using Org.BouncyCastle.Crypto;

using Org.BouncyCastle.Crypto.Digests;

using Org.BouncyCastle.Crypto.Encodings;

using Org.BouncyCastle.Crypto.Engines;

using Org.BouncyCastle.Crypto.Parameters;

using Org.BouncyCastle.OpenSsl;

using System;

using System.IO;

using System.Text;

public class Program

{

    public static void Main()

    {

        byte[] ciphertext = Convert.FromBase64String("g+lxEfyF/n0oxK7IThlqZbe+8SViX4lCtX3zX6WLfNehqs+e2maOXXaG/w2S40RAGJzk5YqFl9pWoIDUwf5LDPSu+YTWFCHE3AHEWYflxDq855fPa/v55bHRCA5lZpIx5omA9/cbUapkY/8SkzXqgHTQH/Y3Bqn0pAsb1gPood2nR5PnycDXlFIquFbw8gvia929iZ7y7Ws6IlkxhBYjfJ+7dY45Z7T3qDfGciZM2NUfSnfnN7hN9zfLOUwMzCRXZvMjB/gJQ6WqP37Qz0g7V+L+drmxmoqcvDEqQ/F4XOmSKxRYcwclKrrPuhxkMy860/QK4MCMnAddTKQEUOBLcA==");

