Bitcoin and Quantum Computing

By Neha Narula Published: April 3, 2026

Source: https://nehanarula.org/2026/04/03/bitcoin-and-quantum-computing.html

Bitcoin's cryptographic signatures would be compromised by a cryptographically-relevant quantum computer (CRQC). The existential threat level depends on two factors: the probability a CRQC emerges within a given timeframe, and the likelihood Bitcoin successfully upgrades before then.

Risk Framework

(A) Likelihood of CRQC appearance by a specific date
(B) Likelihood Bitcoin fails to upgrade by that date

Using Google's quantum research as reference: a Google researcher suggested "a 10% chance of a CRQC existing by 2030." With Taproot activation taking nearly four years, Narula estimates perhaps a 50% chance of successful post-quantum soft fork and wallet migration by 2029, yielding a 5% probability Bitcoin breaks due to quantum threats by 2030.

Key Technical Challenges

Which signature scheme? Post-quantum options involve tradeoffs — larger signatures or longer verification times could increase node costs or reduce transaction capacity.
Transaction consensus handling for non-upgraded UTXOs remains philosophically and technically unclear.
Implementation timeline and strategy present coordination challenges in Bitcoin's decentralized ecosystem.
Wallet ecosystem adoption requires convincing exchanges, custodians, and individual users to upgrade and migrate coins — separate from consensus-layer changes.

Investment and User Perspectives

For investors, the quantum threat should factor into Bitcoin's valuation floor. For developers, the technical uncertainty discourages long-term commitment to non-post-quantum cryptography work.

"I think A is high enough to warrant prioritizing designing, implementing, and evaluating post-quantum signature schemes and consensus upgrades in Bitcoin now."

Common Counterarguments Addressed

FUD claims: the underlying threat is technically valid
CRQC may never exist: betting against "smart people figuring things out" is historically unwise
Current factoring limits: quantum progress doesn't follow intuitive scaling patterns
Other systems face similar risks: banking and internet will likely upgrade; Bitcoin's decentralization makes this harder
Google sabotage theories: two independent truths can coexist

Call to Action

No finalized specifications, implementations, or ecosystem coordination exist. Narula advocates for prioritizing this work through institutional support and developer recruitment.