By Dr Anupam Chattopadhyay

Security systems, to a large extent, rely on the invulnerability of their underlying protocols. Such protocols are built using mathematical primitives, known as ciphers. The study of ciphers, generally called cryptography, is an ancient one. There are detailed historical records, most notably in Second World War, of enciphering a text and attempts to decipher it, by cryptanalysts, which dictated the course of human history. Simple substitution ciphers had been used by ancient Greeks. A variant of such cipher, called one-time pad, was proved to be unbreakable in the 1940s, independently by Claude Shannon and Vladimir Kotelnikov. Despite such a promising result, these kinds of ciphers, generally known as private-key cryptographic primitives, had difficulty in implementation, partly due to the issue of sharing a secret key. Unless the key is known to both the sender and receiver of the message, the enciphering and deciphering – both of which works with the same key – will not be feasible. 

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