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using System;
using Org.BouncyCastle.Math;
using Org.BouncyCastle.Math.EC;
using Org.BouncyCastle.Security;
using Org.BouncyCastle.Crypto;
using Org.BouncyCastle.Crypto.Digests;
using Org.BouncyCastle.Crypto.Parameters;
namespace Org.BouncyCastle.Crypto.Signers
{
/**
* EC-DSA as described in X9.62
*/
public class ECDsaSigner
: IDsa
{
private ECKeyParameters key;
private SecureRandom random;
public string AlgorithmName
{
get { return "ECDSA"; }
}
public void Init(
bool forSigning,
ICipherParameters parameters)
{
if (forSigning)
{
if (parameters is ParametersWithRandom)
{
ParametersWithRandom rParam = (ParametersWithRandom) parameters;
this.random = rParam.Random;
parameters = rParam.Parameters;
}
else
{
this.random = new SecureRandom();
}
if (!(parameters is ECPrivateKeyParameters))
throw new InvalidKeyException("EC private key required for signing");
this.key = (ECPrivateKeyParameters) parameters;
}
else
{
if (!(parameters is ECPublicKeyParameters))
throw new InvalidKeyException("EC public key required for verification");
this.key = (ECPublicKeyParameters) parameters;
}
}
// 5.3 pg 28
/**
* Generate a signature for the given message using the key we were
* initialised with. For conventional DSA the message should be a SHA-1
* hash of the message of interest.
*
* @param message the message that will be verified later.
*/
public BigInteger[] GenerateSignature(
byte[] message)
{
BigInteger n = key.Parameters.N;
BigInteger e = calculateE(n, message);
BigInteger r = null;
BigInteger s = null;
// 5.3.2
do // Generate s
{
BigInteger k = null;
do // Generate r
{
do
{
k = new BigInteger(n.BitLength, random);
}
while (k.SignValue == 0 || k.CompareTo(n) >= 0);
ECPoint p = key.Parameters.G.Multiply(k);
// 5.3.3
BigInteger x = p.X.ToBigInteger();
r = x.Mod(n);
}
while (r.SignValue == 0);
BigInteger d = ((ECPrivateKeyParameters)key).D;
s = k.ModInverse(n).Multiply(e.Add(d.Multiply(r).Mod(n))).Mod(n);
}
while (s.SignValue == 0);
return new BigInteger[]{ r, s };
}
// 5.4 pg 29
/**
* return true if the value r and s represent a DSA signature for
* the passed in message (for standard DSA the message should be
* a SHA-1 hash of the real message to be verified).
*/
public bool VerifySignature(
byte[] message,
BigInteger r,
BigInteger s)
{
BigInteger n = key.Parameters.N;
// r and s should both in the range [1,n-1]
if (r.SignValue < 1 || s.SignValue < 1
|| r.CompareTo(n) >= 0 || s.CompareTo(n) >= 0)
{
return false;
}
BigInteger e = calculateE(n, message);
BigInteger c = s.ModInverse(n);
BigInteger u1 = e.Multiply(c).Mod(n);
BigInteger u2 = r.Multiply(c).Mod(n);
ECPoint G = key.Parameters.G;
ECPoint Q = ((ECPublicKeyParameters) key).Q;
ECPoint point = ECAlgorithms.SumOfTwoMultiplies(G, u1, Q, u2);
BigInteger v = point.X.ToBigInteger().Mod(n);
return v.Equals(r);
}
private BigInteger calculateE(
BigInteger n,
byte[] message)
{
int messageBitLength = message.Length * 8;
BigInteger trunc = new BigInteger(1, message);
if (n.BitLength < messageBitLength)
{
trunc = trunc.ShiftRight(messageBitLength - n.BitLength);
}
return trunc;
}
}
}
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