In Memory of Stephen Pohlig

The foundation of our modern cyber security world was laid-down in the 1970s with the work of Ron Rivest, Adi Shamar, Whitfield Diffie and Martin Hellman. One person who contributed greatly in the creation of the foundation was Stephen Pohlig. Unfortunately he died last year on 14 April 2017, but he left a great legacy.

In 1977, Stephen graduated with a PhD from Stanford University, and then became part of Martin Hellman’s amazing team at MIT. One of the labs core contributions was the Diffie-Hellman key exchange method. Stephen also contributed greatly to the foundation of cryptography with the creation of the Pohlig-Hellman exponential cipher, and also the Pohlig-Hellman method in solving discrete logarithms.

The exponential cipher cleared the ground for the RSA method. Here is an example:

https://asecuritysite.com/principles_pub/exp

Exponential ciphers uses a form of C=Mᵉ(mod p) to encrypt and decrypt a message (M) using a key of e and a prime number p. The following are some examples:

• message = 5, e=5, p = 53. Try. This should give 5⁵ (mod 53) = 3125 (mod 53) = 51
• message = 4, e=11, p = 79. Try. This should give 4¹¹ (mod 79) = 4194304 (mod 79) = 36

First we create a prime number, such as:

p = 5

The cipher is:

Cipher = Message^e mod p