Cryptography

The History and Mathematics of Codes and Code Breaking

Month: October 2010

Class Participation Grading Scheme

Here's the class participation grading scheme I described in class today:

  • There will be 9 sets of pre-class reading questions this fall. The percentage of these that you respond to will be your PCRQ score.
  • I'll take the number of bookmarks you post to Delicious and divide by 10 to get your Delicious score. Note that I'll cap this at 120%, so that if you bookmark 12 or more sites on Delicious, you'll get a 120% for this score. All Delicious bookmarks are due by midnight on December 2nd.
  • Same thing for the timeline: I'll take the number of your contributions and divide by 10 to get your timeline score.  This score also has a cap of 120%, and the timeline deadline is midnight on December 2nd.

Then I'll add your three scores and divide by 200, capping the result at 100%.  This will be your overall class participation grade, which contributes 15% of your grade in the course. Let me know if you have any questions about this.

Image: "Numbers..." by Flickr user Luis Argerich, Creative Commons licensed.

Problem Set 5

Here's Problem Set 5: Word and PDF.  It's due on Tuesday, November 9th, Thursday, November 11th.

Reading Questions for October 26th

In preparation for class on Tuesday, October 26th, please read through page 201 in Chapter 5 of the Singh book and respond to the following questions.

  1. As we end our reading on military cryptography, what do you now say to the question of the importance of cryptography in World War Two?  To what extent was cryptography the decisive element of military victories?  Bear in mind Admiral Chester Nimitz’s quote on page 191 and Major General Howard Conner’s quote on page 200.
  2. Given the United States’ poor treatment of Native Americans over the years, what might motivate young Navajo men to join the Marines during World War Two?  What social challenges do you think they faced while serving in the Marines?
  3. Why have we not read much thus far about contributions of women to cryptography? Why does Singh limit his discussion of women at Bletchley Park to one sentence on page 161?
  4. What examples have you seen thus far of the work of cryptographers and cryptanalysts not getting the credit it was perhaps due? Is it important to give accurate credit to groundbreaking work in cryptography, mathematics, or science? Why?
9 Comments

Resources from October 12th and 19th - Zimmerman Telegram, Enigma Machine

  • PowerPoint Slides from the 12th [PDF] - Including an example of the use of the ADFGVX cipher and some thoughts on the ethics of Admiral's Hall decision to delay telling the United States about the Zimmerman Telegram
  • Trailer for Enigma (2001):

Reading Questions for October 21st

In preparation for class on Thursday, October 21st, please read the fourth chapter in the Singh book and respond to the following questions.

  1. Given what you’ve now read about Bletchley Park’s role in World War Two, would you say that “Bletchley Park’s achievements were the decisive factor in the Allied victory”?
  2. Why might the Germans increase the number of scramblers and plugboard cables in their Enigma machines to make them more secure, yet also insist that the Enigma cipher could not possibly be broken by the Allies?
  3. We’ve seen that the Vigenère cipher was once though unbreakable but later broken.  Given that history, why might the Americans and French conclude that the Enigma cipher was unbreakable prior to the start of the Second World War?
  4. Singh writes on page 149 that “the creative codebreaker must ‘perforce commune daily with dark spirits to accomplish his feats of mental ju-jitsu.’”  In light of your own experiences breaking ciphers, which is more important to successful codebreaking-logic or creativity?  Or is an equal balance of both required?
  5. The Timeline: Take a look at the crpytography timeline you've built as a class. What insights about the history of cryptography occur to you as you examine the timeline? How could the timeline be improved to make it more useful to you, particularly as you think ahead to your "big questions" paper at the end of the course?
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Essay #2 - Expository Paper

You may not be finished with your revisions to your opinion paper, but I wanted to go ahead and give you the assignment for your second essay, the expository paper, in case you have time to get started on it. Here's the assignment and the grading rubric. I'll take questions on this assignment in class tomorrow.

Reading Questions for October 12th

In preparation for class on Tuesday, October 12th, please read the third chapter in the Singh book and respond to the following questions.

  1. When the Zimmerman telegram was deciphered by the cryptanalysts of Britain’s Room 40, Admiral William Hall decided not to tell American President Woodrow Wilson about its contents because doing so might let the Germans know that Britain was capable of breaking their codes.  Given the danger posed to America by the unrestricted U-boat warfare indicated in the telegram, was this ethical of Admiral Hall? (For those of you who responded to this question in your first essay, please don't cut-and-paste your essay here...)
  2. Germany learned that Britain had broken their codes from histories of the First World War written by Winston Churchill and the British Royal Navy.  Given that this knowledge prompted Germany to invest in the Enigma machine technology prior to the Second World War, should these histories have been published?  What might have motivated Britain to make their code-breaking success known in this fashion?
  3. Given the various incidents recounted in this chapter, what are some conditions that seem favorable to the advancement of military cryptography?
  4. Singh’s examples of breaking difficult codes (such as the example beginning on page 116 about a keyword as long as the plaintext) seem to make breaking such codes (relatively) straightforward.  Why are these codes so much more difficult to break in practice, as you’ve seen on recent problem sets?
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Essay #1 Revisions

As I mentioned in class yesterday, I'm asking you to revise your opinion essay and submit your revised essay to me by the start of class on Tuesday, October 19th (the Tuesday after Fall Break).

The Writing Studio activities we used in class yesterday--the memory draft, the reverse outline, and the four optional activities--should be useful as you revise. Here's a PDF of the handout describing those activities. You also have my comments on your papers to guide you.

I'll grade your revised paper using the same rubric I used for your first paper, then I'll average your two grades to get your final grade on this essay. If you don't significantly revise your paper, I'll instead take 10 points off your first grade.

If you'd like some help with your revision, feel free to stop by my office hours or schedule an appointment with me. As I said in class, you all did pretty good on these papers, but I think with some revision, you have the potential to have some really great papers.

Image: "pen and paper" by Flickr user LucasTheExperience, Creative Commons licensed.

Resources from October 5th - Unsolved Mysteries, Probability Rules

Unsolved Mysteries

  • Here's the Wired Magazine article on Kryptos: "Mission Impossible: The Code Even the CIA Can't Crack," Steven Levy, April 2009.
  • James Sanborn has another interesting cryptography sculpture call the Cyrillic Projector. Below you can see a video project one of my former students did on this second sculpture.

Probability and Combinatorics

Image: "Antipodes" by Flickr user Fotomoe, Creative Commons licensed.

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