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Bitcoin’s quantum-security work took two visible steps on August 26. StarkWare published a mined Bitcoin transaction using its Quantum-Safe Bitcoin method, or QSB. A team including Blockstream researcher Jonas Nick also released a detailed SHRINCS specification.
A sufficiently capable quantum computer using Shor’s algorithm could derive a Bitcoin private key from its public key and forge a signature. Publicly known machines remain far below that level. Can Bitcoin protect exposed public keys before quantum hardware becomes capable enough to exploit them?
QSB creates an extra hash-based lock without changing Bitcoin’s consensus rules. The sender first performs an intensive offchain search for parameters that satisfy a Bitcoin Script condition. Those parameters then form the added lock.
StarkWare sent the transaction through MARA’s Slipstream service because public nodes generally decline to relay this script format. Slipstream sends eligible transactions directly to a miner. Bitcoin’s consensus rules accepted the transaction once miners included it.
The method also carries a high computing cost. The project repository estimates $75 to $150 in cloud GPU costs for its documented setup. StarkWare said the latest run cost several hundred dollars.
Timing creates another limitation. The public key must remain hidden until the coins reach the extra lock. Pay-to-public-key-hash and native SegWit addresses usually reveal that key when users spend them.
Taproot outputs and older pay-to-public-key outputs expose the public key earlier. QSB therefore does not cover an address whose public key became public before the protective transaction.
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SHRINCS, short for Shrunken SPHINCS, targets Bitcoin’s block-space limits and hardware-wallet constraints. Its specification currently reads “BIP: ?,” “Status: Draft,” and “Assigned: ?.”
The proposal uses a 48-byte public key. Stateful signatures range from 548 to 4,619 bytes, depending on the signing path. A stateless recovery signature reaches 5,777 bytes. By comparison, Taproot uses a 64-byte Schnorr signature. An earlier SHRINCS implementation ran on Liquid in March. Liquid operates as a Bitcoin sidechain with its own network rules.
Bitcoin nodes currently lack SHRINCS verification code. The specification also says its security proof remains unfinished. Independent cryptographic review must address that gap before the proposal can advance.
Each compact SHRINCS signature uses a fresh one-time signing slot. Wallets must record every used slot. Restoring an old backup could reuse a slot and expose enough information for signature forgery.
The broader quantum-security discussion now includes three separate pieces. QSB offers a specialized transaction method under current rules. SHRINCS provides a candidate signature scheme for protocol review.
BIP-361 proposes a process for moving funds away from quantum-vulnerable signatures. Its timetable depends on an approved post-quantum signature standard and output type. SHRINCS could supply one candidate for the signature component.
Developers would still need to define the output type, implement the code, review it, and secure network support. Only then could the proposed BIP-361 migration clock begin.
QSB sits outside that timetable because it uses a specialized path available today. Wider use would still require software that wallets, exchanges, and custodians can support consistently.
StarkWare has identified one mined QSB transaction. Reproducing it requires project-specific tools, significant computation, and miner-direct access. The project has not yet published a standard-wallet workflow for creating and spending the protected output.
Bitcoin’s August 26 quantum-security work covered both immediate and longer-term paths. QSB showed a hash-based protection method under current consensus rules, while SHRINCS offered a draft signature design. BIP-361 remains dependent on an approved signature standard, output type, implementation, review, and network support.
