- a16z says no cryptographically relevant quantum computer exists yet, making near-term blockchain breakage unlikely this decade.
- Post-quantum encryption needs earlier adoption, but digital signatures and blockchains face far lower immediate quantum risk.
- Implementation bugs and side-channel attacks pose greater near-term threats to blockchains than quantum computing advances.
Fears that quantum computers will soon break blockchain cryptography continue to grow, however new analysis urges restraint. According to a16z, claims about imminent quantum threats overstate current capabilities and risk costly, premature security changes. The firm released its assessment this month, focusing on blockchains, encryption, and digital signatures.
Quantum Timelines and Technical Reality
According to a16z, a cryptographically relevant quantum computer does not exist today and remains unlikely this decade. Such a system would require fault-tolerant machines capable of running Shor’s algorithm against RSA-2048 or secp256k1.
Current platforms lack sufficient qubits, gate fidelity, and sustained error-corrected depth. Notably, some companies cite “quantum advantage” demonstrations, however these focus on narrow, impractical tasks.
Others reference thousands of qubits, which often describe quantum annealers, not gate-model systems. a16z also highlighted confusion around “logical qubits,” noting true cryptographic attacks would require thousands of fully error-corrected logical qubits.
Scott Aaronson recently acknowledged faster hardware progress, yet later clarified that small-scale Shor demonstrations do not threaten real cryptography. Factoring trivial numbers, such as 15, does not equate to breaking blockchain security.
Encryption Risks Differ From Signatures
a16z stressed that harvest-now-decrypt-later attacks already threaten encrypted data requiring long-term secrecy. As a result, post-quantum encryption demands earlier adoption despite performance costs.
Chrome, Cloudflare, Apple iMessage, and Signal have deployed hybrid encryption combining classical and post-quantum methods. However, digital signatures face different risks. Signatures do not hide data, so past signatures cannot be retroactively forged.
Therefore, a16z said immediate migration to post-quantum signatures remains unnecessary. Zero-knowledge proofs, including zkSNARKs, also avoid harvest-now risks because they reveal no confidential information.
Blockchains Face Uneven Exposure
Most blockchains, including Bitcoin and Ethereum, rely on signatures rather than encryption, limiting harvest-now exposure. Privacy-focused chains differ because encrypted transaction data could be later exposed.
a16z cited Monero and Zcash as examples where design choices affect quantum risk severity. Bitcoin faces separate challenges unrelated to quantum timelines.
Governance speed, abandoned coins, and exposed public keys complicate migration. Meanwhile, a16z emphasized that implementation bugs and side-channel attacks pose far greater near-term risks than quantum computers.
