Beginner Exercism • javascript

Diffie Hellman

Challenge Overview

Diffie-Hellman key exchange.

Source: Exercism javascript/diffie-hellman

💡 View Solution

export class DiffieHellman {
  constructor(p, g) {
    if (!this.isPrime(p) || !this.isPrime(g)) {
      throw new Error('Arguments must be prime');
    }
    this.p = p;
    this.g = g;
  }

  isPrime(n) {
    if (n <= 1) return false;
    for (let i = 2; i <= Math.sqrt(n); i++) {
      if (n % i === 0) return false;
    }
    return true;
  }

  getPublicKey(privateKey) {
    if (privateKey <= 1 || privateKey >= this.p) {
      throw new Error('Invalid private key');
    }
    return BigInt(this.g) ** BigInt(privateKey) % BigInt(this.p);
  }

  getSecret(theirPublicKey, myPrivateKey) {
    return BigInt(theirPublicKey) ** BigInt(myPrivateKey) % BigInt(this.p);
  }
}