Question

I need to encrypt a string using an RSA 1.5 algorithm. I have been provided with a private key. However, I cannot for the life of me figure out how to add this key to the class. It seems as tho the key needs to be of type RSAParameter stuct. However this requires a set of values I have not been given such as Modulus, Exponent, P, Q, etc.. All I have is the private key. Can anyone help?

Answer 1

You should be aware of the Bouncycastle C# library. There are in particular two very useful classes: Org.BouncyCastle.OpenSsl.PemReader which will convert from the openssl style key you have to a bouncycastle key object, and Org.BouncyCastle.Security.DotNetUtilities, which will convert a bouncycastle key to a .NET RSAParameters object.

Here is a tiny bit of untested code that shows how to use it

using System;
using System.IO;
using System.Security.Cryptography;
using Org.BouncyCastle.OpenSsl;
using Org.BouncyCastle.Crypto;
using Org.BouncyCastle.Security;
using Org.BouncyCastle.Crypto.Parameters;

namespace RSAOpensslToDotNet
{
    class Program
    {
        static void Main(string[] args)
        {
            StreamReader sr = new StreamReader("../../privatekey.pem");
            PemReader pr = new PemReader(sr);
            AsymmetricCipherKeyPair KeyPair = (AsymmetricCipherKeyPair)pr.ReadObject();
            RSAParameters rsa = DotNetUtilities.ToRSAParameters((RsaPrivateCrtKeyParameters)KeyPair.Private);
        }
    }
}