Blugh nobody wanted to play the game . So I will simply explain. If I have the following cipher text: -----BEGIN PGP MESSAGE----- Version: GnuPG v1.4.10 (GNU/Linux) hQEMAwRh9rcEwAqAAQf7BgY44mNJkmAyQZH6C52eCWP6PA7iC4cXM6ArH0hM974/ iwuBk5D/xmdj7C8R6HwR3MeNgdOKFmPN8ctuImkXdgSWUqKqf6X/JPGjtr5I6+JB lSzJrVNydGmQJ62gL8YZHR9spS/iLpXu4lrx6h1ZYOpdpZRWlGDFeMtEwW6zaK7o 03Cu00wx//ETDwGRZlrM8uSopSv+yy2LWGFpiKLnvSaHkUKIOi3DStPTHVfpVkL/ WoyvKQW2xC8a16kbrpr3buhzOlnhzrV/lXUULIPI2/SACa20DhJpQsTwXynrznY3 PLO2L5OOAZmP+yNu3SuKxXzuD7iqTqN3t5uu90vwZNJKAf39QBMn/NvT6alQjrTT rwipvq75UgpR3xL0ptmhUi/cgtD3CeiwESe2kgqhmDxJWpx74ymOkzSrm4LsT5ZL H2Z783xIxZZ1A6E= =1bIX -----END PGP MESSAGE----- which is sent from Alice to Bob, and Bob says the message decrypts into "kmf is a stupid fuck" when I ask him what the message is (Alice of course claims that it decrypts into "kmfw is awesome"), I can quickly prove that Bob is lying because the size of the ciphertext is 479 bytes (as it would be if the plaintext was "kmfw is awesome") and the ciphertext of "kmf is a stupid fuck" would have been 486 bytes. Of course I also need to know Bobs public key parameters. Also the message could very well have been "kmf is a fool!" ... but it certainly could not be "kmf is a stupid fuck" The moral of the story is that GPG ciphertexts don't disguise the size of GPG plaintexts. This could be very bad if you made an encryption system that only encrypts objects from a set. Even though an attacker can not break the encryption algorithm, they can still figure out what is going on. This is also the theory behind website fingerprinting attacks. An attacker could run an exit node and make a list of all of the websites accessed with it over a certain period of time. Then they could spider the websites visited. Then they could see the size of every page of a given website and the size of every page linked to off of that page. Then they could determine the size of every page linked to off of every page linked to from that page, etc. Now they can measure encrypted stream size at the entry node as their target surfs. Then they can use the process of elimination to determine the sites that the target is not visiting, and make a pretty good guess as to the site they are visiting (since the pattern will match and show that the target is potentially visiting that site, but certainly not visiting any of the sites for which their traffic pattern could not match). tl:dr : given a ciphertext encrypted to a known key, you can determine what the ciphertext will NOT decrypt into, and what it COULD decrypt into...but without breaking the encryption algorithm you can not determine what the ciphertext WILL decrypt into.