A StarkWare researcher has published a paper outlining a way to protect bitcoin (BTC) transactions from quantum-computing attacks without a soft fork, The Block reported on Thursday.

Researcher Avihu Levy (아비후 레비) introduced “Quantum Safe Bitcoin,” or QSB, in a paper released on Wednesday. QSB is a method that gives bitcoin transactions quantum resistance using only existing legacy script constraints.

According to the paper, standard bitcoin transactions currently rely on the Elliptic Curve Digital Signature Algorithm (ECDSA). ECDSA can be broken if a quantum computer with sufficient performance runs Shor’s algorithm.

Levy proposed QSB to address the issue. QSB adopts a Binohash-based structure that uses a one-time signature scheme built into bitcoin script, instead of elliptic-curve cryptography, for transaction security. Binohash secures transaction integrity through a proof-of-work puzzle based on signature size, but that puzzle can also be broken by quantum computing.

QSB provides a “hash-to-signature” puzzle to remove that vulnerability. Under the structure, the spender must solve it using only hash operations rather than elliptic-curve operations. Levy explained that it can be resistant to quantum attacks that target elliptic-curve cryptography.

But the paper shows clear limits in practicality. Levy said QSB costs about $75 to $150 per transaction based on current cloud GPUs. That is far higher than bitcoin’s average transaction fee of 30 cents.