Read a file and decrypt it to memory stream object

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I'm using this function to Decrypt a string (or better a Bytes[])

    static string DecryptStringFromBytes(byte[] cipherText, byte[] Key, byte[] IV)
    {
        // Check arguments.
        if (cipherText == null || cipherText.Length <= 0)
            throw new ArgumentNullException("cipherText");
        if (Key == null || Key.Length <= 0)
            throw new ArgumentNullException("Key");
        if (IV == null || IV.Length <= 0)
            throw new ArgumentNullException("Key");

        // Declare the string used to hold
        // the decrypted text.
        string plaintext = null;

        // Create an Rijndael object
        // with the specified key and IV.
        using (Rijndael rijAlg = Rijndael.Create())
        {
            rijAlg.Key = Key;
            rijAlg.IV = IV;

            // Create a decrytor to perform the stream transform.
            ICryptoTransform decryptor = rijAlg.CreateDecryptor(rijAlg.Key, rijAlg.IV);

            // Create the streams used for decryption.
            using (MemoryStream msDecrypt = new MemoryStream(cipherText))
            {
                using (CryptoStream csDecrypt = new CryptoStream(msDecrypt, decryptor, CryptoStreamMode.Read))
                {
                    using (StreamReader srDecrypt = new StreamReader(csDecrypt))
                    {

                        // Read the decrypted bytes from the decrypting stream
                        // and place them in a string.
                        plaintext = srDecrypt.ReadToEnd();
                    }
                }
            }

        }
        return plaintext;
    }

And i call it with this code:

    private void button3_Click(object sender, EventArgs e)
    {

        using (Rijndael myRijndael = Rijndael.Create())
        {
        using (MemoryStream msEncrypted = new MemoryStream())
        using (FileStream file = new FileStream("file.bin", FileMode.Open, FileAccess.Read))
        {
            byte[] bytes = new byte[file.Length];
            file.Read(bytes, 0, (int)file.Length);
            msEncrypted.Write(bytes, 0, (int)file.Length);
            string roundtrip = DecryptStringFromBytes(bytes, myRijndael.Key, myRijndael.IV);
            textBox2.Text = roundtrip;
        }

        }         
    }

But it throw an exeption: plaintext = srDecrypt.ReadToEnd();

An unhandled exception of type 'System.Security.Cryptography.CryptographicException' occurred in mscorlib.dll

asked 34 secs ago

Stefano Camaiani

3

Read a file and decrypt it to memory stream object