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using System;
using Org.BouncyCastle.Crypto.Parameters;
using Org.BouncyCastle.Math;
using Org.BouncyCastle.Security;
using Org.BouncyCastle.Utilities;
namespace Org.BouncyCastle.Crypto.Signers
{
/**
* The Digital Signature Algorithm - as described in "Handbook of Applied
* Cryptography", pages 452 - 453.
*/
public class DsaSigner
: IDsa
{
protected readonly IDsaKCalculator kCalculator;
protected DsaKeyParameters key = null;
protected SecureRandom random = null;
/**
* Default configuration, random K values.
*/
public DsaSigner()
{
this.kCalculator = new RandomDsaKCalculator();
}
/**
* Configuration with an alternate, possibly deterministic calculator of K.
*
* @param kCalculator a K value calculator.
*/
public DsaSigner(IDsaKCalculator kCalculator)
{
this.kCalculator = kCalculator;
}
public virtual string AlgorithmName
{
get { return "DSA"; }
}
public virtual void Init(bool forSigning, ICipherParameters parameters)
{
SecureRandom providedRandom = null;
if (forSigning)
{
if (parameters is ParametersWithRandom rParam)
{
providedRandom = rParam.Random;
parameters = rParam.Parameters;
}
if (!(parameters is DsaPrivateKeyParameters))
throw new InvalidKeyException("DSA private key required for signing");
this.key = (DsaPrivateKeyParameters)parameters;
}
else
{
if (!(parameters is DsaPublicKeyParameters))
throw new InvalidKeyException("DSA public key required for verification");
this.key = (DsaPublicKeyParameters)parameters;
}
this.random = InitSecureRandom(forSigning && !kCalculator.IsDeterministic, providedRandom);
}
public virtual BigInteger Order
{
get { return key.Parameters.Q; }
}
/**
* 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 virtual BigInteger[] GenerateSignature(byte[] message)
{
DsaParameters parameters = key.Parameters;
BigInteger q = parameters.Q;
BigInteger m = CalculateE(q, message);
BigInteger x = ((DsaPrivateKeyParameters)key).X;
if (kCalculator.IsDeterministic)
{
kCalculator.Init(q, x, message);
}
else
{
kCalculator.Init(q, random);
}
BigInteger k = kCalculator.NextK();
BigInteger r = parameters.G.ModPow(k, parameters.P).Mod(q);
k = BigIntegers.ModOddInverse(q, k).Multiply(m.Add(x.Multiply(r)));
BigInteger s = k.Mod(q);
return new BigInteger[]{ r, s };
}
/**
* 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 virtual bool VerifySignature(byte[] message, BigInteger r, BigInteger s)
{
DsaParameters parameters = key.Parameters;
BigInteger q = parameters.Q;
BigInteger m = CalculateE(q, message);
if (r.SignValue <= 0 || q.CompareTo(r) <= 0)
{
return false;
}
if (s.SignValue <= 0 || q.CompareTo(s) <= 0)
{
return false;
}
BigInteger w = BigIntegers.ModOddInverseVar(q, s);
BigInteger u1 = m.Multiply(w).Mod(q);
BigInteger u2 = r.Multiply(w).Mod(q);
BigInteger p = parameters.P;
u1 = parameters.G.ModPow(u1, p);
u2 = ((DsaPublicKeyParameters)key).Y.ModPow(u2, p);
BigInteger v = u1.Multiply(u2).Mod(p).Mod(q);
return v.Equals(r);
}
protected virtual BigInteger CalculateE(BigInteger n, byte[] message)
{
int length = System.Math.Min(message.Length, n.BitLength / 8);
return new BigInteger(1, message, 0, length);
}
protected virtual SecureRandom InitSecureRandom(bool needed, SecureRandom provided)
{
return !needed ? null : CryptoServicesRegistrar.GetSecureRandom(provided);
}
}
}
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