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using System;
using Org.BouncyCastle.Crypto.Parameters;
using Org.BouncyCastle.Math;
using Org.BouncyCastle.Security;
namespace Org.BouncyCastle.Crypto.Signers
{
/**
* Gost R 34.10-94 Signature Algorithm
*/
public class Gost3410Signer
: IDsa
{
private Gost3410KeyParameters key;
private SecureRandom random;
public virtual string AlgorithmName
{
get { return "GOST3410"; }
}
public virtual 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 Gost3410PrivateKeyParameters))
throw new InvalidKeyException("GOST3410 private key required for signing");
this.key = (Gost3410PrivateKeyParameters) parameters;
}
else
{
if (!(parameters is Gost3410PublicKeyParameters))
throw new InvalidKeyException("GOST3410 public key required for signing");
this.key = (Gost3410PublicKeyParameters) parameters;
}
}
/**
* generate a signature for the given message using the key we were
* initialised with. For conventional Gost3410 the message should be a Gost3411
* hash of the message of interest.
*
* @param message the message that will be verified later.
*/
public virtual BigInteger[] GenerateSignature(
byte[] message)
{
byte[] mRev = new byte[message.Length]; // conversion is little-endian
for (int i = 0; i != mRev.Length; i++)
{
mRev[i] = message[mRev.Length - 1 - i];
}
BigInteger m = new BigInteger(1, mRev);
Gost3410Parameters parameters = key.Parameters;
BigInteger k;
do
{
k = new BigInteger(parameters.Q.BitLength, random);
}
while (k.CompareTo(parameters.Q) >= 0);
BigInteger r = parameters.A.ModPow(k, parameters.P).Mod(parameters.Q);
BigInteger s = k.Multiply(m).
Add(((Gost3410PrivateKeyParameters)key).X.Multiply(r)).
Mod(parameters.Q);
return new BigInteger[]{ r, s };
}
/**
* return true if the value r and s represent a Gost3410 signature for
* the passed in message for standard Gost3410 the message should be a
* Gost3411 hash of the real message to be verified.
*/
public virtual bool VerifySignature(
byte[] message,
BigInteger r,
BigInteger s)
{
byte[] mRev = new byte[message.Length]; // conversion is little-endian
for (int i = 0; i != mRev.Length; i++)
{
mRev[i] = message[mRev.Length - 1 - i];
}
BigInteger m = new BigInteger(1, mRev);
Gost3410Parameters parameters = key.Parameters;
if (r.SignValue < 0 || parameters.Q.CompareTo(r) <= 0)
{
return false;
}
if (s.SignValue < 0 || parameters.Q.CompareTo(s) <= 0)
{
return false;
}
BigInteger v = m.ModPow(parameters.Q.Subtract(BigInteger.Two), parameters.Q);
BigInteger z1 = s.Multiply(v).Mod(parameters.Q);
BigInteger z2 = (parameters.Q.Subtract(r)).Multiply(v).Mod(parameters.Q);
z1 = parameters.A.ModPow(z1, parameters.P);
z2 = ((Gost3410PublicKeyParameters)key).Y.ModPow(z2, parameters.P);
BigInteger u = z1.Multiply(z2).Mod(parameters.P).Mod(parameters.Q);
return u.Equals(r);
}
}
}
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