  Key establishment is any process whereby a shared secret key becomes
available to two or more parties, for subsequent cryptographic use such as
symmetric-key encryption. Though it is widely known that the primitive of
encryption is different from key establishment, we find some researchers have
confused the two primitives. In this note, we shall clarify the fundamental
difference between the two primitives, and point out that the
Boneh-Gentry-Waters broadcast encryption scheme and its like are key
establishment schemes, not encryption schemes.
