Canal+’s 1984 analog TV encryption shifted each scanline right by 0, 13, or 26 pixels using an 11-bit LFSR key, defeated by leaked schematics within months.
Key Takeaways
Discret 11 operated entirely in the analog domain: a cheap hardware delay chip (TBA 970) shifted each of 576 scanlines using LFSR output mod 3, no digital processing needed.
The 11-bit key was not entered directly; subscribers typed an 8-digit code hashed with their decoder’s serial number, producing six 11-bit keys for tiered audience levels (Cinema, Sports, etc.).
Synchronization relied on lines 310 and 622 blinking black or white; line 622 also encoded the audience tier. The LFSR reset every 6 frames.
Audio got far less protection: AM modulation at 12.8 kHz with band inversion, no key, fully reversible by anyone with the circuit knowledge.
By December 1984, Radio Plans magazine was legally blocked from publishing schematics but the drawings leaked anyway; asking for a TBA 970 in any electronics shop became code for a full pirate decoder parts list.
Hacker News Comment Review
The single comment zeroed in on the Easter egg buried in the spec: the month-end “free mode” fallback key hardcoded into every decoder was 1337, a deliberate leet-speak in-joke by the engineers.
No broader technical debate on LFSR design, SECAM signal structure, or the Nagravision migration that replaced Discret 11 in 1992.
Notable Comments
@dtagames: “The ‘all free’ code was 1337 or ‘leet’ in leet!” – engineers baked the Easter egg into the free-access fallback key used during subscription transition days.