## Homework 7 (due 2/28) CSC 233

Remember: next week your detailed sketches (for paper and presentation) are due.

We have finished talking about Polish break into the Enigma, and started talking about the work done in Bletchley Park, in particular Alan Turing's contribution. We will finish this part (how to build menus, and what they mean) next time before moving on to the key distribution problem, and public-key cryptography (chapter 6).

A detailed account of the history of rotor machines, and their cryptanalysis (with more material on the Enigma) is

Cipher A. Deavours, Louis Kruh. Machine Cryptography and Modern Cryptanalysis.

On the historical side, there is David Kahn's "Seizing the Enigma". It's coverage is similar to that of the movie.

1. [Enigma-Encryption] Your day settings are: 213, A/T P/Y, F/W, B/M, I/C, R/E, and rotor orientation RDY. Encrypt the message "Enigma Variations" using the method described on pages 147/148 of the book (i.e. you have to choose your own session key). (Hint:
use the enigma simulator we saw in class.)

2. [Enigma-Decryption] Your day settings are: 312, A/D, F/T, and rotor orientation VZS. You have received the signal

"KIQBE CTCLI DNKLZ TRKMD FCQK"

Decrypt (use the enigma simulator we saw in class). (Remember the use of session keys.)

3. (Crib) You intercepted the following ciphertext:

MNKCG LBHZA QEBBI HMKGP KFCST BMGGF RLEQH EAQOB PXDJX QMSWN
TSZTJ CSQLH QLGMM DZTWO ZL

You suspect it was encrypted using the enigma, and contains the crib "technicalpaper". What positions could the crib be at? Hint: to test whether a particular position is possible, remember that the Engima never encrypts a letter as itself. There will be several possible positions for the crib.

4. [Enigma] Explain, in your own words, the moral dilemma faced by the codebreakers in the movie Enigma (with respect to the convoy). Your explanation should be one or two paragraphs long, and should make clear the role of Shark, cribs, the short signal codebook and the weather codebook.

5. [Extra Credit] Finish problem P3.2 from the rotor cipher handout (you prepared for that with problem 5 on homework 6).

6. [Extra Credit] The move contains the line "The 3:00's from Beaumanor all need blisting.". Find out what "blisting" means (include a reference).

Marcus Schaefer
Last updated: February 21st, 2006.