SHRINCS BIP published: Quantum-secure Bitcoin comes with a catch

Blockstream researchers have officially published a Bitcoin Improvement Proposal (BIP) introducing SHRINCS, an experimental post-quantum signature scheme designed specifically to safeguard Bitcoin against future quantum computing threats. Advanced quantum computing poses a severe theoretical risk to public-key cryptography, potentially enabling the reverse engineering of private keys from public keys. SHRINCS seeks to provide a practical hash-based defense tailored to Bitcoin's architectural constraints. Unlike standardized NIST-approved post-quantum algorithms that are between 38 and 123 times larger than current ECDSA or Schnorr signatures, SHRINCS minimizes footprint to a base size of 548 bytes. Utilizing Bitcoin's Segregated Witness structure, SHRINCS would allow the network to maintain transaction throughput at around 3 transactions per second (TPS), preventing the severe throughput drops below 0.5 TPS seen with alternative post-quantum schemes. Despite its advantages, the BIP introduces trade-offs, including stateful key tracking on user devices and potential signature bloat upon repeated transactions. Furthermore, while the scheme has operated on Blockstream's Liquid sidechain, formal security proofs and broad community governance consensus remain significant hurdles before activation.