using System;

public class Program

{

    public static void Main()

    {

        Console.WriteLine("Hello World");

    }

    #region main

        private void button1_Click(object sender, EventArgs e)

        {

            string myString;

            using (FileStream fs = new FileStream(Path.Combine(Path.GetDirectoryName(Assembly.GetExecutingAssembly().Location), @"test.7z"), FileMode.Open))

            using (BinaryReader br = new BinaryReader(fs))

            {

                byte[] bin = br.ReadBytes(Convert.ToInt32(fs.Length));

                myString = Convert.ToBase64String(bin);

            }

​

            string encryptedstring = StringCipher.Encrypt(myString, textBox1.Text);

​

            richTextBox1.Text = encryptedstring;

        }

​

        private void button2_Click(object sender, EventArgs e)

        {

            string decryptedstring = StringCipher.Decrypt(richTextBox1.Text, textBox1.Text);

​

            byte[] rebin = Convert.FromBase64String(decryptedstring);

            using (FileStream fs2 = new FileStream(Path.Combine(Path.GetDirectoryName(Assembly.GetExecutingAssembly().Location), @"test_out.7z"), FileMode.Create))

            using (BinaryWriter bw = new BinaryWriter(fs2))

                bw.Write(rebin);

        }

​

        public static class StringCipher

        {

            // This constant is used to determine the keysize of the encryption algorithm in bits.

            // We divide this by 8 within the code below to get the equivalent number of bytes.

            private const int Keysize = 256;

​

            // This constant determines the number of iterations for the password bytes generation function.

            private const int DerivationIterations = 1000;

​

            public static string Encrypt(string plainText, string passPhrase)

            {

                // Salt and IV is randomly generated each time, but is preprended to encrypted cipher text

                // so that the same Salt and IV values can be used when decrypting.  

                var saltStringBytes = Generate256BitsOfRandomEntropy();

                var ivStringBytes = Generate256BitsOfRandomEntropy();

                var plainTextBytes = Encoding.UTF8.GetBytes(plainText);

                using (var password = new Rfc2898DeriveBytes(passPhrase, saltStringBytes, DerivationIterations))

                {

                    var keyBytes = password.GetBytes(Keysize / 8);

                    using (var symmetricKey = new RijndaelManaged())

                    {

                        symmetricKey.BlockSize = 256;

                        symmetricKey.Mode = CipherMode.CBC;

                        symmetricKey.Padding = PaddingMode.PKCS7;

                        using (var encryptor = symmetricKey.CreateEncryptor(keyBytes, ivStringBytes))

                        {

                            using (var memoryStream = new MemoryStream())

                            {

                                using (var cryptoStream = new CryptoStream(memoryStream, encryptor, CryptoStreamMode.Write))

                                {

                                    cryptoStream.Write(plainTextBytes, 0, plainTextBytes.Length);

                                    cryptoStream.FlushFinalBlock();

                                    // Create the final bytes as a concatenation of the random salt bytes, the random iv bytes and the cipher bytes.

                                    var cipherTextBytes = saltStringBytes;

                                    cipherTextBytes = cipherTextBytes.Concat(ivStringBytes).ToArray();

                                    cipherTextBytes = cipherTextBytes.Concat(memoryStream.ToArray()).ToArray();

                                    memoryStream.Close();

                                    cryptoStream.Close();

                                    return Convert.ToBase64String(cipherTextBytes);

                                }

                            }

                        }

                    }

                }

            }

​

            public static string Decrypt(string cipherText, string passPhrase)

            {

                // Get the complete stream of bytes that represent:

                // [32 bytes of Salt] + [32 bytes of IV] + [n bytes of CipherText]

                var cipherTextBytesWithSaltAndIv = Convert.FromBase64String(cipherText);

                // Get the saltbytes by extracting the first 32 bytes from the supplied cipherText bytes.

                var saltStringBytes = cipherTextBytesWithSaltAndIv.Take(Keysize / 8).ToArray();

                // Get the IV bytes by extracting the next 32 bytes from the supplied cipherText bytes.

                var ivStringBytes = cipherTextBytesWithSaltAndIv.Skip(Keysize / 8).Take(Keysize / 8).ToArray();

                // Get the actual cipher text bytes by removing the first 64 bytes from the cipherText string.

                var cipherTextBytes = cipherTextBytesWithSaltAndIv.Skip((Keysize / 8) * 2).Take(cipherTextBytesWithSaltAndIv.Length - ((Keysize / 8) * 2)).ToArray();

​

                using (var password = new Rfc2898DeriveBytes(passPhrase, saltStringBytes, DerivationIterations))

                {

                    var keyBytes = password.GetBytes(Keysize / 8);

                    using (var symmetricKey = new RijndaelManaged())

                    {

                        symmetricKey.BlockSize = 256;

                        symmetricKey.Mode = CipherMode.CBC;

                        symmetricKey.Padding = PaddingMode.PKCS7;

                        using (var decryptor = symmetricKey.CreateDecryptor(keyBytes, ivStringBytes))

                        {

                            using (var memoryStream = new MemoryStream(cipherTextBytes))

                            {

                                using (var cryptoStream = new CryptoStream(memoryStream, decryptor, CryptoStreamMode.Read))

                                {

                                    var plainTextBytes = new byte[cipherTextBytes.Length];

                                    var decryptedByteCount = cryptoStream.Read(plainTextBytes, 0, plainTextBytes.Length);

                                    memoryStream.Close();

                                    cryptoStream.Close();

                                    return Encoding.UTF8.GetString(plainTextBytes, 0, decryptedByteCount);

                                }

                            }

                        }

                    }

                }

            }

​

            private static byte[] Generate256BitsOfRandomEntropy()

            {

                var randomBytes = new byte[32]; // 32 Bytes will give us 256 bits.

                using (var rngCsp = new RNGCryptoServiceProvider())

                {

                    // Fill the array with cryptographically secure random bytes.

                    rngCsp.GetBytes(randomBytes);

                }

                return randomBytes;

            }

        }

        #endregion

}