StarkWare, the blockchain infrastructure company behind Ethereum layer-2 network Starknet, announced that the first quantum-safe Bitcoin transaction has been mined on the Bitcoin mainnet. The transaction tests a method to protect funds from future quantum attacks without requiring changes to the network's consensus rules.
The transaction used Quantum-Safe Bitcoin (QSB), a method developed by StarkWare researcher Avihu Levy, who published the research in April. StarkWare engineer Tomer Giladi later implemented the proposal as a working mainnet transaction.
Bitcoin currently uses elliptic-curve cryptography to secure transactions. A sufficiently powerful quantum computer running Shor's algorithm could theoretically break this encryption to derive private keys and steal funds. Protecting the network could eventually require either a hard fork—which introduces incompatible rules and can split the network—or a soft fork, which can introduce new rules while remaining compatible with older nodes.
StarkWare CEO Eli Ben-Sasson said the company still favors a soft fork as the long-term solution, while QSB provides a way to protect individual holdings before a network upgrade occurs. "What today's successful transaction offers Bitcoin is a reassurance that holdings can be protected before that happens," Ben-Sasson said.
In June, Coinbase's quantum advisory council estimated that roughly 7 million Bitcoin could be vulnerable due to exposed public keys and address reuse.
QSB adds a second, quantum-resistant lock based on hash functions rather than elliptic curves. It uses "signature grinding," which performs computational work off-chain to find a transaction hash that Bitcoin will accept as a validly formatted signature.
StarkWare acknowledged that QSB does not make Bitcoin fully quantum-safe but protects specific transactions using hash-based security. The method cannot protect addresses with already-exposed public keys and currently requires transactions to be sent directly to miners.
"This amazing feat should not be viewed as a message saying 'Bitcoin is prepared for the quantum threat,'" Ben-Sasson wrote, emphasizing the need for serious soft forks to address the broader quantum threat to Bitcoin.
