[Spooks] New question on NS

[Gian Romani]

Hi everybody, this is my new question: a lot of trasmissions have similar
structure. Why the whole message is generally divided in 5 letters (or 5
numbers) groups? Or sometimes 4 letters/numbers? Is it just for practical
reasons, because 5 letters or 5 numbers are the ideal format to listen to
and write? Maybe longer structures affects readability and cause
transcription errors due to misunderstanding and lack of concentration? Are
there other reasons? Since most messages have same structures it means that
to be prepared (i.e. to encrypt the clear text) is used the same method:
why? Why don't eachone use a different method? To encrypt these messages I
think a software is used: after all this time and all those messages sent
and received, does some information about that has ever came out? Does
anyone has info or suspects for that? Is there any software useful to try
to decrypt this structure?
thank you, bye
Naig