } } while (U.Equals(BigInteger.One) || U.Equals(qMinusOne)); @@ -421,6 +411,15 @@ namespace Org.BouncyCastle.Math.EC { if (x.TestBit(0)) { + x = q.Add(x); + } + return x.ShiftRight(1); + } + + protected virtual BigInteger ModHalfAbs(BigInteger x) + { + if (x.TestBit(0)) + { x = q.Subtract(x); } return x.ShiftRight(1); |