Bitcoin processed its first quantum-resistant transaction on mainnet August 26 in block 964,199, moving 10,000 satoshis using hash-based cryptography, according to StarkWare researchers. The transaction employed Avihu Levy's QSB method via MARA Pool's Slipstream service.
The demonstration uses a stopgap approach rather than a protocol-wide fix. StarkWare framed the transaction as a proof of concept for quantum-safe custody on Bitcoin's existing layer without requiring consensus changes to the network's cryptographic foundation. Bitcoin currently secures transactions through ECDSA, an elliptic curve algorithm considered vulnerable to attack by sufficiently powerful quantum computers.
Quantum computing poses a theoretical but acknowledged threat to current public-key cryptography. A large-scale quantum computer could potentially derive private keys from their corresponding public keys, allowing an attacker to forge signatures and spend unspent transaction outputs. The timeline for such capability remains uncertain; estimates from cryptography researchers range from years to decades depending on quantum hardware advances.
Hash-based signatures derive security from cryptographic hash functions rather than discrete logarithm problems. They require larger signature sizes and additional blockchain overhead compared to ECDSA, which explains why Bitcoin has not adopted them protocol-wide. The Slipstream service bundles quantum-safe signatures into Bitcoin transactions using existing opcodes, demonstrating that quantum resistance can be layered onto the network without core changes.
StarkWare's demonstration adds to growing industry focus on post-quantum cryptography. The National Institute of Standards and Technology finalized quantum-resistant algorithms in August 2022 and has continued standardization efforts. Ethereum researchers have explored similar quantum-safe transaction structures on their network.
The transaction required no Bitcoin software upgrade and created no precedent for mandatory protocol adoption. It operated within Bitcoin's existing rule set, using only available transaction structures and script operations. Multiple institutional actors including exchange operators and custody providers have begun testing quantum-resistant signing schemes ahead of any potential threat materialization.
The experiment took place on Bitcoin mainnet rather than testnet, meaning the transaction is permanent and immutable on the longest chain. This distinguishes it from prior quantum-safety research limited to sandboxed environments. StarkWare says the approach remains a defensive measure and not a replacement for consensus-level protocol changes if quantum threats accelerate.
