The plaintext from today’s cryptanalysis exercise comes from this Guardian (UK) story about an MI6 worker found murdered in his apartment. MI6 is the UK version of the CIA, an all-purpose espionage agency. The victim apparently worked at GCHQ, the top-secret crypto unit over in the UK and an offshoot of the crypto unit at Bletchey Park during World War II. had an update to the story yesterday. Police still aren’t saying if they know how or why he was killed, although they’ve stated it wasn’t because of his personal life. The victim, Gareth Williams, worked with colleagues at GCHQ and the National Security Agency (NSA) to analyze coded al Qaeda messages related to a planned bombing of transcontinental flights. Remember our discussion on the first day about not tipping the “bad guys” off that you can read their encrypted messages? Here’s a quote from the Wired story that references that idea:

The NSA shared the e-mails with British prosecutors but wouldn’t allow them to use the evidence in an early trial of the suspects out of fear of tipping off Rauf that he was under surveillance. It was only after Rauf was reportedly killed in a U.S. drone attack that the NSA allowed prosecutors to use the e-mails to convict the other suspects.

Here’s the Excel file I used today to help decipher the ciphertext in today’s exercise. As I mentioned, the substitution cipher used was the atbash cipher in which the cipher alphabet is the plain alphabet in reverse order. Even thought the method used was very simple, the ciphertext still looks suitably cryptic on first glance.  However, as we saw in class today, a simple substitution method can lead to a very quick cryptanalysis.

Also, nice job on the responses to the reading questions for today. I was impressed with your thoughtfulness and the examples you mentioned in support of your arguments. The pre-class reading questions and the free writes you’ll do during class are opportunities for you to practice your writing and communication skills in a low-stakes environment.