StarkWare researcher proposes ‘quantum-safe’ Bitcoin transactions without a soft fork

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A StarkWare researcher has published a new paper outlining a measure to protect Bitcoin (BTC) transactions from quantum computing without a soft fork.

In the paper published Thursday, researcher Avihu Levy introduced Quantum Safe Bitcoin (QSB) as a scheme that enables Bitcoin transactions to be quantum-resistant using only existing legacy script constraints.

According to the paper, standard Bitcoin transactions are reliant on ECDSA (Elliptic Curve Digital Signature Algorithm) signatures that could be broken by sufficiently powerful quantum computers running Shor’s algorithm.

To solve this problem, the researcher proposed QSB, which replaces reliance on elliptic curve cryptography in transaction security with a construction based on Binohash that uses a one-time signature scheme embedded in Bitcoin Script.

Binohash achieves transaction integrity through a proof-of-work puzzle based on signature sizes. This puzzle, however, can also be broken by quantum computing, the paper said.

QSB removes this vulnerability by creating a "hash-to-signature" puzzle that requires the spender to solve a puzzle based on pure hashing rather than elliptic curve math, making it resistant to quantum attacks that break elliptic curve cryptography.

"Since this puzzle depends only on the pre-image resistance of RIPEMD-160 (not on any elliptic curve assumption), it is fully resistant to Shor's algorithm," the researcher explained.

Is it practical?

According to Levy, the cost of QSB is estimated at roughly $75 to $150 per transaction in current cloud GPU compute, which is much higher than the current average bitcoin transaction cost of 30 cents.

As such, Levy said this tool should be used as a "last-resort measure," citing the cost and complex user experience. Still, the researcher called this a "practical cost" as the required computing process can be done in parallel and can be scaled across multiple GPUs.

While the scheme can operate under current Bitcoin rules, it remains experimental and impractical for widespread use, facing constraints from opcode and script size limits and not yet supporting all use cases, such as Lightning Network channels.

"To the extent that the quantum threat is believed to be real, it remains necessary to continue the ongoing effort to research and implement the best possible solution for Bitcoin — one that is maximally efficient, user-friendly, and answers Bitcoin's needs, through protocol-level changes," the paper said.

As quantum threats to Bitcoin advance faster than initially expected, Google researchers recently warned, QSB offers an approach that avoids protocol changes. In contrast, other solutions, such as BIP-360, a proposed soft fork that introduces a whole new output type for Bitcoin, require broad consensus.

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