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StarkWare says the first quantum-safe Bitcoin transaction has been mined on mainnet using a hash-based spending construction that works without changing Bitcoin’s consensus rules.
The August 26 transaction used Quantum-Safe Bitcoin, or QSB, developed by StarkWare researcher Avihu Levy. MARA mined the nonstandard transaction after it was submitted directly through its Slipstream service. The transaction is publicly recorded on Bitcoin.
QSB Shifts Bitcoin Security From Elliptic Curves to Hash-Based Protection
Normal Bitcoin transactions rely on ECDSA or Schnorr signatures whose elliptic-curve security could be broken by a sufficiently capable quantum computer running Shor’s algorithm.
QSB instead uses a hash-based construction whose security depends on preimage resistance. Levy’s implementation retains ECDSA as part of Bitcoin’s existing verification machinery, but the scheme does not depend on elliptic-curve hardness for its security.
The method uses signature grinding. Offchain computation searches for transaction parameters that produce a hash matching Bitcoin’s required signature encoding. The construction fits within Bitcoin’s existing legacy Script limits of 201 non-push opcodes and 10,000 bytes.
StarkWare said the current process costs several hundred dollars in computation, making QSB impractical for routine payments. Engineer Tomer Giladi helped turn Levy’s April research into the mainnet implementation.
MARA Mines Nonstandard QSB Transaction Through Slipstream
QSB transactions are valid under Bitcoin consensus rules but exceed default relay-policy limits, meaning ordinary nodes will not propagate them through the standard public mempool.
The August 26 transaction therefore used MARA Slipstream, which provides a direct path for consensus-valid nonstandard transactions to reach a miner.
That remains a practical limitation. Broader use would require other miners or submission services to accept QSB transactions directly, or changes that make the format compatible with standard relay policy.
Mainnet Transaction Does Not Make Bitcoin Quantum-Safe
The transaction demonstrates that individual Bitcoin outputs can use a quantum-resistant spending construction under today’s consensus rules. It does not make the Bitcoin network as a whole quantum-safe.
QSB also cannot protect coins whose public keys were already exposed before migration, because a future quantum attacker could derive the private key before the protective transaction reached a miner.
StarkWare continues to support a protocol-level upgrade as the longer-term solution. For now, QSB provides a working mainnet path with high computation costs and direct miner submission as its main practical constraints.
