Most ciphers and especially the early ones had to easy to perform in the field. In particular it was dangerous to have the cryptosystem algorithms written down for the soldiers or spies to follow. Any cipher that was so complicated that its algorithm had to be written out was at risk of being revealed if the interceptor caught a sender with the written instructions. Then the interceptor could readily decode any cipher text messages intercepted. Sidebar 2-2 describes how the British dealt with written codes in world war11. the Caesar cipher is quite simple. During caesar’s lifetime, the simplicity did not dramatically compromise the safety of the encryption, because anything written, even in plaintext, was rather well protected. Its obvious pattern is also the major weakness of the Caesar cipher.