Nic Carter says quantum computing is the biggest long-term risk to bitcoin’s core cryptography and urges developers to treat it with urgency, not science fiction.
In an essay published Monday, Coin Metrics’ co-founder explains in plain language how bitcoin’s keys work and why quantum matters. Carter writes that users start with a secret number (a private key) and derive a public key using elliptic curve math on the secp256k1 curve, the basis of ECDSA and Schnorr signatures.
He describes this transformation as consciously one way: easy to calculate forward, impossible to reverse under classical assumptions. “Bitcoin’s entire cryptographic premise is ‘there exists a one-way function that is easy to compute in one direction and impossible to reverse,'” he writes.
To build intuition, Carter compares the system to a giant number scrambler. Going from private to public is effective for honest users, he says, because they can use a shortcut known as “double and add” to reach a result quickly. He adds that there is no comparable shortcut in the opposite direction.
For non-specialists, he offers a deck-shuffle analogy: you can repeat the same sequence of shuffles to reach an identical final order, but an observer cannot look at the shuffled deck and deduce how many shuffles were used.
Carter argues that the concern is that a sufficiently powerful quantum computer could erode that asymmetry by making progress on the discrete logarithm problem that underpins bitcoin’s signatures. In his telling, routine network behavior also increases exposure: when coins are spent, a public key is exposed on the chain.
He says it’s secure today because it’s not practical to convert a revealed public key back to the private key, but quantum advances could change that calculation, especially if addresses are reused and multiple keys remain visible for longer.
He does not call for panic. Carter says the point is to plan.
In the short term, he emphasizes basic hygiene such as avoiding address reuse so that public keys are not exposed any longer than necessary. In the longer term, he urges society to prioritize post-quantum signature schemes and realistic migration paths, framing them as engineering rather than a far-fetched thought experiment.
The essay is the first in a short series; Carter said on X that parts II and III will arrive in the next few weeks and will cover “post-quantum break scenarios.”
