Broadcast encryption
Broadcast encryption is the cryptographic problem of delivering content (e.g. TV programs or data on DVDs) over a 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.
Rather than directly encrypting the content for qualified users, broadcast encryption schemes that allows qualified users to reconstruct the content encryption key whereas revoked users find insufficient information to recover the key.
The problem of practical broadcast encryption has first been formally studied by and in 1994. A particularly efficient tree-based construction is the “subset difference” scheme, which is derived from a class of so-called subset cover schemes.