News from Quantum Realm

Post-quantum cryptography is the set of public-key algorithms designed to stay secure against a future quantum computer strong enough to break existing encryption. This collection of algorithms runs on ordinary hardware today, but the point is the underlying math, chosen so that the shortcuts a quantum computer offers won't apply.

‘Harvest now, decrypt later’ is a strategy to gain access to sensitive information with a long delay built in. An adversary records and stores encrypted data today, and waits for a quantum computer that can break the encryption (the so-called ‘Q-Day'). The data might not look worth stealing this year, but it could be valuable the moment Q-Day arrives and makes it readable.

There's no single answer to this question. Every number you'll see belongs to one architecture, and moves when the architecture does.

Bitcoin has carried quantum risk from the time of its first blocks because the earliest coins published their public keys straight on-chain. Ever since, the number of disclosed keys has continued to grow. But the risk isn't a simple running total. How much BTC sits behind an exposed key rises and falls as coins are created, reused, moved, and spent, and it won't wait for a quantum computer to arrive before it becomes a problem.

Q-Day is the day a quantum computer becomes strong enough to break the public-key cryptography that secures almost everything online, from bank logins and encrypted messaging to the signatures on your crypto wallet. It hasn't happened yet, and no publicly known machine still comes close.

If we’re talking about whether crypto is safe today, then the answer is yes. Yet, the answer is a resounding no when it comes to safety by design. Those are two different answers, and everything serious about this question lives in the space between them. No quantum computer can touch your coins at this very moment. The machine that could hasn't been built. What has been built is the certainty that the signatures guarding nearly every chain are breakable in principle, plus a migration race to replace them that most chains are losing. Here's what each layer of "safe" means.

No. A quantum computer can't break a blockchain's ledger or the mining that secures it. The stored history stays right where it is. What a (capable enough) quantum computer one day will be able to break is the signature layer, the cryptography that decides who gets to move funds. That one distinction lurks behind every "quantum kills crypto" headline, and it changes what cryptocurrency holders need to worry about.

Sadly, Bitcoin isn’t quantum safe. The reason comes down to a specific piece of math. ECDSA (and Schnorr, for Taproot) over the secp256k1 curve authorizes every Bitcoin transaction, and Shor's algorithm dismantles both on a sufficiently large quantum computer. That's the short answer. As for the longer, more complicated one, it touches upon which coins are exposed, how migration would work, where the timeline sits, and what holders can do before the protocol catches up.

Quantum computing’s threat to crypto is the risk the market has, for the most part, blissfully ignored. But cryptographers and security researchers keep warning that a large enough fault-tolerant quantum computer will be able to break the encryption protecting almost all wallets on every major blockchain that relies on elliptic-curve signatures.

An Expert Assessment of Post-Quantum Risk Across the Top-10 Layer-1 Blockchains