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| author | Peter Dettman <peter.dettman@bouncycastle.org> | 2014-01-26 11:30:50 +0700 |
|---|---|---|
| committer | Peter Dettman <peter.dettman@bouncycastle.org> | 2014-01-26 11:30:50 +0700 |
| commit | 0ad06688318b3220928f84d48c2c1572215c2f6f (patch) | |
| tree | 85edb76f94d9be32ae40aee78c19bf8fbf2989fb | |
| parent | Increase number of rounds (diff) | |
| download | BouncyCastle.NET-ed25519-0ad06688318b3220928f84d48c2c1572215c2f6f.tar.xz | |
Make Barrett reduction available for more prime moduli
| -rw-r--r-- | crypto/src/math/ec/ECFieldElement.cs | 18 |
1 files changed, 6 insertions, 12 deletions
diff --git a/crypto/src/math/ec/ECFieldElement.cs b/crypto/src/math/ec/ECFieldElement.cs index ac9c62807..838053827 100644 --- a/crypto/src/math/ec/ECFieldElement.cs +++ b/crypto/src/math/ec/ECFieldElement.cs @@ -78,21 +78,14 @@ namespace Org.BouncyCastle.Math.EC internal static BigInteger CalculateResidue(BigInteger p) { int bitLength = p.BitLength; - if (bitLength > 128) - //if (bitLength > 64) + if (bitLength >= 96) { - /* - * NOTE: Due to poor performance of BigInteger.Mod in C#, the residue-based reduction is - * currently faster even for e.g. P-256, where the prime has 32 leading 1 bits. - */ BigInteger firstWord = p.ShiftRight(bitLength - 64); if (firstWord.LongValue == -1L) - //BigInteger firstWord = p.ShiftRight(bitLength - 32); - //if (firstWord.IntValue == -1) { return BigInteger.One.ShiftLeft(bitLength).Subtract(p); } - if ((bitLength & 31) == 0) + if ((bitLength & 7) == 0) { return BigInteger.One.ShiftLeft(bitLength << 1).Divide(p).Negate(); } @@ -382,11 +375,12 @@ namespace Org.BouncyCastle.Math.EC } else { + int d = ((qLen - 1) & 31) + 1; BigInteger mu = r.Negate(); - BigInteger u = mu.Multiply(x.ShiftRight(qLen - 32)); - BigInteger quot = u.ShiftRight(qLen + 32); + BigInteger u = mu.Multiply(x.ShiftRight(qLen - d)); + BigInteger quot = u.ShiftRight(qLen + d); BigInteger v = quot.Multiply(q); - BigInteger bk1 = BigInteger.One.ShiftLeft(qLen + 32); + BigInteger bk1 = BigInteger.One.ShiftLeft(qLen + d); v = v.Remainder(bk1); x = x.Remainder(bk1); x = x.Subtract(v); |