Venture capital giant Andreessen Horowitz (a16z) has released a detailed analysis asserting that near-term quantum threats to blockchain cryptography are overstated. The firm concludes that a cryptographically relevant quantum computer, capable of breaking the encryption underpinning major blockchains like Bitcoin and Ethereum, does not exist today and is unlikely to materialize within this decade.
The report clarifies that such a machine would require thousands of fully error-corrected logical qubits to run Shor’s algorithm against standards like RSA-2048 or the secp256k1 curve used in Bitcoin. Current quantum hardware lacks the necessary qubit count, gate fidelity, and error correction. a16z noted that many public claims of "quantum advantage" refer to narrow, impractical tasks or quantum annealers, not the gate-model systems needed for cryptographic attacks.
Encryption vs. Signature Risks: a16z distinguishes between different cryptographic threats. Harvest-now-decrypt-later attacks are a legitimate concern for encrypted data requiring long-term secrecy, prompting early adoption of post-quantum encryption by companies like Chrome, Cloudflare, and Signal. However, for digital signatures—the backbone of most blockchain transactions—the risk profile is different. Since signatures do not hide data, past signatures cannot be retroactively forged, making an immediate migration to post-quantum signatures less urgent.
Blockchain-Specific Exposure: The analysis finds most blockchains, including Bitcoin and Ethereum, face limited immediate quantum risk as they primarily use signatures. Privacy-focused chains like Monero (XMR) and Zcash (ZEC) have greater exposure due to their use of encryption. a16z emphasized that implementation bugs and side-channel attacks currently pose far greater near-term threats to blockchain security than quantum advances.
Concurrently, the industry is actively preparing for the long-term threat. Coinbase has established an independent advisory board dedicated to quantum computing and blockchain security, featuring experts like Stanford's Dan Boneh, quantum theorist Scott Aaronson, Ethereum Foundation researcher Justin Drake, and EigenLayer founder Sreeram Kannan. The board will publish research and guidance for the ecosystem.
This preparation highlights a shift from theory to engineering. Data shows quantum-related discussions on Bitcoin developer mailing lists rose to over 10% in 2025. The Ethereum Foundation has also declared post-quantum security a top priority, forming a dedicated team and running post-quantum devnets.
Amid these technical preparations, MicroStrategy executive Michael Saylor issued a warning, stating that the "greatest risk to Bitcoin is ambitious opportunists advocating protocol changes." This comment underscores the tension between preparing for future threats and maintaining the protocol's stability, as seen in debates around proposals like BIP-110.
