Everyone has this problem, not just Apple. There are counterfeit (and re-worked) every-things which sometimes leads to bad endings (i.e. using my imagination, exploding batteries come to mind). When I was asked to deal with this problem we used SHA1 and HMAC encoding. We would challenge our selves and the UnitUnderTest. If the returned hash from the UnitUnderTest (untrusted) and our selves (trusted) matched, then we would trust the "untrused" UnitUnderTest. In the case of and iPod, it would then play back the video.

If implemented well, I doubt you will find it easy to break (find the hidden key). It would be much easier just to buy the cable.

BTW, if you upgrade the FW on (some?/all?) old iPods you probably will pick up this "no video until validated" feature.

BTW, don't go and buy old iPod video stuff off of ebay until you know you are getting something that will authenticate. Plenty of after market non-authorizing video players went for *very* low (like $30) prices several years ago when Apple introduced this feature. Bad news for Apple owners, but a windfall for us hackers!

If the cable used to work before, it should still work for the new one. Jailbreak and get this app: http://iphonehelp.in/2009/01/20/tvout-via-cydia-view-your-iphone-screen-on-tv-apps-media-games/

The new ipods require an authentication chip to enable video output. I advise buying a cheap cable from dealextreme with the chip embedded already. I suppose you could reverse engineer the signals sent to the ipod and make your own with a micro, but that would still require you to buy a cable to test with. Ironically, if you connect the authentication cable when the video starts playing, and then switch to the old four pin headphone video adapter without authentication chip, the ipod will continue to output video. This mean that the ipod only checks for the chip when it starts outputting video. Luckily I have a 5th gen ipod and don't have to worry about all this, but Apple really dropped the ball with the authentication chip nonsense.