/// <summary>
/// Mask Generation Function
/// </summary>
/// <param name="Z">Initial pseudorandom Seed.</param>
/// <param name="l">Length of output required.</param>
/// <returns></returns>
private byte[] MGF(byte[] Z, int l)
{
if (l > (Math.Pow(2, 32)))
{
throw new ArgumentException("Mask too long.");
}
else
{
List <byte> result = new List <byte>();
for (int i = 0; i <= l / rsaParams.hLen; i++)
{
List <byte> data = new List <byte>();
data.AddRange(Z);
data.AddRange(RSAxUtils.I2OSP(i, 4, false));
result.AddRange(rsaParams.ComputeHash(data.ToArray()));
}
if (l <= result.Count)
{
return(result.GetRange(0, l).ToArray());
}
else
{
throw new ArgumentException("Invalid Mask Length.");
}
}
}
/// <summary>
/// Low level RSA Process function for use with private key.
/// Should never be used; Because without padding RSA is vulnerable to attacks. Use with caution.
/// </summary>
/// <param name="PlainText">Data to encrypt. Length must be less than Modulus size in octets.</param>
/// <param name="usePrivate">True to use Private key, else Public.</param>
/// <returns>Encrypted Data</returns>
public byte[] RSAProcess(byte[] PlainText, bool usePrivate)
{
if (usePrivate && (!rsaParams.Has_PRIVATE_Info))
{
throw new CryptographicException("RSA Process: Incomplete Private Key Info");
}
if ((usePrivate == false) && (!rsaParams.Has_PUBLIC_Info))
{
throw new CryptographicException("RSA Process: Incomplete Public Key Info");
}
BigInteger _E;
if (usePrivate)
{
_E = rsaParams.D;
}
else
{
_E = rsaParams.E;
}
BigInteger PT = RSAxUtils.OS2IP(PlainText, false);
BigInteger M = BigInteger.ModPow(PT, _E, rsaParams.N);
if (M.Sign == -1)
{
return(RSAxUtils.I2OSP(M + rsaParams.N, rsaParams.OctetsInModulus, false));
}
else
{
return(RSAxUtils.I2OSP(M, rsaParams.OctetsInModulus, false));
}
}
/// <summary>
/// Low level RSA Decryption function for use with private key. Uses CRT and is Much faster.
/// Should never be used; Because without padding RSA is vulnerable to attacks. Use with caution.
/// </summary>
/// <param name="Data">Data to encrypt. Length must be less than Modulus size in octets.</param>
/// <returns>Encrypted Data</returns>
public byte[] RSADecryptPrivateCRT(byte[] Data)
{
if (rsaParams.Has_PRIVATE_Info && rsaParams.HasCRTInfo)
{
BigInteger C = RSAxUtils.OS2IP(Data, false);
BigInteger M1 = BigInteger.ModPow(C, rsaParams.DP, rsaParams.P);
BigInteger M2 = BigInteger.ModPow(C, rsaParams.DQ, rsaParams.Q);
BigInteger H = ((M1 - M2) * rsaParams.InverseQ) % rsaParams.P;
BigInteger M = (M2 + (rsaParams.Q * H));
if (M.Sign == -1)
{
return(RSAxUtils.I2OSP(M + rsaParams.N, rsaParams.OctetsInModulus, false));
}
else
{
return(RSAxUtils.I2OSP(M, rsaParams.OctetsInModulus, false));
}
}
else
{
throw new CryptographicException("RSA Decrypt CRT: Incomplete Key Info");
}
}
