months later, they finally broke their silence after it became clear that the Internet was piecing things together. Why didn't WikiLeaks simply set the encrypted file to expire after a certain period of time? This is one of the most common criticisms. Many technical people have stated: "PGP lets you set keys to expire at a certain date. Assange could have used that technology." It isn't true. In fact, if you have such technology, Microsoft, Sony and the MPAA would love to hear from you, because that would be the holy grail of DRM technology. You can't make bits that "expire" or "self-destruct" -- they are infinitely copyable and don't disappear unless every single person who has a copy of them simultaneously and voluntarily deletes them. That tends not to happen. When people say "PGP lets keys expire," they're thinking of signatures , not encryption. PGP has two main uses: signing files ("is this file really from the person who claims to be its author?") and encrypting files ("nobody can read this file except its intended recipient"). On the opposite side, you can verify a signature or decrypt a file. When verifying a signature, it is in the client (the one verifying the file)'s best interests to fail if there is any doubt, so the client will first check that the signature is valid, and then check that the key's expiration date is in the future compared to the computer's clock. You could set your computer's clock back if you