Post-Quantum Encryption Isn’t Quantum Encryption
PSA! “Post-quantum encryption” isn’t the same thing as “quantum encryption.” I realized recently that many people are confused about this, which is understandable.
Here’s the misconception that people have: They think that because we’ve almost achieved cryptographically relevant quantum computing, then that means that when someone says they’re working on “post-quantum cryptography,” then that means they’re working on updating classical encryption over to quantum encryption.
But that’s not quite right. Let’s break it down.
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First of all, “Q-Day” is defined as the future tipping point when a quantum computer becomes powerful enough to break standard public-key encryption algorithms (such as RSA and elliptic-curve cryptography). That’s also why I referred above to “cryptographically relevant” quantum computing. We do already have quantum computers right now, technically speaking, but they aren’t that functional yet.
Next, whenever we talk about this concept of a quantum computer breaking encryption, we’re specifically referring to two algorithms for quantum computers that have already been developed. These are Shor’s and Grover’s algorithms.
Not all classical encryption is considered vulnerable to Shor’s and Grover’s algorithms. Symmetric encryption is considered safe. Asymmetric encryption is considered vulnerable because it relies on the difficulty of factoring very large prime numbers. If quantum computers can do anything, they are going to be very good at factoring large primes.
Now, coming back to the misconception: People assume that in order to fix encryption’s vulnerability to quantum computers, we’re in the process of replacing classical encryption with quantum encryption. But that’s not right. We’re in the process of replacing old classical encryption that’s known to be vulnerable to being broken by quantum computers, with updated classical encryption standards that are thought to be more resilient to attack by quantum computer.
Quantum key distribution, (a subset of actual quantum cryptography) does exist, but when people refer to the “post-quantum cryptographic migration mandate,” that’s not what they’re referring to. They’re just referring to updating classical encryption so that it’s still classical, but in a way that’s considered less vulnerable to this new looming danger.
