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| author | Peter Dettman <peter.dettman@bouncycastle.org> | 2014-01-28 15:30:24 +0700 |
|---|---|---|
| committer | Peter Dettman <peter.dettman@bouncycastle.org> | 2014-01-28 15:30:24 +0700 |
| commit | 09e818fcc7677148e507409559bcae743d170d57 (patch) | |
| tree | f826cdb94aedb6422b4d5c54f7ac86c69516e0c8 /crypto/src/math/ec | |
| parent | Implement multi-squaring in-place and use for F2m sqrt() (diff) | |
| download | BouncyCastle.NET-ed25519-09e818fcc7677148e507409559bcae743d170d57.tar.xz | |
Avoid division when decompressing a lambda-projective point
Diffstat (limited to 'crypto/src/math/ec')
| -rw-r--r-- | crypto/src/math/ec/ECCurve.cs | 14 |
1 files changed, 5 insertions, 9 deletions
diff --git a/crypto/src/math/ec/ECCurve.cs b/crypto/src/math/ec/ECCurve.cs index ee3bcc69b..0c150848a 100644 --- a/crypto/src/math/ec/ECCurve.cs +++ b/crypto/src/math/ec/ECCurve.cs @@ -871,19 +871,16 @@ namespace Org.BouncyCastle.Math.EC return si; } - protected override ECPoint DecompressPoint( - int yTilde, - BigInteger X1) + protected override ECPoint DecompressPoint(int yTilde, BigInteger X1) { - ECFieldElement xp = FromBigInteger(X1); - ECFieldElement yp; + ECFieldElement xp = FromBigInteger(X1), yp; if (xp.IsZero) { yp = m_b.Sqrt(); } else { - ECFieldElement beta = xp.Add(m_a).Add(m_b.Multiply(xp.Square().Invert())); + ECFieldElement beta = xp.Square().Invert().Multiply(B).Add(A).Add(xp); ECFieldElement z = SolveQuadradicEquation(beta); if (z == null) @@ -894,18 +891,17 @@ namespace Org.BouncyCastle.Math.EC z = z.AddOne(); } - yp = xp.Multiply(z); - switch (this.CoordinateSystem) { case COORD_LAMBDA_AFFINE: case COORD_LAMBDA_PROJECTIVE: { - yp = yp.Divide(xp).Add(xp); + yp = z.Add(xp); break; } default: { + yp = z.Multiply(xp); break; } } |