Encryption

Encryption is a method of hiding a message from people that you don't want to read it. It involves two stages: (1) encryption which takes the plaintext (message) and translates it to ciphertext (hidden, unreadable message) and (2) decryption which takes the ciphertext and translates it back to plaintext so it can be read. 

An example:

plaintext: meet me in the cafe at twelve
ciphertext: krrs kr dl scr htar ts swrjvr
alphabet used: tigerabcdfhjklmnopqsuvwyz  a=t, b=i etc.

At the heart of encryption has always been matters of national security. After World War II, the largest employers of mathematicians in the United States and Britain have been the government cryptography departments. In fact, the earliest recorded uses of cryptography in Greece and Rome, China and the Ottoman Empire all concerned protecting secrets from the enemy. With recent advances in cryptography, this has become even more pronounced.

Topic A. Unsung Heroes of WWII

Many traditional histories of WWII contain only records of battles and generals. However, recent discoveries and declassification of information have meant that increased attention has been given to the code breakers and encoders who kept the allies' messages safe and broke the Japanese and German messages. A huge portion of fighting a war is knowing what the other side is planning while at the same time keeping your own army organized with encrypted messages. Thousands of encrypted messages were passed on each front of WWII on each day of the fighting.

One of the reasons that the allies won the war is that British and Polish broke the German Enigma code, and that the Americans developed an unbreakable code talkers code for use on the Pacific. The Germans had a machine called the Enigma, which they used to encrypt messages. Before the war started, the Polish intelligence (with help from French intelligence) developed a partial crack of the Enigma machine. This method was developed by Hans-Thilo Schmidt. After the war started, (through a move of great stupidity) Schmidt was put to work doing useless work for the war effort. His work was passed onto the British team at Bletchley Park - which contained Alan Turing.

Alan Turing was already be doing research into what things could be computed. A few of his papers are considered classics in the history of computer science and Turing is generally acknowledged as one of the greatest computer scientists to have ever lived. Using his own and Schmidt's research, Turing developed machines called 'bombes' to decrypt messages produced by Enigma. These decryptions won the Battle of the Atlantic and were very important in winning the war against the Germans.

Sadly, after the war was over, Turing and all of the people at Bletchley Park (who had built the first computer) were not allowed to even admit that they had helped the war effort. One code breaker remembers that people insulted him for not fighting on the front during the war and for being useless during the war effort - and he could do nothing to defend himself. Even their own families were unaware of what they had done to help win the war. Most of the people at Bletchley Park died before their work was declassified. Alan Turing, himself, was prosecuted for being a homosexual and was forced to take 'hormones' to cure him. He became very depressed and committed suicide. 

Also, during WWII, the Americans needed to develop a secure code that couldn't be cracked by the Japanese. A man who had been raised on a Navajo reservation, Philip Johnson, suggested that a Native American language be used as a code. Native American languages are radically different from all other language groups  in the world and are often very complex. Navajo was selected because very few foreign anthropologists had studied them. Altogether, 420 Navajo were recruited into the American military. Their efforts won Iwo Jiwa (a key battle in the Pacific) and were instrumental in winning the last half of the war.

The Navajo code is one of the few that weren't broken in the war. The head of Japanese intelligence later admitted that they had broken all of the other American codes, but they had no idea how to break the Navajo code. Like the cryptanalysts at Bletchley Park, the Navajo's role in the war was classified. It took until 1968 for the American government to declassify it.

Questions

(a) Was is really necessary to keep the Navajo and Bletchley Park secret for 20+ years? What benefits were associated with keeping these secrets classified?

(b) What benefits would have releasing the information have had for the Navajo people and for the code breakers at Bletchley park?

(c) Which were more important: the right of the state to classify the encryption secrets or the rights of the individuals to raise their status in society?

Topic B: Pretty Good Privacy and Phil Zimmermann

The RSA encryption scheme uses an asymmetric encryption key. A symmetric key is like the one shown above - encryption and decryption are exact opposites of each other. If you know how to encrypt a message, you know how to decrypt the message. The RSA scheme, on the other hand, makes encryption very easy and decryption very hard; they are radically different processes. (Incidentally, RSA was developed by Rivest, Shamir and Adlemann based on research by Diffie, Hellman and Merkle who developed DES encryption). 

However, completely encrypting a message using the RSA scheme takes a long time. Phil Zimmermann developed a way of encrypting a symmetric key with the RSA scheme and them encrypting the rest of the message with a symmetric key. The recipient of the message would decrypt the key and then use it to decrypt the rest of the message. Zimmermann called this Pretty Good Privacy or PGP for short.

Zimmermann was greatly concerned with the fact that only banks and government organizations had real privacy on the internet. He created a piece of software that would make it easy for an inexperienced user to use PGP to encrypt their messages before sending it on the internet. Because he feared government intervention, he didn't contact the RSA corporation for permission to use their patented scheme and he uploaded his software to a newsgroup on the Internet.

RSA sued Zimmerman for copyright infringement and the American government made Zimmermann the subject of a grand jury investigation. It seems that RSA and PGP are so powerful that the American government can't break it. They do not want it released to the general public because then they won't be able to read everyone's e-mail and messages. There is already evidence that drug dealers, terrorists and arms dealers are using Zimmermann's PGP and email to replace telephone conversations because PGP can't be broken. It is also a problem for foreign intelligence gathering. Foreign government messages are unbreakable if they use RSA. The American government considered Zimmermann an arms dealer.

Zimmermann, on the other hand, has evidence that human rights groups around the world have been able to encrypt their documents and keep them out of the hands of the governments they are working against. He claims to have received the following e-mail via someone in Latvia in 1991, "Phil, I wish you to know: let it never be, but if dictatorship takes over Russia, your PGP is widespread from Baltic to Far East now and will help democratic people if necessary, Thanks." (Singh, 302).

Source: Singh, Simon. The Code Book. New York: Anchor Books, 1999.

Questions

(a) It is illegal to use RSA or PGP in some countries around the world.  Do you think that this is futile? Explain your answer.

(b) Who is right - the civil libertarians or those who wish to protect national security? Once again, this is a question of the rights of the individual versus the rights of the country. Justify your response.

(c) If you were Zimmermann, would you have released PGP on the internet with no clearance from the people who wrote RSA or from the American government? Why?

3. Information to Retain from this Lesson

You should be able to answer the following questions on a test.

1. Name two famous cryptographers. Explain want they did.

2. Explain the significance to the history of encryption of the following terms:

(a) Alan Turing
(b) Enigma
(c) Code talkers
(d) RSA
(e) PGP
(f) Phil Zimmermann
(g) Bletchley Park
(h) Hans-Thilo Schmidt
(i) Symmetric key
(j) Asymmetric key

3. Who is one of the biggest employers of mathematicians? Why?

4. It has been said that WWI was the chemist's war (mustard gas, etc) and that WWII was the physicist's war (A-bomb, planes) but that WWIII will be the mathematicians' war. Do you agree or disagree: why? Are soldiers so irrelevant?