StarkWare said researcher Avihu Levy has tested an experimental quantum-resistant Bitcoin transaction on the mainnet. Reports indicate that the transaction spent a 10,000-satoshi output in block 964,199 without requiring any changes to Bitcoin’s consensus rules.
The company called it the first transaction of its type. MARA Pool mined the block after receiving the transaction directly through its Slipstream service because its nonstandard format prevented regular Bitcoin nodes from broadcasting it through the public mempool.
StarkWare spokesperson Nathan Jeffay said the transaction required roughly $150 to $200 worth of computational resources. The company added that the process took several hours, demonstrating that individual Bitcoin outputs can be given additional protection under the existing rules, although the approach currently carries significant computational and operational costs.
How StarkWare’s Quantum-Resistant Bitcoin Transaction Works
Levy’s Quantum-Safe Bitcoin (QSB) system, first proposed in April, combines hash-based one-time signatures with computational searches that tie spending authorization to a specific transaction. The design aims to prevent fraudulent spending even if a sufficiently advanced quantum computer eventually breaks the elliptic-curve cryptography used by Bitcoin.
Google researchers estimated in March that a powerful enough quantum computer could theoretically recover a Bitcoin private key within nine to 12 minutes after its public key becomes exposed. According to Google, such a capability could potentially allow an attacker to replace a pending transaction during Bitcoin’s confirmation period.
Levy’s original April proposal estimated that producing a transaction could require between $75 and $150 in GPU computing costs. StarkWare’s completed demonstration placed the actual computational expense at approximately $150 to $200.
QSB is designed to secure individual Bitcoin transactions rather than replace the network’s cryptographic infrastructure. The system allows coins to be transferred into specially protected outputs without modifying the Bitcoin protocol. However, it cannot protect coins whose public keys were already exposed before migration, giving a potential attacker time to analyze those keys before the funds are moved.
The transaction’s nonstandard status under Bitcoin Core’s default relay rules presents a practical limitation. Standard nodes will not propagate the transaction before confirmation, meaning it must be sent directly to a cooperating miner through infrastructure such as MARA’s Slipstream. The approach therefore depends on prebuilt transactions and access to participating miners.
StarkWare CEO Eli Ben-Sasson said QSB could serve as an interim layer of protection while developers work on broader protocol-level defenses. The demonstration offers a way to introduce quantum-resistant spending within Bitcoin’s existing rules instead of replacing the network’s underlying cryptography.
Bitcoin developers are also examining proposals such as BIP-360. The proposed soft fork would introduce a Pay-to-Merkle-Root output type while eliminating Taproot’s quantum-vulnerable key-path spending. Unlike QSB, such an upgrade would require coordination across the Bitcoin network and formal activation.
QSB takes a different approach by operating without waiting for a protocol upgrade. The mainnet demonstration shows that Bitcoin’s existing consensus rules can support a form of quantum-resistant spending, while broader network-wide protections remain under development.
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