CSharp和Golang之间的AES-CFB实现不一致

Question

I'm not able to decrypt a string encrypted with CSharp using Golang, because I think CSharp uses a CFB8 and Golang CFB128 (Feedback Size). But if I use CSharp with FeedbackSize=128 then I need to use Padding that as a result I will have it also in the encrypted text (that Golang doesn't have), viceversa I cannot use FeedbackSize=8 in Golang because is not implemented.

Any idea?

CSharp code:

static void Main(string[] args)
    {
        byte[] msg = Encoding.UTF8.GetBytes("Message to encrypt");
        byte[] k = Encoding.UTF8.GetBytes("0123456789abcdef");
        byte[] iv = Encoding.UTF8.GetBytes("0123456789abcdef");
        using (RijndaelManaged Aes128 = new RijndaelManaged())
        {
            Aes128.BlockSize = 128;
            Aes128.KeySize = 128;
            Aes128.Mode = CipherMode.CFB;
            Aes128.FeedbackSize = 8;
            Aes128.Padding = PaddingMode.Zeros;
            Aes128.Key = k;
            Aes128.IV = iv;

            using (var encryptor = Aes128.CreateEncryptor())
            using (var msEncrypt = new MemoryStream())
            using (var csEncrypt = new CryptoStream(msEncrypt, encryptor, CryptoStreamMode.Write))

            using (var bw = new BinaryWriter(csEncrypt, Encoding.UTF8))
            {
                bw.Write(msg);
                bw.Close();
                msg = msEncrypt.ToArray();
                Console.WriteLine("Encrypted " + BitConverter.ToString(msg));
            }
        }
    }

Result:

Encrypted 3F-D6-AD-8E-D5-34-E6-2D-38-7B-38-4E-DE-72-E8-B1-42-1C

Golang code:

    package main
import (
    "crypto/aes"
    "crypto/cipher"
    "fmt"
)
func main() {
    msg := []byte("Message to encrypt")
    k := []byte("0123456789abcdef")
    iv := []byte("0123456789abcdef")
    {
        block, _ := aes.NewCipher(k)
        stream := cipher.NewCFBEncrypter(block, iv)
        stream.XORKeyStream(msg, msg)
        fmt.Printf("Encrypted %x
", msg)
    }
}

Result:

Encrypted 3f170dfb7fbb982174c8380d176ac71c89ac

Note: if I change to Aes128.FeedbackSize = 128, then I got an error because I don't use padding, if I use padding I have the following result:

Encrypted 3F-17-0D-FB-7F-BB-98-21-74-C8-38-0D-17-6A-C7-1C-89-AC-F2-4F-9A-1D-E8-0B-D4-40-21-60-AF-48-36-5F

Many thanks in advance.

Answer 1

CFB should not require padding, but you can always implement it in GoLang to get around the stupidity of the RijndaelManaged implementation. Just apply the padding before encryption and the unpadding after decryption. The .NET library uses PKCS#7 padding by default.