        string pkcs8pem = @"-----BEGIN PRIVATE KEY-----

                        MIIEvQIBADANBgkqhkiG9w0BAQEFAASCBKcwggSjAgEAAoIBAQChnrt21RMvGhec

                        0TNEEUGbC6QQkYL7Lr1waCk1u0SVCPebgB+3/ty72phtM2C5NKcIO3u6i9k1vbW7

                        W+lnAofJWAUQY7hIDxE2eOEm3YPvPxEMxZfexqh3LuOj1MqWs8AEtkajajy9p1bw

                        OXL+/4h3RgOF4KRUKgIR5SNDyShdmFPCFiQY+76+R2KpflxRqJVO7W7O3n3Vo7lX

                        D+FXgMiEUqc5OdheeleLBHC0/JigZNrrjJZ+La3Ru/32rPQGAONCMPRyK8J7wtFc

                        YaHIHVTVoeMMMYSe6VNgnISoLM0bAGnMQdSOog5cSUWO3nkAUakIcC7K6heg/eBC

                        +hKPpEKxAgMBAAECggEAahiXm6S4mT0Zrxot+0sQtEVqCG5de6LtPTNDikBK/0MJ

                        uIzdRZ4LLU6MrXMC1dHYrLDPwmA30O2etUXa7IJevTAI8v9jY/pwJEAqHadhCtdt

                        y+KSle33fXXMfioca93H+c/mgzQkd6O4kK5F7Vu2LAZMHcCgX5fMEA9JnSAaXYWo

                        NDuouqrAb1ev7vxJMt03xQ5QKwpXep1Mzo1ct5eWIjRcgVCBPpcyJEYS+ElVpRMn

                        /erbfHNrzuTyOmoayHkCu2cbotQ43bqsR50EvaiZ7sc1X4g5HXjc9dWsEzKfqqfA

                        Bqz5m35Z8JsEI/STrygvubMuY/ojNjgoET0EUSjTgQKBgQD0YyCLZeb06qNSaKEy

                        3Sg+c9wzHQNH7iZl7M9UQPZ/eBqs4pxa85XLU38yfkD0vvzmM+NYT66LuLkNPoAw

                        mJbGR4R1iNeZmGkb0jemFrXJovMFeOX4OuL90JdnFCr5ntrGcHHAiEM0cB54IBq7

                        qEt/OwaC/lgC9J6DopTsB/Xp2QKBgQCpTMaO9nF9X/ao8x02H2hRy9VshycimGdM

                        /UxrsEAPpqdOdKu7YQMtHrrKJG12sL0Tnh3jFZ5M0exJRxpAGQCzKnsKl7CDLi+a

                        jwYTepS73UmTf/Vk3qPEvIyhqTLOFhOarixCxM8LV1pReqlGMZjM//x0wzOUpDZW

                        dyn7YFeAmQKBgQCKfMnqdJqGW5ilkGkYu76cdWdpB53eWxQjWii7I/0LivIC2n+k

                        Arj1+aDw6h7BEqGZifnhB3Zv8wPaf3qBD1cRkWF8gUk73uRhQaULV384fkCc7z/S

                        hPwwvM2vOfyIa/6pyPqNEiqTQp3hkL/Va68ssDQmcx9IvXo+OhmOD4zJMQKBgFGr

                        jtGigycHJxdjiED2r71dxkw/epqOyK50NuxwLsceDvGjCMEw0HZwr40aO5AZPGz9

                        Rs+oOyA12HWVDk3DgfnsUUTP3j+6BQ7bVgQJizyBSKAWB0wstvYOOw01cSPHtJdW

                        1FU1WefPsOtDb+tDu8GQ77ln/TcEbI4TmDYCyNNpAoGAMultc3and65tAYmq/8rp

                        //0sG7H9FYZedn4LWgK0atSP4lrw3r5x3oYzP0ajTQYJ0JRlcHLHqsBlBrDuRZwj

                        rjqaJqmVfhi1tfV3abBueabP0QfhpGHN1vL1UOg9cGB/h25+A2hLfE/g1Lgfmg+D

                        SA9LS/ClaylaqmUsz43+QaM=

                        -----END PRIVATE KEY-----";

​

        test_rsaKeyParameters(pkcs8pem, ciphertext);

        test_assymetricKeyParameter(pkcs8pem, ciphertext);

        test_iCipherParameters(pkcs8pem, ciphertext);

    }

    private static void test_rsaKeyParameters(string pkcs8pem, byte[] ciphertext)

    {

        PemReader pemReader = new PemReader(new StringReader(pkcs8pem));

        RsaKeyParameters rsaKeyParameters = (RsaKeyParameters)pemReader.ReadObject();

​

        OaepEncoding oaepEncoding = new OaepEncoding(new RsaEngine(), new Sha256Digest(), new Sha1Digest(), null);

        oaepEncoding.Init(false, rsaKeyParameters);

        byte[] decrypted = oaepEncoding.ProcessBlock(ciphertext, 0, ciphertext.Length);

​

        Console.WriteLine(Encoding.UTF8.GetString(decrypted));

    }

​

    private static void test_assymetricKeyParameter(string pkcs8pem, byte[] ciphertext)

    {

        PemReader pemReader = new PemReader(new StringReader(pkcs8pem));

        AsymmetricKeyParameter asymmetricKeyParameter = (AsymmetricKeyParameter)pemReader.ReadObject();

​

        OaepEncoding oaepEncoding = new OaepEncoding(new RsaEngine(), new Sha256Digest(), new Sha1Digest(), null);

        oaepEncoding.Init(false, asymmetricKeyParameter);

        byte[] decrypted = oaepEncoding.ProcessBlock(ciphertext, 0, ciphertext.Length);

​

        Console.WriteLine(Encoding.UTF8.GetString(decrypted));

    }

​

    private static void test_iCipherParameters(string pkcs8pem, byte[] ciphertext)

    {

        PemReader pemReader = new PemReader(new StringReader(pkcs8pem));

        ICipherParameters iCipherParameters = (ICipherParameters)pemReader.ReadObject();

​

        OaepEncoding oaepEncoding = new OaepEncoding(new RsaEngine(), new Sha256Digest(), new Sha1Digest(), null);

        oaepEncoding.Init(false, iCipherParameters);

        byte[] decrypted = oaepEncoding.ProcessBlock(ciphertext, 0, ciphertext.Length);

​

        Console.WriteLine(Encoding.UTF8.GetString(decrypted));

    }

}