A Bitcoin transaction designed to resist future quantum-computing attacks was mined on the mainnet on August 27, 2026, in a demonstration led by the Starknet Foundation. The transaction was completed without a soft fork, hard fork or upgrade to Bitcoin Core.
Damian Chen, vice president of growth at the Starknet Foundation, presented the transaction at Bitcoin Asia in Hong Kong. He described it as the first post-quantum-resistant Bitcoin transaction confirmed on the mainnet.
How the transaction works
The approach was developed by Avihu Levy, a researcher at StarkWare. It addresses a potential vulnerability during the period when a Bitcoin transaction is visible in the mempool but has not yet been confirmed.
In a future scenario involving sufficiently capable quantum computers, an attacker could potentially use exposed cryptographic information to forge a signature and redirect funds before confirmation. The demonstrated method, known as quantum-safe Bitcoin or QSB, avoids relying on a conventional signature alone.
Instead, the process generates millions of candidate signatures until it finds one with a specific structural characteristic intended to prevent disclosure of the vulnerable information during the confirmation window. The process is deliberately computationally intensive, with a single transaction taking hours to produce.
Chen said the added authorization mechanism is designed to prevent an attacker from creating a valid fraudulent transfer even if the attacker obtains a wallet’s public key and derives its private key using a sufficiently powerful quantum computer.
Transaction required direct miner submission
The transaction did not use Bitcoin’s standard transaction format. As a result, ordinary Bitcoin nodes could not process it through the public mempool. It was instead sent directly to a miner willing to include it in a block.
MARA’s Slipstream service mined the transaction. The demonstration therefore showed that the technique can be used on Bitcoin’s existing mainnet without a network-wide software change, while also highlighting that broader deployment would require support from the network’s infrastructure.
Quantum computing remains an emerging threat rather than an immediate capability. Researchers have warned that future machines could challenge cryptographic systems used by Bitcoin, although current quantum computers have only performed relatively limited computations. Bitcoin developers and industry participants continue to debate when preparations should become a network-wide priority.
“The question to me has never been when will quantum arrive,” Chen said. “We know quantum will arrive at some point, but the question has always been, how long will it take you to be ready when quantum does arrive?”
