Quantum Exposure

How it happens

Most chains authorize spending with elliptic-curve signatures, and Shor's algorithm on a large fault-tolerant quantum computer would recover a private key from its public key. Hashing is affected far less, since Grover's algorithm roughly halves effective search security and can be answered by longer outputs, so mining and address hashing are the smaller part of the problem. The exposure is concentrated where a public key is already visible on-chain: pay-to-public-key outputs, reused addresses, and any transaction sitting in the mempool between broadcast and confirmation. Published resource estimates for the required machine remain far above demonstrated hardware and vary widely between research groups, so the practical near-term issue is migration planning rather than surprise, and NIST completed its first post-quantum signature and key-encapsulation standards in 2024.

What you can actually observe

On-chain data shows how much supply sits at addresses whose public keys are already exposed through reuse or early output types, which is the directly measurable part of this exposure. Check whether the protocol has an upgrade path that allows new signature schemes without moving every coin, such as address versioning or account abstraction, and whether any core research or roadmap document addresses migration. Treat vendor claims of quantum readiness as a document to read rather than a fact, and check which specific scheme is proposed.

What makes it more or less material

Relevant conditions include the share of supply at key-exposed addresses, whether signature schemes can be changed without a hard fork, how long typical funds sit dormant, and whether the design already supports hash-based or lattice-based alternatives.