using Org.BouncyCastle.Asn1.Pkcs;
using Org.BouncyCastle.Asn1.X509;
using Org.BouncyCastle.Crypto;
using Org.BouncyCastle.Crypto.Encodings;
using Org.BouncyCastle.Crypto.Engines;
using Org.BouncyCastle.Crypto.Parameters;
using Org.BouncyCastle.OpenSsl;
using Org.BouncyCastle.Pkcs;
using Org.BouncyCastle.X509;
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.IO;
using System.Linq;
using System.Security.Cryptography;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace Sifreleme2
{
    public partial class Form1 : Form
    {

        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            string plainText = "TeknoSeyir";

            string cihperText = encrypt(plainText);
            string decryptedCipherText = decrypt(cihperText);

            Console.WriteLine("Encrypted text: {0}", cihperText);
            Console.WriteLine("Decrypted text {0}. Encryption/Decryption was correct {1}",
                decryptedCipherText, (plainText == decryptedCipherText).ToString());
        }

        static string encrypt(string plainText)
        {
            byte[] plainTextBytes = Encoding.UTF8.GetBytes(plainText);

            PemReader pr = new PemReader(
                (StreamReader)File.OpenText("./public.pem")
            );
            RsaKeyParameters keys = (RsaKeyParameters)pr.ReadObject();

            // Pure mathematical RSA implementation
            // RsaEngine eng = new RsaEngine();

            // PKCS1 v1.5 paddings
            // Pkcs1Encoding eng = new Pkcs1Encoding(new RsaEngine());

            // PKCS1 OAEP paddings
            OaepEncoding eng = new OaepEncoding(new RsaEngine());
            eng.Init(true, keys);

            int length = plainTextBytes.Length;
            int blockSize = eng.GetInputBlockSize();
            List<byte> cipherTextBytes = new List<byte>();
            for (int chunkPosition = 0;
                chunkPosition < length;
                chunkPosition += blockSize)
            {
                int chunkSize = Math.Min(blockSize, length - chunkPosition);
                cipherTextBytes.AddRange(eng.ProcessBlock(
                    plainTextBytes, chunkPosition, chunkSize
                ));
            }
            return Convert.ToBase64String(cipherTextBytes.ToArray());
        }

        static string decrypt(string cipherText)
        {
            byte[] cipherTextBytes = Convert.FromBase64String(cipherText);

            PemReader pr = new PemReader(
                (StreamReader)File.OpenText("./private.pem")
            );
            AsymmetricCipherKeyPair keys = (AsymmetricCipherKeyPair)pr.ReadObject();

            // Pure mathematical RSA implementation
            // RsaEngine eng = new RsaEngine();

            // PKCS1 v1.5 paddings
            // Pkcs1Encoding eng = new Pkcs1Encoding(new RsaEngine());

            // PKCS1 OAEP paddings
            OaepEncoding eng = new OaepEncoding(new RsaEngine());
            eng.Init(false, keys.Private);

            int length = cipherTextBytes.Length;
            int blockSize = eng.GetInputBlockSize();
            List<byte> plainTextBytes = new List<byte>();
            for (int chunkPosition = 0;
                chunkPosition < length;
                chunkPosition += blockSize)
            {
                int chunkSize = Math.Min(blockSize, length - chunkPosition);
                plainTextBytes.AddRange(eng.ProcessBlock(
                    cipherTextBytes, chunkPosition, chunkSize
                ));
            }
            return Encoding.UTF8.GetString(plainTextBytes.ToArray());
        }
    }
}