Post-Quantum Encryption Comes to HopToDesk

Most security problems are about right now. Someone tries a password, someone clicks a bad link, and the damage happens today. Encryption has a stranger problem, and it works in the other direction: an attacker who cannot read your traffic today can simply keep it.

The name for this is harvest now, decrypt later. A recorded remote session is a bundle of encrypted bytes that means nothing to whoever captured it. But the key that unlocks those bytes was agreed with a piece of maths that a large enough quantum computer would solve. Nobody has such a machine today. If one is ever built, every recording made before that day becomes readable, and a remote desktop session is a rich thing to read: the screen, the keystrokes, the clipboard, the files that moved across it.

That is why this work happens before the machine exists rather than after. HopToDesk sessions are now protected against it.

What changed

The part of a connection that a future quantum computer threatens is the very beginning: the moment the two ends agree on a secret key. Everything after that point is protected by symmetric encryption with a 256-bit key, which is already considered strong enough for a quantum future.

So that is the part we replaced. The two ends now perform two key agreements instead of one:

• The classical one, X25519, which HopToDesk has always used.
• A post-quantum one, ML-KEM-768, the key exchange standardized by the United States National Institute of Standards and Technology in 2024.

Both results are mixed together into the single session key. This is called a hybrid handshake, and the word hybrid is doing real work. An attacker has to break both to get anything. Old maths and new maths protect the same session, so a future quantum computer is not enough on its own, and a flaw discovered in the newer algorithm cannot make a HopToDesk connection weaker than it was before this change.

The exchange is also bound to the connection it belongs to. The pieces of the post-quantum handshake are folded into the key along with the secret itself, so a tampered or swapped value does not quietly downgrade the session. It fails immediately instead.

What you have to do

Nothing.

There is no setting, no checkbox, and no key to manage. When two current HopToDesk clients connect, the hybrid handshake is used automatically. Connect to a machine that is still on an older version and the session still works normally, using the previous encryption, so nothing breaks while a fleet updates at its own pace.

There is also no cost to notice. The post-quantum values ride inside messages the two ends already exchange, so the handshake gains no extra round trip, and the extra data is about a kilobyte. Nobody watching their screen will see a difference.

This covers the desktop apps and the browser client. The identity signature that proves a host is the machine you think it is stays on its current algorithm, deliberately: forging a signature is a live attack that has to happen during the connection, and it cannot be performed later against a recording. The recording problem is the one that needed solving now.

Why we think this is worth doing today

It is fair to ask whether this is early. Cryptographically useful quantum computers do not exist, and predictions about when they might arrive vary by decades.

The answer is that the deadline for this particular problem is not the day such a machine is switched on. It is today, because the data being protected is being captured today. Any session that matters in five or ten years needs to be protected with tomorrow's cryptography now, not when the news breaks. Governments and standards bodies have been saying exactly this for years, which is why the algorithm exists and is standardized at all.

For most people using HopToDesk this is invisible, and that is the point. Security that needs a decision from every user is security that half of them get wrong.

Get it

Update to the current version and it is already there. Download HopToDesk at www.hoptodesk.com/download, and manage your machines from the HopToDesk Dashboard.