Broadcast encryption is the cryptographic problem of delivering encrypted content (e.g. TV programs or data on DVDs) over a broadcast channel in such a way that only qualified users (e.g. subscribers who have paid their fees or DVD players conforming to a specification) can decrypt the content.
[7] The problem of practical broadcast encryption has first been formally studied by Amos Fiat and Moni Naor in 1994.
Luby and Staddon have used a combinatorial approach to study the trade-offs for some general classes of broadcast encryption algorithms.
[4] The subset difference scheme is notably implemented in the AACS for HD DVD and Blu-ray Disc encryption.
[8][4] In practice, pay TV systems often employ set-top boxes with tamper-resistant smart cards that impose physical restraints on a user learning their own decryption keys.