Code and ciphers: Julius Caesar, the Enigma and the internet

6
Codes
Characteristics of codes
As was mentioned in Chapter 1, the distinction between codes and
ciphers is not always clear, but one might reasonably say that whereas
most codes tend to be static most ciphers are dynamic. That is to say that a
letter or phrase enciphered simply by means of a code will produce the
same cipher each time the code is used, whereas a letter or phrase enciphered
by a cipher system will generally produce different cipher text at
different times. This is because most cipher systems involve one or more
parameters, such as keywords or, as we shall see later, wheel settings,
which are changed at regular or irregular intervals and so cause the cipher
outputs from the same plaintext to be different. The basic mechanism, or
algorithm, for generating the cipher doesn’t change, but the parameters
do. In general, a code has no such parameters though the entire code may
itself be changed, in which case it becomes a different code. In practice
this is achieved by issuing a new code-book every now and then. Using
this criterion the Julius Caesar cipher would be classed as a code, because
the encipherment of a fixed letter across many messages is invariably the
same. We can, however, say that there is a parameter associated with
Julius Caesar ciphers, namely the shift, which gives us 25 different
ciphers and if the value of the shift is somehow incorporated in the
message, i.e. in the indicator, the Julius Caesar system can reasonably be
considered as a cipher, not as a code.
Example 6.1
Although there are much earlier examples of codes the one devised by
Samuel Morse (1791–1872) in 1832 for the purpose of transmitting messages
by telegraphy is probably the best-known. In this code the letters of
[64]