/// <summary>
/// Default constructor
/// </summary>
/// <param name="p">First prime number</param>
/// <param name="q">Second prime number</param>
/// <param name="privateKey">Private key d</param>
/// <param name="hashFunction">hashfunction to use in algorithm</param>
/// <param name="ChecksNeeded">check if data is right </param>
public RsaSignature(BigInteger p, BigInteger q, BigInteger privateKey, HashFunction hashFunction, bool ChecksNeeded)
{
if (ChecksNeeded)
{
if ((!p.CheckIfPrime()) || (!q.CheckIfPrime()))
{
throw new ArgumentException("p and q must be prime numbers!");
}
//if privatekey = 1 then signature == h
//if privateKey == phi(n) - 1; then s == 1
//if privateKey > phi(n) then there'll problem with multipl. inversion in equation d*e = 1 mod phi(n)
if ((privateKey < 2) || (privateKey > (p - 1) * (q - 1) - 1))
{
throw new ArgumentException("Private key should be 2 < < (p - 1) * (q - 1) - 1)!");
}
//We need private key to be prime with phi(n) to find open key later
if (!NumericAlgorithms.GCD(privateKey, (p - 1) * (q - 1)).Equals(1))
{
throw new ArgumentException("D should be mutually prime with (p - 1) * (q - 1)");
}
}
Modulus = p * q;
PublicExp = NumericAlgorithms.ExtendedGCD((p - 1) * (q - 1), privateKey);
PrivateExp = privateKey;
HashFunc = (hashFunction == HashFunction.MD5) ? null : new HashFunctionFactory().NewHashFunction(Modulus, hashFunction);
}
private BigInteger[] Decrypt(BigInteger FirstPrime, BigInteger SecondPrime, BigInteger cipherText)
{
var publicKey = CalculatePublicKey(FirstPrime, SecondPrime);
if (cipherText > publicKey)
{
throw new ArgumentException("c", "Ciphertext is larger than public key");
}
BigInteger r = NumericAlgorithms.FastExp(cipherText, (FirstPrime + 1) / 4, FirstPrime);
BigInteger s = NumericAlgorithms.FastExp(cipherText, (SecondPrime + 1) / 4, SecondPrime);
BigInteger a, b;
NumericAlgorithms.ExtendedGCD(FirstPrime, SecondPrime, out a, out b);
//(a*p*r + b*q*s) % n
BigInteger m1 = (a * FirstPrime * s + b * SecondPrime * r) % publicKey;
if (m1 < 0)
{
m1 += publicKey;
}
BigInteger m2 = publicKey - m1;
BigInteger m3 = (a * FirstPrime * s - b * SecondPrime * r) % publicKey;
if (m3 < 0)
{
m3 += publicKey;
}
BigInteger m4 = publicKey - m3;
return(new BigInteger[] { m1, m2, m3, m4 });
}
private int[] Decrypt(int FirstPrime, int SecondPrime, int b, int cipherText)
{
var publicKey = CalculatePublicKey(FirstPrime, SecondPrime);
if (cipherText > publicKey)
{
throw new ArgumentException("cipherText", "Ciphertext is larger then public key");
}
var D = (b * b + (4 * cipherText)) % publicKey;
int mp = NumericAlgorithms.FastExp(D, (FirstPrime + 1) / 4, FirstPrime);
int mq = NumericAlgorithms.FastExp(D, (SecondPrime + 1) / 4, SecondPrime);
NumericAlgorithms.ExtendedGCD(FirstPrime, SecondPrime, out int yp, out int yq);
int d1, d2, d3, d4;
d1 = (yp * FirstPrime * mq + yq * SecondPrime * mp) % publicKey;
d1 = (d1 >= 0) ? d1 : NumericAlgorithms.NegativeMod(yp * FirstPrime * mq + yq * SecondPrime * mp, publicKey);
// do { d1 += publicKey; } while (d1 <= 0);
d2 = publicKey - d1;
d3 = (yp * FirstPrime * mq - yq * SecondPrime * mp) % publicKey;
d3 = (d3 >= 0) ? d3 : NumericAlgorithms.NegativeMod(yp * FirstPrime * mq - yq * SecondPrime * mp, publicKey);
//do { d3 += publicKey; } while (d3 <= 0);
d4 = publicKey - d3;
d1 = Math.Abs(CalculateRoot(b, d1, publicKey));
d2 = Math.Abs(CalculateRoot(b, d2, publicKey));
d3 = Math.Abs(CalculateRoot(b, d3, publicKey));
d4 = Math.Abs(CalculateRoot(b, d4, publicKey));
return(new int[] { d1, d2, d3, d4 });
}