staple / unstaple
It gets more interesting if Bob wants to distribute Alice's content, A. Since he doesn't own the copyright, he probably can't do such distribution legally. Suppose Bob creates an archive file containing both A and B, the latter of which he owns the copyright to. He then runs staple 2 or staple 4 on the archive and publicly distributes it. Bob's friend, Charlie, who doesn't care about copyrights, runs unstaple, brute-forces the key, and recovers both A and B. Alice, however, is stuck. If she wants to prove that Bob is violating the DMCA, she must violate the DMCA herself since the only way for her to verify the contents of the stapled archive is for her to brute-force the key (thereby circumventing Bob's copyright protection mechanism) and recover its entire contents, which includes Bob's copyrighted file, B.
via Schneier on Security.
Using the RIAA/MPAA's weapons against themselves?