using System;
using System.Collections.Generic,
using System.Text;
using System.IO;
using System.Security.Cryptography;
 
namespace Project
{
 class EncryptedData
 {
  // contains the names of the files where encrypted data will be stored
 
  public string Enc_File
  {
   get {return enc_file};
   set {enc_file = value};
  }
  string enc_file;
 
  public string Enc_Key
  {
   get {return enc_key};
   set {enc_key = value};
  }
  string enc_key;
 
  public string Enc_IV
  {
   get {return enc_IV};
   set {enc_IV = value};
  }
  string enc_IV;
 }
 
 class LetsDoIt
 {
  const int RSA_KEY_SIZE = 4096;
   
  static void Main()
  {
   try
   {
    RSACryptoServiceProvider RSACrypto = new RSACryptoServiceProvider(RSA_KEY_SIZE);
   
    EncryptedData encFiles = new EncryptedData();
 
    encFiles = encrypt("toEncrypt.txt", RSACrypto.ExportParameters(false));
     
    string decFile = decrypt(encFiles, RSACrypto.ExportParameters(true));
   }
   catch (Exception e) { Console.WriteLine("Error in Main: {0}", e.Message); }
  }
 
  static EncryptedData encrypt(string FileToEncrypt, RSAParameters RSAParam)
  {
   try
   {
   // Part 1 : encrypting data
    // 1 : create a Rijndael instance.
    Rijndael rijndaelAlg = Rijndael.Create();
    rijndaelAlg.GenerateKey();
    rijndaelAlg.GenerateIV();
    ICryptoTransformer rijndaelEncryptor = rijndael.CreateEncryptor(rijndaelAlg.Key, rijndaelAlg.IV);
     
    // 2 : open and read file
    FileStream fstf = File.Open(FileToEncrypt, FileMode.OpenOrCreate);
    StreamReader strf = new StreamReader(fst);
    string file_contents = str.ReadToEnd();
 
    EncryptedData encryptedFiles = new EncryptedData();
    encryptedFiles.Enc_File = "encryptedFile";
 
    // 3 : creating a new file, and writing encrypted data into it
    FileStream fstef = new FileSream(encryptedFiles.Enc_File, FileMode.OpenOrCreate);
    CryptoStream cstf = new CryptoStream(fstef, rijndaelEncryptor, CryptoStreamMode.Write);
    StreamWriter stw = new StreamWriter(cstf);
    stw.Write(file_contents);
 
    // 4 : closing streams
    stw.Close();
    cstf.Close();
    fstef.Close();
    strf.Close();
    fstf.Close();
     
   // Part 2 : encrypting keys
    // 1 : create a RSA instance, and import the public keys
    RSACryptoServiceProvider RSA = new RSACryptoServiceProvider(RSA_KEY_SIZE);
    RSA.ImportParameters(RSAParam);
 
    // 2 : encrypt Rijndael keys
    byte[] EncKey_byte = RSA.Encrypt(rijndaelAlg.Key, false);
    byte[] EncIV_byte = RSA.Encrypt(rijndaelAlg.IV, false);
 
    ASCIIEncoding ByteConverter = new ASCIIEncoding();
    string EncKey_string = ByteConverter.GetString(EncKey_byte);
    string EncIV_string = ByteConverter.GetString(EncIV_byte);
     
    // 3 : finally, writing encrypted keys into files
    encryptedFiles.Enc_Key = "encryptedKey";
    encryptedFiles.Enc_IV = "encryptedIV";
    FileStream fstK = new FileStream(encryptedFiles.Enc_Key, FileMode.OpenOrCreate);
    FileStream fstI = new FileStream(encryptedFiles.Enc_IV, FileMode.OpenOrCreate);
    StreamWriter stwK = new StreamWriter(fstK);
    StreamWriter stwI = new StreamWriter(fstI);
    stwK.Write(EncKey_string);
    stwI.Write(EncIV_string);
   
    // 4 : closing streams
    stwK.Close();
    stwI.Close();
    fstK.Close();
    fstI.Close();
   
    return encryptedFiles;
   }
   catch (Exception e) { Console.WriteLine("Error in encrypt: {0}", e.Message); }
  }
 
  static string decrypt(EncryptedData encData, RSAParameters RSAParam)
  {
   try
   {
    // 1 : get files' contents
    FileStream fstK = File.Open(encData.Enc_Key, FileMode.Open);
    FileStream fstI = File.Open(encData.Enc_I, FileMode.Open);
    StreamReader stwK = new StreamReader(fstK);
    StreamReader stwI = new StreamReader(fstI);
     
    string EncKey_string = stwK.ReadToEnd();
    string EncIV_Key = stwI.ReadToEnd();
     
    ASCIIEncoding ByteConverter = new ASCIIEncoding();
    byte[] EncKey_byte = ByteConverter.GetBytes(EncKey_string);
    byte[] EncIV_byte = ByteConverter.GetBytes(EncIV_string);
 
    // 2 : decrypt keys with RSA algorithm
    RSACryptoServiceProvider RSA = RSACryptoServiceProvider();
    RSA.ImportParameters(RSAParam);
 
    byte[] Key_byte = RSA.Decrypt(EncKey_byte, false);
    byte[] IV_byte = RSA.Decrypt(EncIV_byte, false);
   
    // 3 : decrypt the file using the rijndael keys  
    Rijndael rijndaelAlg = Rijndael.Create();
    ICryptoTransform rijndaelDecryptor = rijndaelAlg.CreateDecryptor(Key_byte, IV_byte);
 
    FileStream fstef = File.Open(encData.Enc_File, FileMode.Open);
    CryptoStream cstef = new CryptoStream(fstef, rijndaelDecryptor, CryptoStreamMode.Read);
    StreamReader stref = new StreamReader(cstef);
 
    // 4 : writing retrieved contents into file
    string contents;
    string DecFile = "DecFile.txt";
    FileStream fstf = File.Open(DecFile, FileMode.OpenOrCreate);
    StreamWriter stwf = new StreamWriter(fstf);
 
    contents = stref.ReadToEnd();
    stwf.Write(contents);
 
    // 5 : closing streams
    stwf.Close();
    fstf.Close();
    stref.Close();
    cstef.Close();
    stwK.Close();
    stwI.Close();
    fstK.Close();
    fstI.Close();
 
    return DecFile;
   }
   catch (Exception e) { Console.WriteLine("Error in decrypt: {0}", e.Message); }
  }
 }
}