Photo by Markus Winkler on Unsplash
When we talk about cybersecurity, most of us are thinking about viruses, hacking, maybe password leaks. But there’s another looming threat creeping quietly through the background: quantum computers.
Yep, those ultra-powerful, not-yet-widely-available machines that could, one day, crack the encryption we trust to keep our digital lives private. That includes everything from our money to our messages.
And it’s not science fiction — it’s more like a ticking clock.
That’s why what the engineers behind Signal just pulled off is getting serious applause in the cryptography world. They managed to upgrade the world’s most famous end-to-end encryption protocol to stand up to future quantum attacks — and they did it without breaking how the app works today.
Let me walk you through what happened, why it matters, and what makes it such a technical marvel.
Why does quantum computing even matter here?
All modern encryption relies on something engineers call “one-way functions.” These are math problems that are easy to do one way, but nearly impossible to reverse — unless you’re a quantum computer.
Today’s devices can’t solve them in any reasonable amount of time. But someday, quantum machines will. And when that day comes, algorithms like RSA and elliptic curve cryptography (used all over the internet, including in Signal’s old system) become pretty much useless.
In other words, someone could capture encrypted traffic now, store it, and just wait for a powerful enough quantum computer to come along and unlock it later.
Scary? Yes. Urgent? That’s the tricky part.
For decades, experts have been saying we’re 15–30 years away from this so-called “cryptopocalypse.” But they’ve been saying that, well, for 30 years.
So most of the tech world has chosen to kick the can down the road. Quantum-safe encryption is expensive, technically difficult, and plays second fiddle to more immediate threats like ransomware.
Signal didn’t wait.
Signal’s leap: From two ratchets to three
If you’ve never dug into how Signal protects your messages, here’s the quick version:
- Signal uses something called the Double Ratchet algorithm. With every message you send or receive, it updates the key — kind of like throwing away your lock and making a new one each time.
- This gives you two key benefits: forward secrecy (old messages stay secret even if one key is compromised) and post-compromise security (you can recover secure communications even if someone briefly listens in).
It’s extremely clever. But its foundation — elliptic curve cryptography — is vulnerable to quantum attacks.
In 2023, Signal took a first step by upgrading the initial handshake with a quantum-safe mechanism called PQXDH. But the rest of the ratchet still used quantum-vulnerable keys.
Now, they’ve added a third ratchet.
Meet SPQR: The Sparse Post-Quantum Ratchet
The new third ratchet is called SPQR. It’s built using a powerful but bandwidth-hungry algorithm called ML-KEM-768 — basically, a chunk of math that quantum computers can’t easily break.
Great news, right?
Well, not so fast.
The encryption key involved here is about 2,272 bytes. That’s roughly 71 times bigger than the slim 32-byte keys Signal used before. Sending one of those with every message? On unreliable networks? In asynchronous conversations where one person might be offline for hours?
It’s like trying to sneak an elephant through a door built for cats.
But Signal’s engineers, working with researchers from PQShield, AIST, and NYU, found a workaround: erasure coding.
Solving the elephant problem
Here’s how the magic works:
- They break the massive 2,272-byte key into smaller pieces.
- Then they use erasure codes, a clever trick that allows the full key to be rebuilt with only a subset of those pieces.
- That way, even if a few packets go missing (as can happen on shaky networks), the receiver can still recover the key.
It’s kind of like sending puzzle pieces, knowing the other person only needs most of them to recreate the full picture.
Plus, they split up the computations so the process is fast enough to avoid dragging your connection down.
The final twist? Signal kept the old ratchet system running in parallel. Every time you send a message, your app pulls keys from both the trusty double ratchet and the new quantum-safe one. It blends them together using a cryptographic function — protecting you with both systems at once.
If one of them ever fails — whether due to quantum computing or something else — the other still protects your messages.
As Charlie Jacomme, a security researcher at INRIA, put it: “It nicely combines the best of both worlds.”
So… does this change anything for me?
Photo by Claudio Schwarz on Unsplash
Not really. And that’s the best part.
You won’t see a different UI. You won’t notice longer loading times or bigger chat bubbles. Your messages will just quietly become a whole lot harder for any future eavesdropper to read.
If you use Signal or another app built on the Signal Protocol, your messages are becoming quantum-resistant — without you lifting a finger.
The update is rolling out over time. Until then, the system falls back to the already highly secure double ratchet. Once it’s live, you simply keep messaging like always.
Why this is a big deal
What Signal managed to do — add full quantum protection without disrupting usability or exposing new vulnerabilities — is a rare kind of engineering challenge. It requires deep knowledge not just of math and cryptography, but of real-world software design, user behavior, and the messy realities of internet connectivity.
Brian LaMacchia, a former Microsoft cryptography lead, called it “a solid, thoughtful improvement.”
And Matt Green of Johns Hopkins summed it up with a metaphor I love:
“If the normal encrypted messages we use are cats, then post-quantum ciphertexts are elephants. So the problem here is to sneak an elephant through a tunnel designed for cats.”
Signal just snuck the elephant through.
And we’re all a little safer because they did.
Why it matters, even if you don’t worry about quantum computers
You might not care about quantum tech right now. But think of SPQR like putting your seatbelt on before the crash happens. It’s insurance for the future — and a smart way to make sure the messages you send now don’t become someone else’s reading material 20 years from today.
Even better: For once, you don’t need to understand any of this to benefit from it.
You just keep texting. Signal takes care of the rest.
🗝️ Keywords: quantum encryption, Signal post-quantum security, SPQR Signal, Signal Protocol upgrade, ML-KEM, end-to-end encryption, secure messaging, cryptography, quantum-safe ratchet.
