Using these relationships, a cryptanalyst could reason from one to another and, potentially, derive a logical contradiction, in which case the rotor setting under consideration could be ruled out.
The basic principle of this sort of enciphering machine is that it should deliver a very long stream of transformations that are difficult for a cryptanalyst to predict.
The primary use of padding with classical ciphers is to prevent the cryptanalyst from using that predictability to find cribs that aid in breaking the encryption.
Although frequency analysis is a powerful and general technique against many ciphers, encryption has still often been effective in practice, as many a would-be cryptanalyst was unaware of the technique.
Provided the message is of reasonable length (see below), the cryptanalyst can deduce the probable meaning of the most common symbols by analyzing the frequency distribution of the ciphertextfrequency analysis.
Once a suitable crib had been decided upon, the cryptanalyst would produce a "menu" for wiring up the bombe to test the crib against the ciphertext.
The message settings should never have been re-used, but on occasion they were, providing a depth, which could be utilised by a cryptanalyst.
In classical cryptography a "null" is intended to confuse the cryptanalyst.
