cryptanalysts began by compiling a list of known classic codes and cipher methodologies
that can be used to encrypt secret messages. However, today powerful computers are used to
analyse the ciphertext and look out for certain keys used to encrypt (possibly several
times) the message.
None of these methods are guaranteed to work on the first try. Trial and errors are
common, but with experience, seasoned cryptographers could recognise certain patterns that
could provide some clue to the first step that should be taken.
When important messages are relayed, often unimaginative choice of words could give away
the encryption, as specialists in the field of cryptography have amassed a set of most
probable words as the nature of the message exhibits. For instance, in decoding love
letters, frequency ordering looks for words such as love, heart, fire, miss, life,
light which are most frequently used. Hence it is important to rephrase messages
before they are encrypted and transmitted.
Nothing can emphasize the importance of encrypting a message well. The slightest
carelessness may well reveal subsequent messages. However, not having code books does not
mean a message should be transmitted as plaintext. On the other hand, encrypted messages
containing obvious news, such as weather report on certain phenomenon that is most obvious
to the enemy, could prove to be a fatal leak.
Sometimes, the use of common phrase to describe a sudden, unforeseen event may give away
the encryption. This is exploited by the British in the World War II, when they
deliberately sank a lighted buoy in order to trigger certain predicted sequence in German
encrypted message, to assist decrypting.