Fidelity: Bitcoin Keys Could Be Vulnerable to Quantum Attacks

Fidelity warned that advances in quantum computing could one day allow attackers to recover Bitcoin private keys from public data recorded on the blockchain. The firm highlighted a “store now, crack later” threat in which data collected today could be decrypted when quantum technology improves.

The risk centers on the cryptographic methods Bitcoin uses to prove ownership. Bitcoin relies on the elliptic-curve digital signature algorithm and the secp256k1 curve. When an address is spent from, the transaction reveals the public key linked to the private key.

A sufficiently powerful quantum computer running Shor’s algorithm could, in theory, derive a private key from that public key and then move funds. Quantum hardware capable of carrying out that attack has not been built, and timelines for such machines remain uncertain.

The advisory targets custodians, exchanges and long-term holders that keep large Bitcoin balances. The notice points out that reused addresses, hot wallets and systems that repeatedly publish public keys increase exposure because they provide the public inputs an attacker would need. Encrypted backups and archived key material could be recorded now and attacked later when quantum capabilities improve.

Fidelity recommended avoiding address reuse, moving funds to fresh addresses periodically, maintaining private keys offline when possible and preparing migration plans to signature schemes designed to resist quantum attacks once standards and wallet support are available. The firm encouraged custodians to monitor developments in post-quantum cryptography and to evaluate multi-signature configurations that combine different key types as interim protection.

Standards work is under way. The U.S. National Institute of Standards and Technology is running a post-quantum cryptography process to select new public-key algorithms. Implementing post-quantum signatures in Bitcoin would require protocol changes and widespread software upgrades across wallets, exchanges and node operators.

Most cryptographers view large-scale quantum computers capable of breaking elliptic-curve signatures at Bitcoin key sizes as uncertain and not expected in the immediate future, though estimates vary. Fidelity framed the advisory as a risk-management notice because the blockchain permanently records public inputs that could be targeted later.

The advisory does not claim an imminent attack. It joins other notices from digital-asset managers urging practices that reduce exposure while cryptographic standards and practical implementations are finalized.