[GreenKeys] Cryptography

[jhhaynes at earthlink.net]

The Vernam cipher goes back to 1917 or so and consists of a key
generator which generates 5-bit patterns that are exclusive-ORed
with the five bits in the TTY tape to generate the cipher text.
And then the received tape is run through a similar item to get
back to clear text.  One version of key generator used three tape
loops of different lengths, so it took a long time to repeat the
pattern.  As I recall William Friedman was able to break this
encryption.  The other version where a single one-time tape is used
as a key is unbreakable if the tape is truly random.  The problem
with this is that you need as many characters of key as there are
of text to be transmitted.

Teletype manufactured crypto equipment, not all of which was used
online.  The SIGABA was the principal high-level machine of World
War II and later, and was an offline machine.  I've read there was
also some arrangement where it could be used online.

There is an Army TM - I don't have the number handy, but the title is
something like "Receiving Transmitter Distributors" and it shows
machines that look like the ordinary Model 14 XD, but the faceplate
distributor is different, having narrow segments to sample the
bits as they are being processed.  This is an unclassified publication,
as the box that generated the key is not described therein.

There is a book, The Story of MAGIC by Frank B. Rowlett that, as I
recall, describes another machine made by Teletype for online crypto
use.

There was of course the German cryptography based on Baudot teleprinter
technology and broken by the English.  The Geheimschreiber by Siemens
and the Sz40 and Sz42 machines made by Lorenz.

There is a little bit of literature about cryptography for non-military
use.



jhhaynes at earthlink dot net