Blockstream researchers drafted a Bitcoin Improvement Proposal for SHRINCS, a Bitcoin-oriented post-quantum signature design meant to resist quantum attacks without collapsing on-chain capacity. Bitcoin today relies on elliptic-curve signatures that a powerful quantum computer running Shor’s algorithm could theoretically break by deriving private keys from exposed public keys—a risk that already covers large dormant balances, including more than 1.1 million bitcoin tied to Satoshi Nakamoto. NIST-standardized alternatives are far larger than 64-byte Schnorr signatures; Blockstream estimates throughput could fall from about 6.5 TPS with Schnorr to roughly 0.36 TPS with SLH-DSA, while SHRINCS configurations target about 3 TPS. Newer figures describe SHRINCS signatures starting near 324 bytes and reaching about 580 bytes in a 3 TPS setup, growing by roughly 16 bytes per use, with SegWit’s witness discount limiting the block-space cost; earlier proposal material cited a higher minimum size and flagged unaudited status, missing security proofs, and state-management risks. Built on SHA-256 assumptions already central to Bitcoin, SHRINCS targets 128 bits of security against conventional computers and 64 bits against quantum computers, though a mathematical proof of that level has not yet been completed.