/// <summary>
/// Creates a new ElGamal secret key and returns it as a
/// 2 dimensional array of biginteger. return[0] holds
/// the public values of the key and return[1] all the
/// secret values.
/// </summary>
/// <remarks>
/// Creates a new ElGamal secret key and returns it as a
/// 2 dimensional array of biginteger. return[0] holds
/// the public values of the key and return[1] all the
/// secret values.<br></br>
/// The order of the public components is p, g, y
/// The order of the secret components is x.
/// </remarks>
/// <param name="nbits">The size of the key in bits.</param>
/// <returns>A new ElGamal secret key and returns it as a
/// 2 dimensional array of biginteger. return[0] holds
/// the public values of the key and return[1] all the
/// secret values.<br></br>
/// The order of the public components is p, g, y
/// The order of the secret components is x.
/// </returns>
public override BigInteger[][] Generate(int nBits)
{
EG_Secret_Key eskKey = GenerateKey(nBits);
biGeneratedKey = new BigInteger[2][];
biGeneratedKey[0] = new BigInteger[3];
biGeneratedKey[0][0] = eskKey.p;
biGeneratedKey[0][1] = eskKey.g;
biGeneratedKey[0][2] = eskKey.y;
biGeneratedKey[1] = new BigInteger[1];
biGeneratedKey[1][0] = eskKey.x;
return(biGeneratedKey);
}
private EG_Secret_Key GenerateKey(int nBits)
{
BigInteger q = new BigInteger();
BigInteger p;
BigInteger g;
BigInteger gPowTwo;
BigInteger gPowQ;
EG_Secret_Key eskKey = new EG_Secret_Key();
/*
* // construct a prime p = 2q + 1
* do {
* q = BigInteger.genRandom(nBits - 1);
* System.Windows.Forms.Application.DoEvents();
* p = (2*q) + 1;
* } while ((!p.isProbablePrime()) || (!q.isProbablePrime()));
*/
q = BigInteger.genPseudoPrime(nBits - 1);
p = BigInteger.genPseudoPrime(nBits);
// find a generator
do
{
g = new BigInteger();
g = BigInteger.genRandom(nBits - 1);
gPowTwo = g.modPow(new BigInteger(2), p);
gPowQ = g.modPow(q, p);
} while ((gPowTwo == 1) || (gPowQ == 1));
BigInteger x;
do
{
x = new BigInteger();
x = BigInteger.genRandom(nBits);
} while (x >= p - 1);
BigInteger y = g.modPow(x, p);
eskKey.p = p;
eskKey.g = g;
eskKey.x = x;
eskKey.y = y;
return(eskKey);
}
/// <summary>
/// Secret key operation. Decrypts biCipher with the keydata
/// in the given secret key packet.
/// </summary>
/// <param name="biInput">The ciphertext that is about to
/// be decrypted</param>
/// <param name="skpKey">The secret key packet with the key
/// material for the decryption</param>
/// <param name="strPassphrase">The passphrase for the
/// keymaterial</param>
/// <returns>The decrypted ciphertext.</returns>
/// <remarks>No remarks.</remarks>
public override BigInteger Decrypt(BigInteger[] biInput, SecretKeyPacket skpKey, string strPassphrase)
{
BigInteger[] biKeyMaterial = skpKey.GetDecryptedKeyMaterial(strPassphrase);
EG_Secret_Key eskKey = new EG_Secret_Key();
eskKey.x = biKeyMaterial[0];
eskKey.p = skpKey.PublicKey.KeyMaterial[0];
eskKey.g = skpKey.PublicKey.KeyMaterial[1];
eskKey.y = skpKey.PublicKey.KeyMaterial[2];
if (biInput.Length != 2)
throw new ArgumentException("biInput is not an ElGamal encrypted Packet");
BigInteger B = biInput[0];
BigInteger c = biInput[1];
BigInteger z = B.modPow(eskKey.x, eskKey.p).modInverse(eskKey.p);
BigInteger output = (z * c) % eskKey.p;
return output;
}
/// <summary>
/// Secret key operation. Decrypts biCipher with the keydata
/// in the given secret key packet.
/// </summary>
/// <param name="biInput">The ciphertext that is about to
/// be decrypted</param>
/// <param name="skpKey">The secret key packet with the key
/// material for the decryption</param>
/// <param name="strPassphrase">The passphrase for the
/// keymaterial</param>
/// <returns>The decrypted ciphertext.</returns>
/// <remarks>No remarks.</remarks>
public override BigInteger Decrypt(BigInteger[] biInput, SecretKeyPacket skpKey, string strPassphrase)
{
BigInteger[] biKeyMaterial = skpKey.GetDecryptedKeyMaterial(strPassphrase);
EG_Secret_Key eskKey = new EG_Secret_Key();
eskKey.x = biKeyMaterial[0];
eskKey.p = skpKey.PublicKey.KeyMaterial[0];
eskKey.g = skpKey.PublicKey.KeyMaterial[1];
eskKey.y = skpKey.PublicKey.KeyMaterial[2];
if (biInput.Length != 2)
{
throw new ArgumentException("biInput is not an ElGamal encrypted Packet");
}
BigInteger B = biInput[0];
BigInteger c = biInput[1];
BigInteger z = B.modPow(eskKey.x, eskKey.p).modInverse(eskKey.p);
BigInteger output = (z * c) % eskKey.p;
return(output);
}
private EG_Secret_Key GenerateKey(int nBits)
{
BigInteger q = new BigInteger();
BigInteger p;
BigInteger g;
BigInteger gPowTwo;
BigInteger gPowQ;
EG_Secret_Key eskKey = new EG_Secret_Key();
/*
// construct a prime p = 2q + 1
do {
q = BigInteger.genRandom(nBits - 1);
System.Windows.Forms.Application.DoEvents();
p = (2*q) + 1;
} while ((!p.isProbablePrime()) || (!q.isProbablePrime()));
*/
q = BigInteger.genPseudoPrime(nBits - 1);
p = BigInteger.genPseudoPrime(nBits);
// find a generator
do {
g = new BigInteger();
g = BigInteger.genRandom(nBits - 1);
gPowTwo = g.modPow(new BigInteger(2), p);
gPowQ = g.modPow(q, p);
} while ((gPowTwo == 1) || (gPowQ == 1));
BigInteger x;
do {
x = new BigInteger();
x = BigInteger.genRandom(nBits);
} while (x >= p-1);
BigInteger y = g.modPow(x, p);
eskKey.p = p;
eskKey.g = g;
eskKey.x = x;
eskKey.y = y;
return eskKey;
}
