World Leaders in Cryptography: Whitfield Diffie

Prof Bill Buchanan OBE
4 min readFeb 21, 2024

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When I finally look back on my career, one of the highlights will certainly be the opportunity to meet one of my cryptography heroes: Whitfield (Whit) Diffie. Overall, he is one of the greatest Computer Scientists ever, and — along with Marty Hellman — was one of the first to propose the usage of public key encryption and co-created the Diffie-Hellman (DH) key exchange method.

Overall, the Diffie-Hellman method is still used in virtually every Web connection on the Internet and has changed from using discrete log methods to elliptic curve methods. In 2015, Whitfield was also awarded the ACM Turing Prize — and which is the Nobel Prize equivalent in Computer Science.

The Father of Cryptography

Whitfield (Whit) was first exposed to cryptography at the age of 10 (5th Grade) when a teacher gave a talk for a day and a half. He got serious into cryptography through the development of DES (Data Encryption Standard), and Whit thought that the standard should have more bits to make it more secure.

In the early 1970s, Larry Roberts — the creator of the Internet — started and investment in the security for ARPANET. This started a major drive into finding methods that could protect the data that travelled over the public network. Larry was a great believer in investing in academic work, and this kick started a drive toward network security — mainly focused on cryptography at the time.

Though his interested in the DES method, Whit took a trip in 1974 to the IBM Yorktown Research Lab, and hoped to meet the creator of the DES method: Horst Feistel. Unfortunately, Horst was not around at the time of the visit, but he was told that Marty Hellman at Stanford would be an interesting person for him to chat with.

Whit then set up a short meeting Marty at Stanford (in fact, just 30 minutes) and where they discovered that they had shared interests. In fact, they got on so well that Marty invited Whit and Marty (his wife) to dinner that evening. And, so, Whit arrived at Stanford, and started to investigate the encryption key distribution problem. In four years, Whit and Marty discovered public key encryption.

Whit was initially motivated at the IFF (Identification, Friend or Foe) radar system [here], and where a plane could challenge another plane to identify itself by re-encrypting an encrypted message. The problem with this is that an enemy plane could simply play back the message and produce a valid encrypted message. The work has further led to the IFF Mark XII method.

For this, he understood that a weaknesses of digital systems would be the opportunity to copy digital signals (as with the IFF system). He thus spotted that you could perhaps recognize the solution to a problem without actually being able to solve it yourself. This could then be applied to negotiate keys with someone that you have never met before. And, so, the discrete log method of exchanging keys was born.

Around 1978, it is thought that a chat David Chaum, motivated him into the creation of cryptocurrency.

A great shinning light in his world was his wife, Mary (Fisher), and who’s charm helped support Whit throughout his career.

The Diffie-Hellman method

The Diffie-Hellman (DH) method is perhaps one of the greatest inventions in Cybersecurity and was created by Whitfield Diffie and Marty Hellman:

With the DH method, Bob creates a random value (b) and Alice also creates a random value (a). Next, Bob computes:

B=g^b (mod p)

and sends it to Alice. Alice computes:

A=g^a (mod p)

and sends this to Bob. Bob raises the value of A to the power of b and takes (modp), and Alice raises B to the power of a and takes (mod p). In the end, they will have the same shared value:

g^{ab} (mod p)

This can then be used to derive an encryption key that they can use for a secure tunnel (Figure 1). Overall, p is the large prime number, and also known as the shared modulus between Bob and Alice.

Figure 1: The Diffie Hellman key exchange method [here]

Conclusions

Whit just inspires me to do great things in cryptography.

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Prof Bill Buchanan OBE

Professor of Cryptography. Serial innovator. Believer in fairness, justice & freedom. Based in Edinburgh. Old World Breaker. New World Creator. Building trust.