Quantum‑resistant signing

Blockstream Research posted and demonstrated an opt‑in way to use quantum‑resistant signatures on the Liquid Network, broadcasting live transactions that used the new verifier on March 3, 2026. (blog.blockstream.com) Instead of changing Liquid’s rules, Blockstream built the verifier as a Simplicity smart contract that users can choose to lock their assets into; funds moved into those contracts require the new, post‑quantum signatures to spend. (blog.blockstream.com) The verifier implements a scheme called SHRINCS, which is a hash‑based signature design — meaning its security rests on one‑way hash functions rather than number‑theory problems that quantum computers exploit — and it offers a “stateful” normal mode with very small signatures plus a larger “stateless” fallback for recovery scenarios; Blockstream reports the optimized stateful signatures are on the order of a few hundred bytes. (eprint.iacr.org ) (registry.projecteleven.com) Blockstream published an implementation and supporting research (including a GitHub repository for SHRINCS) and said it broadcast two demonstration transactions on Liquid mainnet to prove the flow works in production. (github.com/BlockstreamResearch/shrincs-cpp) (blog.blockstream.com) Separately, Blockstream researcher Jonas Nick proposed SHRIMPS on March 30, 2026, a follow‑on hash‑based design intended to allow multiple devices (separate hardware or wallets) initialized from the same seed to sign independently while keeping signatures around ~2.5 kilobytes, addressing the practical problem of multi‑device backups. (delvingbitcoin.org) (atlas21.com) Blockstream cautioned that this deployment does not make Liquid entirely immune to quantum attacks — critical pieces such as the Bitcoin peg mechanism, Confidential Assets commitments, and Liquid’s block‑signing/federation protocol still use classical signatures today — so the protection applies only to assets explicitly moved into the new Simplicity contracts. (blog.blockstream.com)