Beginner Exercism • bash

Diffie-Hellman

Challenge Overview

Diffie-Hellman key exchange.

Instructions

Diffie-Hellman key exchange.

Alice and Bob use Diffie-Hellman key exchange to share secrets. They start with prime numbers, pick private keys, generate and share public keys, and then generate a shared secret key.

Step 0

The test program supplies prime numbers p and g.

Step 1

Alice picks a private key, a, greater than 1 and less than p. Bob does the same to pick a private key b.

Step 2

Alice calculates a public key A.

A = gᵃ mod p

Using the same p and g, Bob similarly calculates a public key B from his private key b.

Step 3

Alice and Bob exchange public keys. Alice calculates secret key s.

s = Bᵃ mod p

Bob calculates

s = Aᵇ mod p

The calculations produce the same result! Alice and Bob now share secret s.

Community Solutions

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The following are the top 3 community solutions by stars:

Solution 1 by @IsaacG (⭐ 1) — View on Exercism
Solution 2 by @thriqon (⭐ 0) — View on Exercism
Solution 3 by @busebd12 (⭐ 0) — View on Exercism

Source: Exercism bash/diffie-hellman

💡 View Solution

#!/usr/bin/env bash

privateKey () {
  (( $# == 1 )) || exit 1
  echo $(( $RANDOM % ($1 - 2) + 2 ))
}

publicKey () {
  (( $# == 3 )) || exit 1
  local -i p=$1 g=$2 private=$3