The History and Mathematics of Codes and Code Breaking

Category: Resources (Page 1 of 4)

The Ethics of Military Cryptography

We ran out of time at the end of class today to wrap up our discussion of the ethics of military cryptography. Sorry about that! I think our in-class activity worked well, but it needed a bit of discussion at the end. In lieu of that discussion, I'll share a few more perspectives on the Zimmerman telegram debate here on the blog.

Claim: Admiral Hall's decision to withhold information from the Americans about the Zimmerman telegram was ethical.

  • In the short run, telling the Americans would have saved lives, but maintaining the ability to decipher German messages would save more lives in the long run.
  • Hall's first responsibility was to his own country, and that country--and its whole way of life--was at risk from German invasion.  That was a bigger risk than the Americans faced, and a more immediate risk.
  • Who were the real bad guys here? It was the Germans who were attacking ships. It was the Germans who were lying to the Americans.
  • The Americans, as it turned out, were going to drag their feet anyway.  Telling them wouldn't have brought them into the war any earlier, and it might have compromised British cryptography efforts.

Claim: Admiral Hall's decision to withhold information from the Americans about the Zimmerman telegram was NOT ethical.

  • By not telling the Americans, people definitely died. Had the British told the Americans and the Germans realized their codes were broken, more lives might have been lost in the long run—but, in the short run, people definitely died.
  • What England did was as unethical as what Germany did—manipulating the Americans for their own ends.
  • Britain wanted America as an ally, which is a trust-based relationship. Hall was keeping secrets from the American government and undermining the trust between the nations.
  • Hall could have justified his decision by saying that he was doing what was, in his mind, best for America. However, that wasn't his place--it was the responsibility of the American government to make such decisions.
  • Didn’t Hall plan to let the submarine warfare happen so that America would be prompted into war? Dragging more people into a conflict is only going to result in more deaths.

Keep in mind that, in an effort to tell engaging and accessible stories, the author sometimes omits some of the complexities of the issues he discusses. As you read, consider ways that you can approach these issues from multiple perspectives.

Welcome to Class!

I'm excited to teach "Cryptography: The History and Mathematics of Codes and Ciphers" again this fall. It's my favorite course to teach, and I hope you find it interesting, too.

Here's a copy of the Fall 2015 Syllabus.  Please read this before class on Friday, when we'll talk about various aspects of the course and I'll take your questions on the syllabus.

I thought I would share a couple of links related to Edward Snowden and the NSA. During class, I shared this graphic from ProPublica summarizing the various NSA programs that we've learned about from Snowden's link. I also recommend listening to this interview with one of the reporters who put together the chart, which aired on ProPublica's podcast.

I'll also remind you that you should read the first chapter in our textbook, The Code Book by Simon Singh, before class on Monday. We'll talk about other upcoming assignments during class on Friday.

Practical Cryptography - Resources

As I mentioned in class, you'll want to use reputable and scholarly resources for your final paper. I've listed several categories of resources below, along with examples of each.

For more scholarly sources, check Google Scholar or the Vanderbilt Library's Database Search. For the latter, I recommend selecting a subject (e.g. Business) and leaving the search field blank. For most subjects, you'll receive a list of key databases for that subject. Open the database to search by keyword for articles relevant to your paper.

The Debate: Security vs. Privacy

During class last week, we held a debate on the following proposition:

The US government should be given wide latitude to use electronic surveillance in the interests of national security, even if that means citizens' privacy is not always respected.

We've discussed this proposition several times during the course, notably on the first day of class, when we discussed Edward Snowden's revelations about the NSA, and then a few weeks ago, during our class sessions on Cory Doctorow's novel Little Brother. Last week, we read Simon Singh's treatment of the issue in his book, The Code Book, and so it was time for a proper debate.

Before class, students were asked to make arguments for or against the statement in blog posts. You can read all of those blog posts here.

During class, six students volunteered to debate. Three were randomly assigned to the "PRO" side (security), three to the "CON" side (privacy). Each side had ten minutes to prepare opening arguments, then five minutes each to present opening arguments. Then the jury, consisting of three other students, evaluated the strength of the arguments made and gave each team of debaters feedback. That lead into round two, during which each side responded to the arguments made by the other side during the first round.

How did the debate play out? See this Google Doc capturing the main points of the debate, with notes taken by two of our three notetakers. The third notetaker live-tweeted the debate using the course Twitter account, @practicalcrypto. Below, you'll find a collection of those tweets, which were more entertaining than expected.

As I said at the end of the debate, if we had a bit more class time, we could have brainstormed some compromise solutions that responded to concerns of both sides. We might still come back to that, depending on how the last few weeks of the class go.



Little Brother Debate Map

Here's a capture of the Little Brother debate map we constructed in class on Monday.

Little Brother Debate Map 2014

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Telegraph Security

Telegraph Security

Telegraph SecurityHere's the telegraph security diagram I shared in class today. To better understand it, consider the following scenarios.

Scenario 1a - Messages Sent via Horses, Agent C Decrypts Messages

In this scenario, once Agent C intercepts the ciphertext as it travels via messenger between Agents A and B, he'll decrypt it, then get on his own horse and travel to Agent B's location to cause trouble. (There is no Agent D in this scenario.)  How much time does Agent B have to act on the message before Agent C shows up? Assuming Agent C and the messenger are riding horses with equal speeds, Agent B has precisely as much time as it takes Agent C to decrypt the message.

Scenario 1b - Messages Sent via Telegraph, Agent C Decrypts Messages

Now, after Agent C intercepts and decrypts the message, he sends it along via telegraph to Agent E, who then causes trouble with Agent B. How much time does Agent B have to act on the message before Agent E shows up? Again, precisely as much time as it takes Agent C to decrypt the message. Switching from horses to telegraphs doesn't make Agents A and B any more vulnerable.

Scenario 2a - Messages Sent via Horses, Agent D Decrypts Messages

Now suppose that Agent C merely intercepts the message and gets to Agent D. Agent D decrypts it, then travels via horse to Agent E, who causes trouble for Agent B. How much time does Agent B have to act before Agent E shows up? That would be the time it takes to decrypt the message and the travel time between Agents C and D and Agents D and E. Assuming Agent D isn't located along the A-B route, this means that Agent B has more time than in Scenarios 1a or 1b.

Scenario 2b - Messages Sent via Telegraph, Agent D Decrypts Messages

Same thing, but with telegraphs. Now there's no travel time involved, so Agent B is back to having only the time it takes to decrypt the message as his lead time.

What's the takeaway here? If you're Agent A, then the advent of the telegraph means your buddy Agent B has less time to act on your messages, assuming the other side has to get their intercepted messages to Agent D for decryption. If there's no Agent D, then it doesn't matter if you're sending messages via horses or telegraph, but if there is an Agent D, then you'll want stronger encryption than you used to have.


Academic Integrity Resources

Victory!Some links relevant to our discussion of academic integrity and plagiarism:

Image: "Victory!", Jannis Andrija Schnitzer, Flickr (CC-BY-SA)

Excel Files for Frequency Analysis

Here are the Excel files you'll need for today's in-class activity:

Go ahead and download them, but please don't open them until I ask you to do so.

Friday, August 29th - Resources

Thanks for catching the error in the first problem set. Here's the corrected version: Problem Set 1 (Word) and Problem Set 1 (PDF).

Also, here are copies of the two Excel files I used in class today: Modular Arithmetic and Decimation Cipher.

Finally, I meant to share during class something that I bookmarked this morning, a story on the hacking of Keurig's new scheme for preventing competitors from making coffee pods that work in Keurig coffee machines. I'll call this an example of cryptanalysis, since Keurig's scheme essentially involved encrypted messages between coffee pod and coffee maker. Keurig's competitors have now broken that encryption and are able to send messages of their own -- not unlike how Sir Francis Walsingham sent fake messages to Mary Queen of Scots and her conspirators.

Substitution Ciphers - Some Sources

I hope you found today's cryptanalysis activity interesting. As I mentioned in class, you'll get the chance to work on a new ciphertext from start to finish in your first problem set, which I'll post next week.

Here's the worksheet from today's class with all four ciphertexts. The plaintext for the first one (the shift cipher) comes from this news article on Chelsea Clinton's wedding a few years ago. We'll talk about poem codes in a future class.

The plaintext for the second one (the atbash cipher) comes from WIRED writer Mat Honan's story about how his entire digital life was hacked. I'll say a few words about this on Monday, but if you have the time to read the entire article, do so. It's pretty incredible.

Remember, for Monday you should read the first chapter in Singh and create your blog account. Look for those account creation emails soon. And go ahead and finish decrypting the second ciphertext on the worksheet, too.



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