Decrypt an encrypted text

Question

I got a textbox and a 'decrypt' button in my Windows Form Application where I put an encrypted string in there and try to decrypt it but the problem is this. First, I got this class code called DataEncryptor from a guy on this website:

public class DataEncryptor
{
    TripleDESCryptoServiceProvider symm;

    #region Factory
    public DataEncryptor()
    {
        this.symm = new TripleDESCryptoServiceProvider();
        this.symm.Padding = PaddingMode.PKCS7;
    }
    public DataEncryptor(TripleDESCryptoServiceProvider keys)
    {
        this.symm = keys;
    }

    public DataEncryptor(byte[] key, byte[] iv)
    {
        this.symm = new TripleDESCryptoServiceProvider();
        this.symm.Padding = PaddingMode.PKCS7;
        this.symm.Key = key;
        this.symm.IV = iv;
    }

    #endregion

    #region Properties
    public TripleDESCryptoServiceProvider Algorithm
    {
        get { return symm; }
        set { symm = value; }
    }
    public byte[] Key
    {
        get { return symm.Key; }
        set { symm.Key = value; }
    }
    public byte[] IV
    {
        get { return symm.IV; }
        set { symm.IV = value; }
    }

    #endregion

    #region Crypto

    public byte[] Encrypt(byte[] data) { return Encrypt(data, data.Length); }
    public byte[] Encrypt(byte[] data, int length)
    {
        try
        {
            // Create a MemoryStream.
            var ms = new MemoryStream();

            // Create a CryptoStream using the MemoryStream 
            // and the passed key and initialization vector (IV).
            var cs = new CryptoStream(ms,
                symm.CreateEncryptor(symm.Key, symm.IV),
                CryptoStreamMode.Write);

            // Write the byte array to the crypto stream and flush it.
            cs.Write(data, 0, length);
            cs.FlushFinalBlock();

            // Get an array of bytes from the 
            // MemoryStream that holds the 
            // encrypted data.
            byte[] ret = ms.ToArray();

            // Close the streams.
            cs.Close();
            ms.Close();

            // Return the encrypted buffer.
            return ret;
        }
        catch (CryptographicException ex)
        {
            Console.WriteLine("A cryptographic error occured: {0}", ex.Message);
        }
        return null;
    }

    public string EncryptString(string text)
    {
        return Convert.ToBase64String(Encrypt(Encoding.UTF8.GetBytes(text)));
    }

    public byte[] Decrypt(byte[] data) { return Decrypt(data, data.Length); }
    public byte[] Decrypt(byte[] data, int length)
    {
        try
        {
            // Create a new MemoryStream using the passed 
            // array of encrypted data.
            MemoryStream ms = new MemoryStream(data);

            // Create a CryptoStream using the MemoryStream 
            // and the passed key and initialization vector (IV).
            CryptoStream cs = new CryptoStream(ms,
                symm.CreateDecryptor(symm.Key, symm.IV),
                CryptoStreamMode.Read);

            // Create buffer to hold the decrypted data.
            byte[] result = new byte[length];

            // Read the decrypted data out of the crypto stream
            // and place it into the temporary buffer.
            cs.Read(result, 0, result.Length);
            return result;
        }
        catch (CryptographicException ex)
        {
            Console.WriteLine("A cryptographic error occured: {0}", ex.Message);
        }
        return null;
    }

    public string DecryptString(string data)
    {
        return Encoding.UTF8.GetString(Decrypt(Convert.FromBase64String(data))).TrimEnd('\0');
    }

    #endregion

}

And he gave the usage of it:

string message="A very secret message here.";
DataEncryptor keys=new DataEncryptor();
string encr=keys.EncryptString(message);

// later
string actual=keys.DecryptString(encr);

I copied his code and works at encrypting and decrypting:

//my code
private void proceedED(string data)
{
    DataEncryptor key = new DataEncryptor();
    string encr = key.EncryptString(data);
    string actual = key.DecryptString(encr);
    encryptedLabel.Text = encr;
    decryptedLabel.Text = actual;     
}

Then I created a method like this:

private void proceedDecrypt(string data) 
{
    DataEncryptor key = new DataEncryptor();
    string decr = key.DecryptString(data);
    decryptedData.Text = decr;
}

The problem is that it crashes when I submit and I don't know why. I think it should be a true encrypted string because it's just a normal string. How do I fix this?

Answer 1

Each instance of DataEncryptor generates new keys. You need to use the same keys which encrypted the string to decrypt. If this is done in the same process then keep a reference to DataEncryptor key. Otherwise you need to initialize using the DataEncryptor(byte[] key, byte[] iv) constructor.

Try code like this:

class Program
{
    static void Main(string[] args)
    {
        string key, iv;

        var plain="A very secret message.";
        var cipher=EncryptString(plain, out key, out iv);

        // Later ...

        var message=DecryptString(cipher, key, iv);
    }

    public static string EncryptString(string plain, out string key, out string iv)
    {
        var crypto=new DataEncryptor();
        iv=Convert.ToBase64String(crypto.IV);
        key=Convert.ToBase64String(crypto.Key);
        return crypto.EncryptString(plain);
    }

    public static string DecryptString(string cipher, string key, string iv)
    {
        var crypto=new DataEncryptor(
            Convert.FromBase64String(key), 
            Convert.FromBase64String(iv));

        return crypto.DecryptString(cipher);
    }
}