Suppose that two parties A and B wish to setup a common secret key (D-H key) between themselves using the Diffie-Hellman key exchange technique. They agree on 7 as the modulus and 3 as the primitive root. Party A chooses 2 and party B chooses 5 as their respective secrets. Their D-H key is (

A) 3

(B) 4

© 5

(D) 6

# Diffie-Hellman key exchange,a interesting Gate question,help!

**shreya**#1

The Diffie–Hellman key exchange method allows two parties that have no prior knowledge of each other **to jointly establish** a shared secret key over an insecure channel.

This key can then be used to encrypt subsequent communications using a **symmetric key cipher.**

The simplest and the original implementation of the protocol uses **the multiplicative group of integers modulo p, where p is prime, and g is a primitive root modulo p.**

3^2 mod 2.

2^5 mod 7 = 4.

The D-H key is g^(ab) mod p.

I recommend see wikipedia,very good and exhaustive explanation: