Bitcoin has completed an experimental quantum-safe transaction using a construction developed by StarkWare, underscoring ongoing efforts to address the security risks that increasingly powerful quantum computers could pose to blockchain networks. The transaction was designed to demonstrate that Bitcoin can adopt a quantum-resistant transaction mechanism without any changes to the network's underlying protocol.

StarkWare confirmed the experimental transaction and credited Avihu Mordechai Levy with developing the Quantum Safe Bitcoin (QSB) transaction scheme. According to the information provided, the work was carried out in collaboration with the MARA Foundation and Tomer Giladi.

The QSB scheme is designed to deliver quantum-resistant security for Bitcoin while leaving the Bitcoin protocol itself unmodified and remaining compatible with the network's existing legacy script constraints.

Scheme targets quantum computing risk

Quantum computing presents a potential long-term challenge for blockchain networks because algorithms such as Shor's algorithm could undermine cryptographic systems that depend on mathematical problems considered difficult for conventional computers. Bitcoin's existing cryptographic architecture could therefore face security concerns if sufficiently capable quantum machines become available. Bitcoin's transaction signatures — both the long-standing ECDSA scheme and the Schnorr signatures introduced with Taproot — rely on elliptic curve cryptography, the family of constructions Shor's algorithm is designed to break. Outputs whose public keys are already exposed, such as early pay-to-public-key transactions and reused addresses, are frequently cited as the most directly at risk, since an attacker would not first need to recover a public key from its hash.

Levy presented the QSB transaction scheme on April 9, 2026, as an approach intended to address that potential threat. The construction is designed to remain secure even under the assumptions associated with Shor's algorithm while avoiding any requirement to change Bitcoin's core protocol.

The development reflects a broader concern across blockchain networks about preparing for advances in computing technology before quantum systems become capable of attacking widely used cryptographic mechanisms. The concern extends beyond blockchain: the U.S. National Institute of Standards and Technology finalized its first post-quantum cryptography standards in August 2024, and migration planning has become a cross-industry exercise. Some blockchain projects, such as the Quantum Resistant Ledger, have employed hash-based signatures since their launch.

StarkWare modifies existing proof-of-work construction

The StarkWare approach builds on a construction referred to as BINOHASH. The development modifies the component considered vulnerable to quantum attacks by replacing a signature-size-based proof-of-work puzzle with a hash-to-signature puzzle.

According to the technical description, the security of the revised mechanism relies on the preimage resistance of RIPEMD-160 rather than the security properties of the replaced component. The change is intended to reduce the scheme's dependence on cryptographic assumptions that could become vulnerable to quantum algorithms. Hash functions are generally considered more resilient to quantum attack than signature schemes, because Grover's algorithm offers only a quadratic speedup against brute-force search rather than the exponential advantage Shor's algorithm provides against factoring and discrete logarithms.

The resulting construction is reported to provide approximately 118-bit second-preimage resistance under a Shor-based threat model. Under Grover's algorithm, the estimated security level is roughly half that figure. These estimates describe the computational difficulty of successfully compromising the construction under different quantum attack scenarios.

Designed to work within Bitcoin's existing limits

A significant feature of the proposal is its compatibility with Bitcoin's existing scripting limitations. The scheme reportedly fits within the legacy Bitcoin script framework, using no more than 201 opcodes and remaining within a 10,000-byte size constraint.

That compatibility could matter because protocol-level changes to Bitcoin generally require extensive technical review and broad ecosystem coordination. A mechanism that can operate within existing script restrictions could offer an alternative route for experimenting with quantum-resistant functionality without immediately requiring a network-wide protocol upgrade.

StarkWare announced the milestone on X:

Quantum-safe Bitcoin, mined on mainnet, Today. Designed by @avihu28 – the first ever quantum-safe Bitcoin transaction was built in collaboration with @MARAFoundation_ and our own @giladi_tom85141 . Every chain faces the same quantum deadline. Today we took a huge step to move…

— StarkWare (@StarkWareLtd) August 26, 2026

The experimental transaction also demonstrates that the concept can move beyond theoretical research into a working proof of concept. The transaction was described as having been mined on Bitcoin's mainnet, providing a practical demonstration of the proposed mechanism under real network conditions.

Low-cost testing could support further research

The technical description estimates the off-chain GPU cost associated with the scheme at a few hundred dollars. While that figure reflects an experimental implementation rather than a prediction of future production costs, relatively accessible computational requirements could make further testing easier for researchers and developers.

The reported mainnet demonstration provides evidence that quantum-safe transaction concepts can be tested within Bitcoin's existing operational environment rather than remaining solely theoretical proposals.

An experimental step, not a full upgrade

The development does not mean Bitcoin has been fully upgraded to withstand all possible future quantum attacks. It instead represents an experimental step toward evaluating alternative cryptographic mechanisms before quantum computing reaches a level capable of threatening current blockchain security.

As quantum computing research advances, blockchain developers are increasingly examining ways to preserve transaction security against potential future attacks. StarkWare's QSB construction adds another technical approach to that effort, with its focus on protocol compatibility, hash-based security assumptions, and practical implementation.

According to the report, the successful experimental transaction could provide a foundation for additional research into quantum-safe Bitcoin transactions and the broader challenge of preparing decentralized networks for the next generation of computing technology. The open questions for observers include whether the scheme's security estimates hold up under independent cryptanalytic review, and whether further mainnet experiments of this kind shape wider discussion of how established networks should prepare for quantum computing.

Source: CoinTrust