AES Negative bytes | 易学教程

问题

The following is an extract from using AES encryption in Java:

  encryptedData =   encryptCipher.doFinal(strToEncrypt.getBytes());

The following is an extract in c#

 DecryptStringFromBytes_Aes(encrypted, myAes.Key, myAes.IV);

Both use a byte array one to encrypt the other to decrypt, the encryption in Java encrypts producing some negative values stored in a byte array.

C# uses a byte array to decrypt but a byte in C# is defined as only containing the numbers from 0..255 - Java defines its Byte type as -128 to 127.

Therefore, I cannot send encrypted data to the remote application which is written in C# because it cannot decrypt using the byte array that has been sent from the Java aplication.

Has anyone come up with a solution that would allow me to tell java not to produce negative numbers when encrypting?

The code is from Micrsoft, the MemoryStream requires the byte[] to create the stream for the crypto code... As mentioned or not, I replaced byte[] with sbyte but to no avail as MemoryStream requires byte[]

static string DecryptStringFromBytes_Aes(sbyte[] 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 Aes object 
        // with the specified key and IV. 
        using (Aes aesAlg = Aes.Create())
        {
            aesAlg.Key = Key;
            aesAlg.IV = IV;

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

            // Create the streams used for decryption. 
            using (MemoryStream msDecrypt = new MemoryStream((byte)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;


    }

回答1:

Java's bytes are signed, C# bytes are unsigned (there's also an sbyte type in C#, that no one uses, which works like Java's bytes).

It doesn't matter. They are different in some regards, namely

when converted to int, C#'s bytes will be zero-extended, Java's bytes will be sign-extended (which is why you almost always see & 0xFF when bytes are used in Java).
when converted to string, Java's bytes will have their 128 - 255 range mapped to -128 - -1. Just ignore that.

The actual value of those bytes (that is, their bit-pattern) is what actually matters, a byte that is 0xAA will be 0xAA regardless of whether you interpret it as 170 (as in C#) or -86 (as in Java). It's the same thing, just a different way to print it as string.

new MemoryStream((byte)cipherText)) definitely doesn't do the right thing (or anything, it shouldn't even compile). The related new MemoryStream((byte[])cipherText)) wouldn't work either, you can't cast between primitive arrays like that. cipherText should just be a byte[] to begin with.

回答2:

You could turn it into a string with some encoding, like:

encryptedData =   encryptCipher.doFinal(strToEncrypt.getBytes());
String s = new String(encryptedData, "Base-64");

Using the same standardized encoding, both C# and Java should be able to reconstruct each others encrypted data from that string.

来源：https://stackoverflow.com/questions/23079047/aes-negative-bytes

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