Quantum-Resistant Bitcoin Transaction Confirmed on Mainnet

First Quantum-Resistant Bitcoin Transaction Confirmed on Mainnet Without Protocol Change

Bitcoin saw its first known quantum-resistant transaction on its mainnet today, processed through MARA’s private Slipstream mempool. The transaction utilized a method dubbed “Quantum Safe Bitcoin,” developed by StarkWare’s Avihu Levy.

This innovation addresses a critical vulnerability in how Bitcoin secures funds during transit, notably without requiring any changes to the network’s consensus rules. However, even its creators acknowledge it as a temporary measure rather than a definitive solution.

Bitcoin held in hashed addresses, specifically the P2PKH format commonly used by most wallets, is generally considered secure against quantum attacks. The vulnerability emerges when these funds are spent.

The act of sending Bitcoin necessitates the revelation of the wallet’s public key. This key remains exposed in the mempool for approximately ten minutes, the typical confirmation window, presenting an opportune moment for a quantum computer to exploit.

Levy’s Quantum Safe Bitcoin aims to close this vulnerability window without altering consensus rules. The system modifies Binohash, a technique pioneered by BitVM creator Robin Linus. It achieves this by encasing each transaction within a proof-of-work puzzle. The security of this puzzle relies on hash functions believed to be resistant to quantum attacks, rather than on the digital signature itself.

Levy first detailed this approach in a paper published in April. He estimated its security at approximately 118 bits against Shor’s algorithm and roughly half that against Grover’s algorithm, with an estimated additional cost of a few hundred dollars in GPU processing time.

The method fits within Bitcoin’s existing script limits, thus avoiding the need for a soft fork. However, it does require a non-standard transaction format, which only private mempools like Slipstream are currently equipped to accept. Isabel Foxen Duke, head of the MARA Foundation, characterized the mining of this transaction as a stopgap, not an endorsement of private mempools as a long-term solution.

“We do not believe private mempools are an appropriate long-term solution for Bitcoin quantum resistance,” Foxen Duke stated. She added that MARA is prepared to continue supporting Slipstream for emergency situations while the network works towards a consensus-level change.

Levy credited StarkWare’s Tom Giladi for completing the implementation, building upon earlier work by Linus and Ethan Heilman. He was careful to describe the outcome as “a research quirk and not the straightforward way for Bitcoin to become” quantum-ready.

The urgency surrounding this issue stems from a Google paper released earlier this year. The paper indicated that a sufficiently powerful quantum computer could compromise the private keys of Ethereum’s 1,000 wealthiest wallets in less than nine days, as previously reported.

Researchers at Project Eleven have also highlighted the same mempool-stage vulnerability that Quantum Safe Bitcoin targets, warning that funds could be intercepted from a transaction before it is finalized. Bitcoin developers are also pursuing their own solutions, including a proposal known as BIP-361. This proposal would involve phasing out old, quantum-vulnerable addresses, beginning with new deposits and eventually blocking withdrawals.

Blockstream has adopted a different strategy, implementing post-quantum signatures on its Liquid sidechain since April. This allows users to opt into protection without having to wait for Bitcoin’s native upgrade path.