## Cryptography

#### The History and Mathematics of Codes and Code Breaking

Here's Erin's paper on the Playfair cipher [PDF].

Previous

Next

1. #### Courtney

Erin-

I really enjoyed the initial backstory of the relationship between Wheatstone and Playfair. The explanation that followed was very clear and easy to understand, especially with the addition of the various diagrams at the end. After reading this paper, I feel confident that I could successfully encrypt and decrypt a message using the Playfair Cipher, and I can also see how it would be impossible to do so if the recipient lacked the keyword. Great job - this paper was compelling and well-written.

Courtney

3. #### Rob Rice

I found the historical section of your paper to be the most interesting part. I think your paper explains the origin of the Playfair in an informative and entertaining way. Specifically, your description of Playfair and Wheatstone is funny and detailed. This historical background provides a context for the reader to appreciate the development of the Playfair cipher. You also provide notable, concrete examples such as the use of this cipher in the agony columns and by John F. Kennedy. This works well to highlight the practical value of the cipher.

The most clearly explained aspect of your topic was how to encipher a message using the Playfair. Your step-by-step walk through of a sample message is easy to follow, and the accompanying diagrams greatly elucidate the process. After reading your paper, I felt confident that I could use it correctly to send a secret message. Overall, it is easy for the reader to gain an understanding of how the Playfair works.

I would like to know more about the cipher's use in war. You mention that the Playfair was used in the Boer War, World War I, and World War II. Perhaps little information is available about this topic, but I would be interested to learn some more details if they exist. For example, was use of the Playfair limited to specially trained soldiers, or was it a widely used technique? What is the story behind the deciphering of the Playfair--what approach was used to successfully crack it? Are there any specific military victories that can be attributed to the Playfair? A few such details would really round out the paper.

You make some excellent connections to other topics in the course. For example, you contrast the Playfair to the well-known cipher machines Enigma and SIGABA, noting the different situations in which each would be used. You also connect your topic to the Vigenére and elaborate on the popularity of substitution ciphers during this time period. Finally, you also give an account of the lasting impact of the Playfair on the world of cryptography, including the attempt to build upon the digraphic nature of the Playfair to create a trigraphic cipher, and the eventual application of algebra to cryptography. On the whole, I enjoyed reading your paper and feel that you've done an excellent job writing about this unique cipher.

4. #### John Zeleznak

Your essay was very well-rounded and progressed nicely through the history, as well as the mathematics, of the code. I really liked how you compared the Playfair cipher to other ciphers we have studied in orded to show how it contrasted from techniques that preceeded it. You did a very thorough job of explaining the historical background of the cipher and how it was implemented in various military action. However, I personally would have liked some statistics that showed the difficulty of the cipher just to give it some perspective. Overall, I feel like there could have been a little more emphasis on the math of the Playfair cipher, especially how to go about decrypting it. It was a little vague. Also, I think including your visual aides within the text would help your explanation tremendously. My favorite part of your essay was learning about how it was used in specific instances by John F. Kennedy and the British military. It formed a better connection with the audience and really gave the cipher a historical perspective.