CISSP 7.1 - Asymmetric Cryptography (Part 2 of 2)

This episode of the ISC2 Certified Information Systems Security Professional (CISSP) exam prep series continues Domain 3’s tour of asymmetric systems, moving past RSA to the other public key algorithms every candidate needs to know. It widens the map to the alternatives that trade size, speed, and power differently — and looks ahead to the technology that could reshape the entire field.

Frequently Asked Questions

What is ElGamal, and what is its catch?

ElGamal extends the ideas behind the Diffie-Hellman key exchange into a full public key system that can encrypt and decrypt messages, not just swap keys. One big advantage was that it was placed in the public domain and free to use at a time when its main rival was still patented. Its drawback is that it roughly doubles the size of whatever it encrypts, which becomes a genuine burden when pushing large volumes of encrypted data across a network.

Why does elliptic curve cryptography pack so much strength into a small key?

ECC builds its security on the math of points on a curve: even when you know the starting point and the ending point, recovering the hidden integer multiplier is extraordinarily hard. This is the elliptic curve discrete logarithm problem, and experts believe it is tougher than the factoring problem RSA relies on. The payoff is efficiency — a short elliptic curve key delivers the same protection as a much longer RSA key, which is why it shines in constrained, low-power devices.

How do two strangers agree on a secret without ever sending it?

That is the magic of Diffie-Hellman key exchange. Two parties publicly agree on a couple of large numbers, each picks a private random number and combines it with the shared numbers to produce a value they can safely send, and when each side folds the other’s value into their own private number, both arrive at the same secret — which never travels across the wire. For the exam, remember Diffie-Hellman is a key exchange method, not an encryption algorithm on its own.

How could quantum computing rewrite this entire field?

Quantum computing swaps ordinary one and zero bits for quantum bits, or qubits, that behave in richer ways. If a genuinely powerful quantum computer arrives, it could solve the very factoring and logarithm problems that RSA and Diffie-Hellman depend on, rendering them insecure overnight. The same technology could also power new, tougher algorithms — researchers have already built lab versions of quantum key distribution, though it remains experimental.

What should you do about the quantum threat right now?

Think in terms of shelf life: assume an attacker may quietly copy your encrypted data today and simply wait until future quantum tools can crack it open. If that data will still be sensitive by then, the exposure is already yours to manage. Also remember the first practical break of modern cryptography may never be announced, so plan today for a post-quantum world and weigh how long each secret truly needs to stay protected.

Reference: This article is based on concepts discussed in CISSP 7.1 - Asymmetric Cryptography (Part 2 of 2).