appropriate algorithm for application

[Cerridwyn Llewyellyn]

I need an algorithm/protocol that is capable of encrypting numerous
files with separate keys, but there also needs to be a master key
that will be able to decrypt all of them.  Is there such a system 
that is relatively secure?  I'd prefer the system to be as secure
as possible, but in this application, security is secondary to 
functionality.  Thanks... //cerridwyn//