Split a byte array at a delimiter

Question

I\'m having a bit of an issue and, the other questions here didn\'t help me much.

I am a security student and I am trying to write a crypter for a project. For those

Answer 1

Your approach has a number of flaws - you're reading an entire Byte[] into memory, but decryption is a streamable process, so you're needlessly wasting memory. Secondly you cannot "split" an array (or a string, for that matter) in the CLR. When you split a CLR String it creates copies, which wastes memory.

Try this:

public static void Main(String[] args) {

    using(FileStream fs = new FileStream( @"path\to\fileName.exe", FileMode.Read)) {

        BinaryReader rdr = new BinaryReader( fs );
        SeekToEndOfDelimiter( rdr );

        // Use an implementation of RC4 decryption that accepts Streams as arguments, then pass fs directly as an argument:
        using(FileStream output = new FileStream( @"path\to\out.exe", FileMode.Write)) {
            // Providing the key arguments is an exercise for the reader
            MyRc4Implementation.DecryptStream( fs, output, key );
        }
    }

}

private static void SeekToEndOfDelimiter(BinaryReader rdr) {
    // Implementing this code is an exercise left up to the reader.
    // But just iterate through each byte (assuming ASCII-compatible encoding) until you encounter the end of the delimiter
}

There, no messy byte[] arrays :)