addressing and encrypted keys, were on the video lines that are recorded by normal VCRs and the data rate, unlike that of Teletext, was slow enough to allow the data to be recorded with the encrypted video. Decoder card datastream attacks The most successful hack on the VideoCrypt system is the "McCormac Hack" devised by John McCormac. This attack involved broadcasting the decryption keys from the decoder-card data live so that other decoders could use it to watch the encrypted channels, effectively sharing a card with several decoders. Card sharing is an implementation of the McCormac Hack. Brute force As desktop computing power increased, such a simple system was always inherently vulnerable to brute force 'image-processing' attacks. Even without any information at all about the cutpoint sequence, adjacent lines in a picture can be 'correlated' to find the best match, and the picture reconstructed. The Brute force method will not work for all pictures, but is an interesting proof-of-concept. Markus Kuhn's Antisky.c program from 1994 is an early example of such an attack. More recently it has been shown that, using detailed knowledge of the way colour is transmitted in analogue TV systems, 'perfect' reconstruction could be achieved for many scenes. Cheap PC TV cards (~£40) with particular chipsets (e.g.: Brooktree) were capable of descrambling the image in near real time (sound was delayed to match). This was made possible with software such as MoreTV or hVCPlus and a reasonably fast PC. The picture quality was on par with an old VHS videotape, with some colour distortion depending on PC performance. References John McCormac: European Scrambling Systems 5 – The Black Book, Waterford University Press, 1996, . Markus Kuhn: Attacks on pay-TV access control systems, seminar talk slides, 1997. Markus Kuhn: Some technical details about VideoCrypt, 1996. Markus Kuhn: AntiSky – an image processing attack on VideoCrypt, 1994. This C programme reassembles VideoCrypt encoded stills. Satellite television Digital rights management systems Television technology 1989 introductions Telecommunications-related introductions in 1989 Audiovisual introductions in 1989