SHRINCS Post-Quantum Signatures for BTC

In Bitcoin news today, a group of cryptography researchers has published a draft specification for SHRINCS, a post-quantum signature scheme for Bitcoin transaction authorization.

The draft, authored by conduition, Ethan Heilman, Mikhail Kudinov, Oleksandr Kurbatov, Jonas Nick, and a contributor known as remix7531, describes a hash-based design that combines a compact stateful signing path with a stateless fallback.

Bitcoin’s Quantum Defense Takes a Major Step Forward

Adam Back’s Blockstream has published a Bitcoin Improvement Proposal for its experimental SHRINCS signature scheme.

The proposal targets a major future threat from sufficiently powerful quantum computers.

SHRINCS has already… pic.twitter.com/xGIowGaQzX

— BSCN (@BSCNews) August 27, 2026

Signature size is particularly important for Bitcoin because signatures consume scarce block space. SHRINCS is designed to reduce that burden by giving each public key two signing paths, trading added implementation complexity for a more compact primary signing option.

This crypto quantum computing news dropped as BTC USD is mostly flat on the day, down a modest -0.3% and currently trading for $78,700, with daily trading volume sitting at $27.2Bn.

Bitcoin News Today: Two Signing Paths, One Public Key

The scheme combines a compact stateful component, called FXMSS, with a larger stateless fallback based on a customized variant of SLH-DSA. The stateful path produces signatures ranging from 548 to 4,619 bytes, depending on the selected tree structure and signing history.

The stateless fallback, intended for cases in which the signing state is unavailable, lost, corrupted, or reset, has a fixed signature size of 5,777 bytes. The combined public key is 48 bytes.

Blockstream Research, which proposed the design, has described an earlier configuration in its materials as starting near 324 bytes and increasing by roughly 16 bytes per additional signature.

Its parameter search evaluated 25,935 candidate stateless configurations. The selected parameter set minimizes signature size among candidates that meet the targeted security level and signature budget while keeping key generation, average signing, and worst-case verification costs below those of SLH-DSA-SHA2-128s.

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Why Hash-Based Cryptography Is the Conservative Bet

JUST IN: The first post-quantum resistant Bitcoin transaction was mined today.

“It required no soft forks. It required no hard forks. It required no core protocol upgrades. And it’s live today.” pic.twitter.com/YyZbHhm8HI

— Bitcoin Magazine (@BitcoinMagazine) August 27, 2026

SHRINCS relies on the security of its underlying SHA-256 hash function, which is already fundamental to Bitcoin’s security. The specification targets NIST security category 1, corresponding to 128 bits of classical security and 64 bits of quantum security.

The draft contrasts that approach with post-quantum schemes from other families that also rely on hash-function security but require additional hardness assumptions, including lattice problems. Its authors argue that conservative assumptions have particular value for Bitcoin because outputs may remain unspent for long periods.

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A Draft for Further Research

In other Bitcoin news today, SHRINCS remains a draft specification. It sets out key-generation, signing, and verification algorithms, but its formal security proof is still listed as incomplete in the document.

The proposal reflects work aimed at preparing for a potential quantum-computing threat to elliptic-curve signatures. Blockstream Research notes that a sufficiently capable quantum computer could recover a private key from an exposed public key and spend the funds it protects.

It also says that nobody knows when, or whether, such a machine might exist, while migrating Bitcoin to new cryptography would take years. That uncertainty is why work on post-quantum options is taking place before the threat materializes.

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