README

A simple simulation of an Enigma machine. You provide an encrypted message and
this will try all the different combinations of rotors, reflectors, and starting
positions to find the proper key. The messages and decrypes will be in ALL CAPS
with no spaces.

To determine which solution is correct this does a letter frequency analysis
and a digraph frequency analysis on the dycrypted message. Using the known
frequency of letters and digraphs in the English language, this assigns a score
to each decryption. The messages with the lowest scores are kept and displayed.
In my experiments, on a message of 80 characters is more than enough to make a
very good guess. Very short messages are much harder.

This was built using an Enigma simulator from
http://enigmaco.de/enigma/enigma.html as an oracle. The rotor mappings and
other information was taken from the Enigma and Enigma Rotor wikipedia pages.

http://en.wikipedia.org/wiki/Enigma_machine
http://en.wikipedia.org/wiki/Enigma_rotor_details

The letter frequencies used in the frequency analysis can be found in the
Letter frequency wikipedia article.
http://en.wikipedia.org/wiki/Letter_frequencies

To build use:
$ gradle clean test
$ gradle shadowJar

To run use:
$ java -jar build/libs/enigma-java-0.1-all.jar

The program takes a variety of arguments:
-message: Message is a required argument, it is the encrypted message to break.
-crib: If you have a crib, a known word in the decrypted message, you can
provide it to help identify the proper decoded message.
-rotors: The rotors to use. This should be a comma separated list. By default
the value is "1,2,3,4 5". If you know the message doesn't use rotor 4, then you
can reduce the number of combinations tried by changing rotors to "1,2,3,5".
-reflectors: Same as rotors, but which reflectors to use. By default this is
"A,B,C", but the simulator linked above only uses rotor B, so you can speed up
processing a lot by only specifying B.
-results: The number of results to display. By default this is 3.
-num_threads: The number of threads to use while processing. By default this is
8.

Some sample messages you can try are:
ZTQBLVXKPBPGAVQBRYDYQEZNKRLMZTMRGBJSQKHDPHHNTNIDLYVFCOKZYYSMJFAHQBTEAVFKOXRPSQX
which decrypts to
THISISASLIGHTLYLONGERTESTSOIHAVETOSEEIFICANKEEPWRITINGALONGERSTRINGTOUSEASINPUT
with KEY=AAB
Rotors: 1, 2, 3
Reflector: B

PCSONKFYSIQHZJCVFLPAWUWTXWYNWPTCCLOJNNKNCNECAAQPYNEWIFHVDZQIWYTXMEQQMZ
which decrypts to
IDONTREALLYKNOWWHATTHISMESSAGEISGOINGTOSAYBUTIMGOINGTOKEEPTYPINGANYWAY
with KEY=TJB
Rotors: 5, 1, 4
Reflector: B


MTVZLRUGJUPYISBINSDHPNXNJVYTX
which decrypts to
THISISASHORTMESSAGENOCRACKING
with KEY: TJB
Rotors: 3, 1, 4
Reflector: B
but only is you provide the crib SHORT