DHAgreement
using Org.BouncyCastle.Crypto.Generators;
using Org.BouncyCastle.Crypto.Parameters;
using Org.BouncyCastle.Math;
using Org.BouncyCastle.Security;
using System;
namespace Org.BouncyCastle.Crypto.Agreement
{
public class DHAgreement
{
private DHPrivateKeyParameters key;
private DHParameters dhParams;
private BigInteger privateValue;
private SecureRandom random;
public void Init(ICipherParameters parameters)
{
ParametersWithRandom parametersWithRandom = parameters as ParametersWithRandom;
AsymmetricKeyParameter asymmetricKeyParameter;
if (parametersWithRandom != null) {
random = parametersWithRandom.Random;
asymmetricKeyParameter = (AsymmetricKeyParameter)parametersWithRandom.Parameters;
} else {
random = CryptoServicesRegistrar.GetSecureRandom();
asymmetricKeyParameter = (AsymmetricKeyParameter)parameters;
}
DHPrivateKeyParameters dHPrivateKeyParameters = asymmetricKeyParameter as DHPrivateKeyParameters;
if (dHPrivateKeyParameters == null)
throw new ArgumentException("DHEngine expects DHPrivateKeyParameters");
key = dHPrivateKeyParameters;
dhParams = dHPrivateKeyParameters.Parameters;
}
public BigInteger CalculateMessage()
{
DHKeyPairGenerator dHKeyPairGenerator = new DHKeyPairGenerator();
dHKeyPairGenerator.Init(new DHKeyGenerationParameters(random, dhParams));
AsymmetricCipherKeyPair asymmetricCipherKeyPair = dHKeyPairGenerator.GenerateKeyPair();
privateValue = ((DHPrivateKeyParameters)asymmetricCipherKeyPair.Private).X;
return ((DHPublicKeyParameters)asymmetricCipherKeyPair.Public).Y;
}
public BigInteger CalculateAgreement(DHPublicKeyParameters pub, BigInteger message)
{
if (pub == null)
throw new ArgumentNullException("pub");
if (message == null)
throw new ArgumentNullException("message");
if (!pub.Parameters.Equals(dhParams))
throw new ArgumentException("Diffie-Hellman public key has wrong parameters.");
BigInteger p = dhParams.P;
BigInteger y = pub.Y;
if (y == null || y.CompareTo(BigInteger.One) <= 0 || y.CompareTo(p.Subtract(BigInteger.One)) >= 0)
throw new ArgumentException("Diffie-Hellman public key is weak");
BigInteger bigInteger = y.ModPow(privateValue, p);
if (bigInteger.Equals(BigInteger.One))
throw new InvalidOperationException("Shared key can't be 1");
return message.ModPow(key.X, p).Multiply(bigInteger).Mod(p);
}
}
}