AES-128-ECB解密：输入数据不是完整的块

Question

I am trying to write a code which would decrypt a text which was encrypted with AES-128-ECB and represented in Base64. The key is known (it's a task for educational purposes) and presented in ASCII (for example, YELLOW SUBMARINE).

Here is the code:

    private void button6_Click(object sender, EventArgs e)
    {
        string CTChar = Funcs.BitsToChar(Funcs.B64ToBits(textBox1.Text));
        Byte[] CTBytes = new Byte[CTChar.Length];
        for (int iCounter = 0; iCounter < CTChar.Length; iCounter++)
        {
            CTBytes[iCounter] = Convert.ToByte(CTChar[iCounter]%256);
        }
        string KeyBits = Funcs.CharToBits(textBox2.Text);
        Byte[] KeyBytes = new Byte[textBox2.TextLength];
        string PlainText = null;
        Aes Decryptor = Aes.Create();
        Decryptor.BlockSize = 128;
        for (int iCounter = 0; iCounter < textBox2.Text.Length; iCounter++)
        {
            KeyBytes[iCounter] = Convert.ToByte(textBox2.Text[iCounter]);
        }
        Decryptor.KeySize = textBox2.TextLength * 8;
        Decryptor.Key = KeyBytes;
        Decryptor.Mode = CipherMode.ECB;
        ICryptoTransform Decr = Decryptor.CreateDecryptor();

        using (MemoryStream msDecrypt = new MemoryStream(CTBytes))
        {
            using (CryptoStream csDecrypt = new CryptoStream(msDecrypt, Decr, CryptoStreamMode.Read))
            {
                using (StreamReader srDecrypt = new StreamReader(csDecrypt))
                {
                    PlainText = srDecrypt.ReadToEnd();
                }
            }
        }
        textBox3.Text = PlainText;
    }

When running it and trying to decrypt a text, an error occurs: The input data is not a complete block (Cryptographic Exception was unhandled). What am I doing wrong?

Answer 1

You should convert base 64 - which seems to be the format of the input ciphertext - directly to a Byte[]. You are currently converting it to bits, then to characters, then to bytes. Base 64 has been defined to encode bytes (or octets) to text.

Converting bytes with a random value to/from text will get you in trouble; it is one of the reasons why base 64 exists in the first place. Try and find a correct base 64 implementation for your platform, there should be plenty, even in the standard API.