using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Security;
using System.Security.Cryptography;
using System.IO;
using System.Security.Permissions;
using System.Runtime.InteropServices;

namespace SafeConverter
{
    class Cryption
    {
        //  Call this function to remove the key from memory after use for security
        [System.Runtime.InteropServices.DllImport("KERNEL32.DLL", EntryPoint = "RtlZeroMemory")]
        public static extern bool ZeroMemory(IntPtr Destination, int Length);

        // Function to Generate a 64 bits Key.
        static string GenerateKey()
        {
            // Create an instance of Symetric Algorithm. Key and IV is generated automatically.
            DESCryptoServiceProvider desCrypto = (DESCryptoServiceProvider)DESCryptoServiceProvider.Create();

            // Use the Automatically generated key for Encryption.
            return ASCIIEncoding.ASCII.GetString(desCrypto.Key);
        }

        static void EncryptFile(string sInputFilename,
           string sOutputFilename,
           string sKey)
        {
            FileStream fsInput = new FileStream(sInputFilename,
               FileMode.Open,
               FileAccess.Read);

            FileStream fsEncrypted = new FileStream(sOutputFilename,
               FileMode.Create,
               FileAccess.Write);
            DESCryptoServiceProvider DES = new DESCryptoServiceProvider();
            DES.Key = ASCIIEncoding.ASCII.GetBytes(sKey);
            DES.IV = ASCIIEncoding.ASCII.GetBytes(sKey);
            ICryptoTransform desencrypt = DES.CreateEncryptor();
            CryptoStream cryptostream = new CryptoStream(fsEncrypted,
               desencrypt,
               CryptoStreamMode.Write);

            byte[] bytearrayinput = new byte[fsInput.Length];
            fsInput.Read(bytearrayinput, 0, bytearrayinput.Length);
            cryptostream.Write(bytearrayinput, 0, bytearrayinput.Length);
            cryptostream.Close();
            fsInput.Close();
            fsEncrypted.Close();
        }

        static void DecryptFile(string sInputFilename,
           string sOutputFilename,
           string sKey)
        {
            DESCryptoServiceProvider DES = new DESCryptoServiceProvider();
            //A 64 bit key and IV is required for this provider.
            //Set secret key For DES algorithm.
            DES.Key = ASCIIEncoding.ASCII.GetBytes(sKey);
            //Set initialization vector.
            DES.IV = ASCIIEncoding.ASCII.GetBytes(sKey);

            //Create a file stream to read the encrypted file back.
            FileStream fsread = new FileStream(sInputFilename,
               FileMode.Open,
               FileAccess.Read);
            //Create a DES decryptor from the DES instance.
            ICryptoTransform desdecrypt = DES.CreateDecryptor();
            //Create crypto stream set to read and do a
            //DES decryption transform on incoming bytes.
            CryptoStream cryptostreamDecr = new CryptoStream(fsread,
               desdecrypt,
               CryptoStreamMode.Read);
            //Print the contents of the decrypted file.
            StreamWriter fsDecrypted = new StreamWriter(sOutputFilename);
            fsDecrypted.Write(new StreamReader(cryptostreamDecr).ReadToEnd());
            fsDecrypted.Flush();
            fsDecrypted.Close();
        }

        public static void encrypt(String filename)
        {
            // Must be 64 bits, 8 bytes.
            // Distribute this key to the user who will decrypt this file.
            string sSecretKey;
            // Get the Key for the file to Encrypt.
            sSecretKey = GenerateKey();
            // For additional security Pin the key.
            GCHandle gch = GCHandle.Alloc(sSecretKey, GCHandleType.Pinned);
            String[] array = filename.Split('.');
            String newfile = array[0];
            EncryptFile(@filename,@newfile + "EN.txt",sSecretKey);
            // Remove the Key from memory.
            ZeroMemory(gch.AddrOfPinnedObject(), sSecretKey.Length * 2);
            gch.Free();
        }

        public static void decrypt(String filename)
        {
            // Must be 64 bits, 8 bytes.
            // Distribute this key to the user who will decrypt this file.
            string sSecretKey;
            // Get the Key for the file to Encrypt.
            sSecretKey = GenerateKey();
            // For additional security Pin the key.
            GCHandle gch = GCHandle.Alloc(sSecretKey, GCHandleType.Pinned);
            String[] array = filename.Split('.');
            String newfile = array[0];
            DecryptFile(@filename, @newfile + "DE.txt", sSecretKey);
            // Remove the Key from memory.
            ZeroMemory(gch.AddrOfPinnedObject(), sSecretKey.Length * 2);
            gch.Free();
        }

        private static String getRandomFileAss()
        {
            int maxSize = 5;
            char[] chars = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890".ToCharArray();
            byte[] data = new byte[1];
            RNGCryptoServiceProvider crypto = new RNGCryptoServiceProvider();
            crypto.GetNonZeroBytes(data);
            data = new byte[maxSize];
            crypto.GetNonZeroBytes(data);
            StringBuilder result = new StringBuilder(maxSize);
            foreach (byte b in data)
            {
                result.Append(chars[b % (chars.Length - 1)]);
            }
            return result.ToString();
        }
    }

}