/**
* given a message from a given party and the corresponding public key
* calculate the next message in the agreement sequence. In this case
* this will represent the shared secret.
*/
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;
return message.ModPow(key.X, p).Multiply(pub.Y.ModPow(privateValue, p)).Mod(p);
}
/**
* Process a single block using the basic ElGamal algorithm.
*
* @param in the input array.
* @param inOff the offset into the input buffer where the data starts.
* @param length the length of the data to be processed.
* @return the result of the ElGamal process.
* @exception DataLengthException the input block is too large.
*/
public byte[] ProcessBlock(
byte[] input,
int inOff,
int length)
{
if (key == null)
throw new InvalidOperationException("ElGamal engine not initialised");
int maxLength = forEncryption
? (bitSize - 1 + 7) / 8
: GetInputBlockSize();
if (length > maxLength)
throw new DataLengthException("input too large for ElGamal cipher.\n");
BigInteger p = key.Parameters.P;
byte[] output;
if (key is ElGamalPrivateKeyParameters) // decryption
{
int halfLength = length / 2;
BigInteger gamma = new BigInteger(1, input, inOff, halfLength);
BigInteger phi = new BigInteger(1, input, inOff + halfLength, halfLength);
ElGamalPrivateKeyParameters priv = (ElGamalPrivateKeyParameters) key;
// a shortcut, which generally relies on p being prime amongst other things.
// if a problem with this shows up, check the p and g values!
BigInteger m = gamma.ModPow(p.Subtract(BigInteger.One).Subtract(priv.X), p).Multiply(phi).Mod(p);
output = m.ToByteArrayUnsigned();
}
else // encryption
{
BigInteger tmp = new BigInteger(1, input, inOff, length);
if (tmp.BitLength >= p.BitLength)
throw new DataLengthException("input too large for ElGamal cipher.\n");
ElGamalPublicKeyParameters pub = (ElGamalPublicKeyParameters) key;
BigInteger pSub2 = p.Subtract(BigInteger.Two);
// TODO In theory, a series of 'k', 'g.ModPow(k, p)' and 'y.ModPow(k, p)' can be pre-calculated
BigInteger k;
do
{
k = new BigInteger(p.BitLength, random);
}
while (k.SignValue == 0 || k.CompareTo(pSub2) > 0);
BigInteger g = key.Parameters.G;
BigInteger gamma = g.ModPow(k, p);
BigInteger phi = tmp.Multiply(pub.Y.ModPow(k, p)).Mod(p);
output = new byte[this.GetOutputBlockSize()];
// TODO Add methods to allow writing BigInteger to existing byte array?
byte[] out1 = gamma.ToByteArrayUnsigned();
byte[] out2 = phi.ToByteArrayUnsigned();
out1.CopyTo(output, output.Length / 2 - out1.Length);
out2.CopyTo(output, output.Length - out2.Length);
}
return output;
}
/**
* Procedure C
* procedure generates the a value from the given p,q,
* returning the a value.
*/
private BigInteger procedure_C(BigInteger p, BigInteger q)
{
BigInteger pSub1 = p.Subtract(BigInteger.One);
BigInteger pSub1Divq = pSub1.Divide(q);
for(;;)
{
BigInteger d = new BigInteger(p.BitLength, init_random);
// 1 < d < p-1
if (d.CompareTo(BigInteger.One) > 0 && d.CompareTo(pSub1) < 0)
{
BigInteger a = d.ModPow(pSub1Divq, p);
if (a.CompareTo(BigInteger.One) != 0)
{
return a;
}
}
}
}
public BigInteger ProcessBlock(
BigInteger input)
{
if (key is RsaPrivateCrtKeyParameters)
{
//
// we have the extra factors, use the Chinese Remainder Theorem - the author
// wishes to express his thanks to Dirk Bonekaemper at rtsffm.com for
// advice regarding the expression of this.
//
RsaPrivateCrtKeyParameters crtKey = (RsaPrivateCrtKeyParameters)key;
BigInteger p = crtKey.P;;
BigInteger q = crtKey.Q;
BigInteger dP = crtKey.DP;
BigInteger dQ = crtKey.DQ;
BigInteger qInv = crtKey.QInv;
BigInteger mP, mQ, h, m;
// mP = ((input Mod p) ^ dP)) Mod p
mP = (input.Remainder(p)).ModPow(dP, p);
// mQ = ((input Mod q) ^ dQ)) Mod q
mQ = (input.Remainder(q)).ModPow(dQ, q);
// h = qInv * (mP - mQ) Mod p
h = mP.Subtract(mQ);
h = h.Multiply(qInv);
h = h.Mod(p); // Mod (in Java) returns the positive residual
// m = h * q + mQ
m = h.Multiply(q);
m = m.Add(mQ);
return m;
}
return input.ModPow(key.Exponent, key.Modulus);
}
private static BigInteger CalculatePublicKey(BigInteger p, BigInteger g, BigInteger x)
{
return g.ModPow(x, p);
}
/**
* Set the private key.
*
* @param p key parameter: field modulus
* @param q key parameter: subgroup order
* @param g key parameter: generator
* @param x private key
*/
public void setPrivateKey(BigInteger p, BigInteger q,
BigInteger g, BigInteger x)
{
/*
* Perform some basic sanity checks. We do not
* check primality of p or q because that would
* be too expensive.
*
* We reject keys where q is longer than 999 bits,
* because it would complicate signature encoding.
* Normal DSA keys do not have a q longer than 256
* bits anyway.
*/
if(p == null || q == null || g == null || x == null
|| p.SignValue <= 0 || q.SignValue <= 0
|| g.SignValue <= 0 || x.SignValue <= 0
|| x.CompareTo(q) >= 0 || q.CompareTo(p) >= 0
|| q.BitLength > 999
|| g.CompareTo(p) >= 0 || g.BitLength == 1
|| g.ModPow(q, p).BitLength != 1)
{
throw new InvalidOperationException(
"invalid DSA private key");
}
this.p = p;
this.q = q;
this.g = g;
this.x = x;
qlen = q.BitLength;
if(q.SignValue <= 0 || qlen < 8)
{
throw new InvalidOperationException(
"bad group order: " + q);
}
rolen = (qlen + 7) >> 3;
rlen = rolen * 8;
/*
* Convert the private exponent (x) into a sequence
* of octets.
*/
bx = int2octets(x);
}
