Fidelity Warns Quantum Computers Threaten Bitcoin Private Keys

Fidelity Digital Assets has warned that Bitcoin's private key protections may eventually require replacement due to future quantum computer threats. The warning comes from a recent analysis published by Fidelity, which states that cryptographically relevant quantum computers do not currently exist but could potentially undermine the mathematical assumptions securing transaction authorization and place funds at risk.

The private keys used in Bitcoin allow owners to authorize transactions without relying on an intermediary. Wallets use these private keys to produce digital signatures that prove control without disclosing the secret key. The current standard for Bitcoin transactions uses either Elliptic Curve Digital Signature Algorithm (ECDSA) or Schnorr signatures, which rely on the difficulty of solving the elliptic curve discrete logarithm problem with classical computers.

However, a sufficiently powerful quantum computer running Shor's algorithm could solve this problem and derive private keys from corresponding public keys. Researchers are evaluating quantum-resistant signature systems that rely on hash functions rather than elliptic-curve cryptography. One such system is SHRINCS, which combines efficiency with a recovery path.

SHRINCS' current design specifies a 48-byte public key, stateful signatures ranging from 548 to 4,619 bytes, and a 5,777-byte stateless signature. A future quantum-resistant Bitcoin upgrade could accommodate different security requirements, but implementing such a system would require new consensus rules and support from wallet providers, miners, node operators, exchanges, and custodians.