Bitcoin has recorded its first known quantum-resistant transaction on the mainnet. The transaction was mined through MARA’s private Slipstream mempool using a method known as Quantum Safe Bitcoin, developed by Avihu Levy of StarkWare.
While hashed addresses, such as the P2PKH format utilized by most wallets, are generally considered secure against quantum attacks, vulnerabilities emerge when funds are spent. The act of sending Bitcoin requires revealing the wallet's public key, which remains exposed in the mempool during the roughly ten-minute confirmation window—a period that could potentially be exploited by a quantum computer.
To address this gap without altering consensus rules, Levy's scheme modifies Binohash, a technique created by BitVM contributor Robin Linus. The method wraps transactions in a proof-of-work puzzle relying on hash functions resistant to quantum attacks. According to Levy's April paper, the approach offers an estimated security of around 118 bits under Shor’s algorithm, with an added cost in GPU time.
Because the design fits within Bitcoin's current script limit, it avoids the need for a soft fork. However, it requires a non-standard transaction format that is currently accepted only by private mempools like MARA's Slipstream. Isabel Foxen Duke, head of the MARA Foundation, emphasized that the method serves as a stopgap rather than a long-term endorsement of private mempools, noting that MARA supports Slipstream for emergency cases while the network pursues consensus-level solutions.
Industry urgency has grown following a Google research paper indicating that powerful quantum computers could compromise Ethereum's top wallets, alongside warnings from Project Eleven regarding mempool-stage vulnerabilities. Bitcoin developers are actively exploring other solutions, including the BIP-361 proposal to phase out quantum-vulnerable addresses, while Blockstream has introduced post-quantum signatures on its Liquid sidechain.
