Rijndael decryption returns weird ouput

Question

I have used Rijndael Algorithm for Encryption and decryption.

The Decryption works fine when i do it with Encryption.

But when i try to do Decryption alone it returns something like this

J˿m"�e��c4�ħ�dB̵��Dq@W�.

Also i have used two buttons one is for encryption and another one is for decryption and called the methods when button clicks.

I cannot able to get any idea regarding why the output is returning like this. Even i used same convertion(UTF8 Encoding) for both methods.

Please help me to solve this problem.

Below is my code:

public partial class Form1 : Form
{
    private RijndaelManaged myRijndael = new RijndaelManaged();
    private int iterations;
    private byte [] salt;

    public Form1(string strPassword)
    {
        myRijndael.BlockSize = 128;
        myRijndael.KeySize = 128;
        myRijndael.IV = HexStringToByteArray("e84ad660c4721ae0e84ad660c4721ae0");

        myRijndael.Padding = PaddingMode.PKCS7;
        myRijndael.Mode = CipherMode.CBC;
        iterations = 1000;
        salt = System.Text.Encoding.UTF8.GetBytes("cryptography123example");
        myRijndael.Key = GenerateKey(strPassword);
    }

    public string Encrypt(string strPlainText)
    {
        byte[] strText = new System.Text.UTF8Encoding().GetBytes(strPlainText);
        MemoryStream ms = new MemoryStream();
        ICryptoTransform transform = myRijndael.CreateEncryptor();
        CryptoStream cs = new CryptoStream(ms, transform, CryptoStreamMode.Write); 
        cs.Write(strText, 0, strText.Length);

        cs.FlushFinalBlock();
        return Convert.ToBase64String(ms.ToArray());
    }

    public string Decrypt(string encryptedText)
    {
        var encryptedBytes = Convert.FromBase64String(encryptedText);
        MemoryStream ms = new MemoryStream();
        ICryptoTransform transform = myRijndael.CreateDecryptor();
        CryptoStream cs = new CryptoStream(ms, transform, CryptoStreamMode.Write);
        cs.Write(encryptedBytes, 0, encryptedBytes.Length);

        return System.Text.Encoding.UTF8.GetString(ms.ToArray());
    }

    public static byte[] HexStringToByteArray(string strHex)
    {
        dynamic r = new byte[strHex.Length / 2];
        for (int i = 0; i <= strHex.Length - 1; i += 2)
        {
            r[i / 2] = Convert.ToByte(Convert.ToInt32(strHex.Substring(i, 2), 16));
        }
        return r;
    }

    private byte[] GenerateKey(string strPassword)
    {
        Rfc2898DeriveBytes rfc2898 = new Rfc2898DeriveBytes(System.Text.Encoding.UTF8.GetBytes(strPassword), salt, iterations);
        return rfc2898.GetBytes(128 / 8);
    }

    private void button1_Click(object sender, EventArgs e)
    {
        EncryptOutput.Text = Encrypt(EncryptInput.Text);
    }

    private void button2_Click(object sender, EventArgs e)
    {
        DecryptOutput.Text = Decrypt(DecryptInput.Text);
    }
}

Answer 1

Try this code:

public string Encrypt(string strPlainText) {
    byte[] strText = System.Text.Encoding.UTF8.GetBytes(strPlainText);

    using (ICryptoTransform encryptor = myRijndael.CreateEncryptor())
    using (MemoryStream input = new MemoryStream(strText))
    using (MemoryStream output = new MemoryStream())
    using (CryptoStream cs = new CryptoStream(output, encryptor, CryptoStreamMode.Write)) {
        input.CopyTo(cs);
        cs.FlushFinalBlock();
        return Convert.ToBase64String(output.GetBuffer(), 0, (int)output.Length);
    }
}

public string Decrypt(string encryptedText) {
    byte[] encryptedBytes = Convert.FromBase64String(encryptedText);

    using (ICryptoTransform decryptor = myRijndael.CreateDecryptor())
    using (MemoryStream input = new MemoryStream(encryptedBytes))
    using (MemoryStream output = new MemoryStream())
    using (CryptoStream cs = new CryptoStream(input, decryptor, CryptoStreamMode.Read)) {
        cs.CopyTo(output);
        return System.Text.Encoding.UTF8.GetString(output.GetBuffer(), 0, (int)output.Length);
    }
}

public static byte[] HexStringToByteArray(string strHex) {
    var r = new byte[strHex.Length / 2];

    for (int i = 0; i < strHex.Length; i += 2) {
        r[i / 2] = byte.Parse(strHex.Substring(i, 2), NumberStyles.HexNumber);
    }
    return r;
}

Please, remember using the using pattern... And dynamic should be used only in very special cases.

Note that the Encrypt is doable with one less Stream, in a very similar way to the one you wrote it:

public string Encrypt(string strPlainText) {
    byte[] strText = System.Text.Encoding.UTF8.GetBytes(strPlainText);

    using (ICryptoTransform encryptor = myRijndael.CreateEncryptor())
    using (MemoryStream output = new MemoryStream())
    using (CryptoStream cs = new CryptoStream(output, encryptor, CryptoStreamMode.Write)) {
        cs.Write(strText, 0, strText.Length);
        cs.FlushFinalBlock();
        return Convert.ToBase64String(output.GetBuffer(), 0, (int)output.Length);
    }
}

but the Decrypt needs two Stream, because the CryptoStream needs a Stream as a parameter, containing the encrypted data, and it is easier to write its output (of which you don't know the exact lenth, thanks to padding) to another stream.

Answer 2

cs.FlushFinalBlock(); forgotten in Decrypt()? I just round-tripped a test string with your code once I fixed that