Hiding secrets behind the law – DRM, AACS and the 16-byte key

It surprises and annoys me when I hear of individuals or companies trying to use the law to hide secrets. Surprise at the sheer stupidity and annoyance that tax payers money is used in the process.

The latest secret under suppression is a short 16-byte key which locks away the content on HD-DVD discs that only licensed software and hardware can play it back and prevent you from making copies.

This type of protection used to be called copy-protection but these days it goes under the equally unpopular name of "Digital Rights Management (DRM)". It enforce the copyright holders rights whilst denying you yours and does it in such a way that in some countries re-asserting your legal rights means you end up breaking others.

The AACS Licensing Authority believe they can now protect by law what they failed to protect using technology. This is particularly amusing because their predecessor, the DVD-CCA, failed on both counts when the encryption on DVD was broken in 1999 by an enterprising trio. Apple gets it and is going down the DRM-free route and not treating their customers like criminals.

Basing an entire business model on keeping a sequence of characters secret defies belief and thinking you can wipe the secret off the face of the internet once it’s out is laughable especially when you consider the infinite number of ways you could represent it. The AACS are at it anyway with take down notices to the likes of Digg and others. Amusingly the take down notice itself includes the ‘magic key’.

Alternative 16-byte sequence where each byte is an offset on the previous one is "09 F0 18 F1 9B D7 6F 78 7D 69 15 6F 9E F3 32 38" which if run through the following program yields a certain magic key.

class Program {
  static void Main(string[] argv) {
    byte b = 0;
    string key = string.Empty;
    foreach(string a in argv) {
      b += byte.Parse(a, System.Globalization.NumberStyles.HexNumber);
      key += string.Format("{0:x2} ", b);
    }
    System.Console.WriteLine(key);
  }
}

[)amien