Another day in my life ... Alice, Bob and Marley have been introduced already. So a simple
question is still kept open: What is that stuff at all, you call crypto?
Well, thats not easy. Perhaps a very brief view back shold be done at first. From the greek
we know, they used some simple algorithm to prevent everybody from understanding their messages
sent by their personel. The usage of the scytale was simple: a leather band around a
cylinder was written longitudinal, the cylinder removed and then the leather band was "unreadable".
The receiver should have a cylinder of the same diameter. From wikipedia we know: It was mentioned
by Archilochus, who lived in the 7th century BC. A description of
how it operated is not known from before Plutarch (50-120 AD).
Today this procedure would not be assumed to be secure, because of a brute force attack using
different cylinders is easy.
The romans perhaps invented their caesar-cipher, named after Julius Gaius Caesar,
100 BC - 44 BC who is known to have used it. It is a linear substitution of letters,
f.e. 'c' for 'a', 'd' for 'b', 'e' for 'c' and so on.
This is best achieved by having two stripes with the same letters on them which are
misaligned for a constant number of letters. The reciever could test various numbers
for the reverse alignment or knows Caesars often used big secret: 3.
Some webbrowsers have implemented it in their menue: ROT13. Do it twice to have the
initial content. The big secret is the magic number 13. This just fits into the 26 letters
of our common alphabet.
These two examples for cryptographic methods are mentioned to show their usage in ancient
times. Whats about today?
Alice already said: History of cryptography is enriched by errors about the own knowledge.
And that is the truth, seen many times in the last 2000 years.
This little picture was taken on one of my trips to Munich in
the "Deutsches Museum München" from the 4-rotor enigma (marine version).
It's one of the best investigated crypto machines in history.
Thanks to Alan Turing and Marjan Rejewski.
Major flaw was the lack of randomness. ;-)