C# Encrypt Text Output

Question

I have created a few little programs that export data to a text file using StreamWriter and then I read them back in using StreamReader. This works great and does what I nee

Answer 1

Just to add another implementation of Leon's answer, and following the Microsoft docs

Here a class example that encrypts and decrypts strings

    public static class EncryptionExample
{

    #region internal consts

    internal const string passPhrase = "pass";
    internal const string saltValue = "salt";
    internal const string hashAlgorithm = "MD5";
    internal const int passwordIterations = 3;             // can be any number
    internal const string initVector = "0123456789abcdf"; // must be 16 bytes
    internal const int keySize = 64;                      // can be 192 or 256

    #endregion

    #region public static Methods

    public static string Encrypt(string data)
    {
        string res = string.Empty;
        try
        {
            byte[] bytes = Encoding.ASCII.GetBytes(initVector);
            byte[] rgbSalt = Encoding.ASCII.GetBytes(saltValue);
            byte[] buffer = Encoding.UTF8.GetBytes(data);
            byte[] rgbKey = new PasswordDeriveBytes(passPhrase, rgbSalt, hashAlgorithm, passwordIterations).GetBytes(keySize / 8);
            RijndaelManaged managed = new RijndaelManaged();
            managed.Mode = CipherMode.CBC;
            ICryptoTransform transform = managed.CreateEncryptor(rgbKey, bytes);

            byte[] inArray = null;
            using (MemoryStream msEncrypt = new MemoryStream())
            {
                using (CryptoStream csEncrypt = new CryptoStream(msEncrypt, transform, CryptoStreamMode.Write))
                {
                    csEncrypt.Write(buffer, 0, buffer.Length);
                    csEncrypt.FlushFinalBlock();
                    inArray = msEncrypt.ToArray();
                    res = Convert.ToBase64String(inArray);
                }
            }
        }
        catch (Exception ex)
        {
            Console.WriteLine("Encrypt " + ex);
        }

        return res;
    }

    public static string Decrypt(string data)
    {
        string res = string.Empty;
        try
        {
            byte[] bytes = Encoding.ASCII.GetBytes(initVector);
            byte[] rgbSalt = Encoding.ASCII.GetBytes(saltValue);
            byte[] buffer = Convert.FromBase64String(data);
            byte[] rgbKey = new PasswordDeriveBytes(passPhrase, rgbSalt, hashAlgorithm, passwordIterations).GetBytes(keySize / 8);
            RijndaelManaged managed = new RijndaelManaged();
            managed.Mode = CipherMode.CBC;
            ICryptoTransform transform = managed.CreateDecryptor(rgbKey, bytes);

            using (MemoryStream msEncrypt = new MemoryStream(buffer))
            {
                using (CryptoStream csDecrypt = new CryptoStream(msEncrypt, transform, CryptoStreamMode.Read))
                {
                    using (StreamReader srDecrypt = new StreamReader(csDecrypt))
                    {
                        res = srDecrypt.ReadToEnd();
                    }
                }
            }
        }
        catch (Exception ex)
        {
           Console.WriteLine("Decrypt " + ex);
        }

        return res;
    }
}

By the way, here is the "salt value" definition that I had googled to find out what it was.

Salt value

If an attacker does not know the password, and is trying to guess it with a brute-force attack, then every password he tries has to be tried with each salt value. So, for a one-bit salt (0 or 1), this makes the encryption twice as hard to break in this way.