The value of a cypher is more than just its resistance to being deciphered. Professional codes must be able to efficiently transmit enormous amounts of information and be deciphered unambiguously and quickly, usually by automated methods. Any element of randomness or whimsy usually defeats the codebreaker but it also makes the cypher less useful for real intelligence or military use.

Amateur codes can be fundamentally impossible to break, because they are often based on totally random sequences, or look up tables that both sides must have in their possession ("The Key to Rebecca"). Of course, the most effective code of all is the one that consists of a message that carries no information at all. It is pure gibberish masquerading as espionage. Their purpose is not to convey information to an ally, but to confound and demoralize the enemy and force him to consume resources in a futile attempt to break it.