90 lines
2.5 KiB
C#
90 lines
2.5 KiB
C#
using System;
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using System.Diagnostics;
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using Org.BouncyCastle.Crypto.Parameters;
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using Org.BouncyCastle.Math;
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using Org.BouncyCastle.Security;
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namespace Org.BouncyCastle.Crypto.Agreement
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{
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/**
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* a Diffie-Hellman key exchange engine.
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* <p>
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* note: This uses MTI/A0 key agreement in order to make the key agreement
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* secure against passive attacks. If you're doing Diffie-Hellman and both
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* parties have long term public keys you should look at using this. For
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* further information have a look at RFC 2631.</p>
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* <p>
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* It's possible to extend this to more than two parties as well, for the moment
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* that is left as an exercise for the reader.</p>
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*/
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public class DHAgreement
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{
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private DHPrivateKeyParameters key;
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private DHParameters dhParams;
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private BigInteger privateValue;
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private SecureRandom random;
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public void Init(
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ICipherParameters parameters)
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{
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AsymmetricKeyParameter kParam;
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if (parameters is ParametersWithRandom)
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{
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ParametersWithRandom rParam = (ParametersWithRandom)parameters;
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this.random = rParam.Random;
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kParam = (AsymmetricKeyParameter)rParam.Parameters;
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}
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else
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{
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this.random = new SecureRandom();
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kParam = (AsymmetricKeyParameter)parameters;
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}
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if (!(kParam is DHPrivateKeyParameters))
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{
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throw new ArgumentException("DHEngine expects DHPrivateKeyParameters");
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}
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this.key = (DHPrivateKeyParameters)kParam;
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this.dhParams = key.Parameters;
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}
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/**
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* calculate our initial message.
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*/
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public BigInteger CalculateMessage()
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{
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int bits = dhParams.P.BitLength - 1;
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// TODO Should the generated numbers always have length 'P.BitLength - 1'?
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this.privateValue = new BigInteger(bits, random).SetBit(bits - 1);
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return dhParams.G.ModPow(privateValue, dhParams.P);
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}
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/**
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* given a message from a given party and the corresponding public key
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* calculate the next message in the agreement sequence. In this case
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* this will represent the shared secret.
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*/
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public BigInteger CalculateAgreement(
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DHPublicKeyParameters pub,
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BigInteger message)
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{
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if (pub == null)
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throw new ArgumentNullException("pub");
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if (message == null)
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throw new ArgumentNullException("message");
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if (!pub.Parameters.Equals(dhParams))
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{
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throw new ArgumentException("Diffie-Hellman public key has wrong parameters.");
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}
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return message.ModPow(key.X, dhParams.P).Multiply(pub.Y.ModPow(privateValue, dhParams.P)).Mod(dhParams.P);
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}
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}
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}
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