Fidelity Digital Assets said future quantum computers could derive Bitcoin private keys from exposed public keys, creating a long-term risk for asset security. The report said current Bitcoin transactions rely on elliptic curve digital signatures and Schnorr signatures, which could be broken by a sufficiently powerful quantum computer running Shor’s algorithm. The report examined the post-quantum signature scheme SHRINCS as a potential upgrade path, citing 48-byte public keys, stateful signatures ranging from 548 to 4,619 bytes, and a 5,777-byte stateless backup option if state is lost. Fidelity said quantum-resistant signatures would significantly increase transaction data size, consume more block space, reduce network throughput, and raise fees during congestion. Any upgrade would require new consensus rules, potentially through a soft fork, as well as broad support from wallets, miners, exchanges, and custodians. Fidelity in July also joined eight other institutions in funding a $15 million Bitcoin security initiative that includes post-quantum research.