解密时要解密的数据长度无效

Question

I need to encrypt an image, return the string of the encrypted data, then decrypt it

Here's my encryption code :

string plainText = ASCIIEncoding.ASCII.GetString(Imagebytes);
byte[] encrypted;
byte[] key = Encoding.UTF8.GetBytes("M02cnQ51Ji97vwT4");;
// Create an AesCryptoServiceProvider object 
using (AesCryptoServiceProvider aesAlg = new AesCryptoServiceProvider())
{
    aesAlg.Key = key;
    aesAlg.BlockSize = 128;

    // Create a decrytor to perform the stream transform.
    ICryptoTransform encryptor = aesAlg.CreateEncryptor(aesAlg.Key, aesAlg.IV);

    // Create the streams used for encryption. 
    using (MemoryStream msEncrypt = new MemoryStream())
    {
        using (CryptoStream csEncrypt = new CryptoStream(msEncrypt, encryptor, CryptoStreamMode.Write))
        {
            using (StreamWriter swEncrypt = new StreamWriter(csEncrypt))
            {

                //Write all data to the stream.
                swEncrypt.Write(plainText);
            }
            encrypted = msEncrypt.ToArray();

        }
    }
}

using (var aesAlg = new AesManaged())
{


    aesAlg.Key = new UTF8Encoding().GetBytes("M02cnQ51Ji97vwT4");
    aesAlg.IV = new byte[] { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 };
    ICryptoTransform encryptor = aesAlg.CreateEncryptor(aesAlg.Key, aesAlg.IV);

    return UTF8Encoding.UTF8.GetString(encryptor.TransformFinalBlock(Imagebytes, 0, Imagebytes.Length)).Length;

}

My decryption work fine ( because i can receive image / video perfectly )

here's the code:

const  string BLOB_KEY = "TTAyY25RNTFKaTk3dndUNA==";
using (RijndaelManaged rm = new RijndaelManaged())
{
    rm.Mode = CipherMode.ECB;
    rm.Key = Convert.FromBase64String(BLOB_KEY);
    rm.IV = new byte[] { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 };
    rm.Padding = PaddingMode.Zeros;
    using (MemoryStream ms = new MemoryStream())
    {
        using (CryptoStream cs = new CryptoStream(ms, rm.CreateDecryptor(),
                    CryptoStreamMode.Write))
        {
            cs.Write(image, 0, image.Length);
            return ms.ToArray();
        }
    }
}

What's wrong with my encryption code ?

Answer 1

Your very initial line of code is already wrong:

string plainText = ASCIIEncoding.ASCII.GetString(Imagebytes);

An image is not a string, and plaintext is not necessarily a string either. Both consist of bytes. So you should not be using a StreamWriter either, just a normal stream.

It is likely that data is lost during conversion.

Furthermore, you are writing to a decryption stream and you are using ECB mode at one side and CBC mode at the other.

I would strongly advice you to read into the material and start over.

Answer 2

Thank you, i've changed my code to :

var aesAlg = new AesManaged
        {
            KeySize = 128,
            Key = key,
            BlockSize = 128,
            Mode = CipherMode.ECB,
            Padding = PaddingMode.Zeros,
            IV = new byte[] { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 }
        };

        ICryptoTransform encryptor = aesAlg.CreateEncryptor(aesAlg.Key, aesAlg.IV);
        return encryptor.TransformFinalBlock(Imagebytes, 0, Imagebytes.Length);

And it works fine !