Cryptography

As I mentioned in class, you’ll need to read the first chapter of The Code Book for Monday. In case you’d like a little guidance for your reading or would like to prepare for Monday’s discussion, here are a few questions about Chapter 1 you might consider. I’m not expecting you to answer these questions (on the blog or in writing), I’m just providing them as a resource.

1. On page 41, Singh writes, “The cipher of Mary Queen of Scots clearly demonstrates that a weak encryption can be worse than no encryption at all.”  What does Singh mean by this and what does it imply for those who would attempt to keep their communications secret through cryptography?
2. Most of the examples of cryptography in Chapter 1 were associated with well-resourced people—monarchs, military leaders, etc.  Is that because those are the only examples that have survived or is that because cryptography and cryptography development is dependent on exceptional resources?  If the latter, do you think that has changed over time?  What implications does that have for today’s uses of cryptography?
3. Given that Singh was presumably trying to write an interesting and engaging book, why do you think he chose these examples for Chapter 1 instead of other potential examples of classical cryptography?

During our discussion of Singh Chapter 7, we’re going to focus on the security / privacy debate. However, here are a couple of questions on other topics to consider as you read the chapter.

1. Singh, writing around 1999, makes several predictions about the role of the Internet in our lives in the opening paragraph of Chapter 7. To what extent have these predictions come true? Are there other ways that the Information Age in which we now find ourselves has elevated the importance of encryption among the general public?
2. On page 315, Singh writes that Zimmerman, through a friend, “simply installed [PGP] on an American computer, which happened to be connected to the Internet. After that, a hostile regime may or may not have downloaded it.” In your opinion, do you think that someone who makes a piece of software available on the Internet should be held at least partially responsible for what criminals or foreign governments do with that software?

We’re focusing largely on the mathematical and technical material from Singh Chapter 6, but here are some reading questions that look at other aspects, in case they’re useful to you. We’ll defer discussion of the security / privacy debate until after Singh Chapter 7.

1. The National Security Agency made sure that the Data Encryption Standard (DES) was weak enough that the NSA could break it if necessary.  This, however, meant that businesses were forced to rely on security that was less than optimal.  Was the NSA justified in doing this?  Why or why not?
2. Singh writes on page 254, “[Whitfield] Diffie believed that if people then used their computers to exchange emails, they deserved the right to encrypt their messages in order to guarantee their privacy.”  Do you agree that private citizens have a right to have access to secure encryption technologies?
3. Who invented public key cryptography-the GCHQ researchers Ellis, Cocks, and Williamson or the academic researchers Diffie, Hellman, Merkle, Rivest, Shamir, and Adleman?
4. This chapter included discussion of several different mathematical aspects of modern cryptography.  What was one mathematical idea in this chapter that made sense to you?  What was one that didn’t make sense to you?

We’ll start discussing Singh Chapter 4 on the Monday after fall break. Here are some questions to guide your reading. Look for a blog post assignment about World War II cryptography soon.

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?

I just realized I never shared reading questions for Singh Chapter 3. Here they are, in case they’re still useful. Reading questions for Chapter 4 are coming right up.

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?
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?

Here are a few questions about Singh Chapter 2 you might consider as you read.

1. For some time before the development of the Vigenère cipher, “anybody sending an encrypted message had to accept that an expert enemy codebreaker might intercept and decipher their most precious secrets.” (Singh, p. 45)  How is this environment different from the one that Mary Queen of Scots experienced, where one didn’t know how likely it was that one’s encrypted message was secure?
2. The Great Cipher used by Louis XIV remained unbroken for 200 years.  What were the factors that led to such a secure cipher?
3. Why do you think that the advent of the telegraph motivated the use of a more secure cipher like the Vigenère cipher?
4. Prior to the work of Babbage and Kisiki, “most cryptanalysts had given up all hope of ever breaking the Vigenère cipher.”  Given that the Vigenère cipher was well-known, what might lead a cryptanalyst of that time to give up hope in cracking it?
5. Singh notes that in the latter half of the 19^th century, there was “an enormous growth of interest in ciphers among the general public.” (p. 79)  What factors do you think led to this growth?  Would you say there is interest in ciphers among the general public today?
6. The Beale Ciphers have remained unbroken for over a hundred years.  Given that hundreds if not thousands of professional and amateur cryptanalysts have tried to break them without success, why do you think there are still people who attempt to break them?  What motivates people like that?

I meant to post this on Friday, but just in case it’s still useful…

Here are a few questions about Singh Chapter 1 you might consider. I’m not expecting you to answer these questions (on the blog or in writing), I’m just providing them as a resource.

1. On page 41, Singh writes, “The cipher of Mary Queen of Scots clearly demonstrates that a weak encryption can be worse than no encryption at all.”  What does Singh mean by this and what does it imply for those who would attempt to keep their communications secret through cryptography?
2. On page 15 of The Code Book, author Simon Singh writes, “Cryptanalysis could not be invented until a civilization had reached a sufficiently sophisticated level of scholarship in several disciplines, including mathematics, statistics, and linguistics.”  If such a level of scholarship was required for the development of the frequency analysis approach to solving substitution ciphers, what do you make of the fact that amateur cryptanalysts today often use that approach “on their own,” so to speak, without being trained in it?
3. Most of the examples of cryptography in Chapter 1 were associated with well-resourced people—monarchs, military leaders, etc.  Is that because those are the only examples that have survived or is that because cryptography and cryptography development is dependent on exceptional resources?  If the latter, do you think that has changed over time?  What implications does that have for today’s uses of cryptography?
4. Given that Singh was presumably trying to write an interesting and engaging book, why do you think he chose these examples for Chapter 1 instead of other potential examples of classical cryptography?