Not necessarily, because some ciphers retain statistical information about the plaintext . any prior knowledge about the shape of the plaintext can give you better than flat random chance of recognizing he decrypt.
Re:Can you crack a code?
by youngerdryas on Friday May 03, 2013 @09:31AM
(#5650005)
A one time pad cipher can be considered unbreakable.
Wouldn't a single message from an unknown cipher be almost impossible to crack? You'd either need to know the algorithm or have multiple encoded messages along with the keys, right?