Rich by Coin

A new proposal outlines a way to create quantum-resistant Bitcoin transactions without changing the network protocol. The design replaces elliptic-curve assumptions with hash-based puzzles and Lamport signatures. The approach shifts computational work to transaction creators and is presented as a temporary workaround rather than a permanent fix. Bitcoin transactions could be made resistant to future quantum attacks without changing the network’s core protocol, according to a proposal from StarkWare researcher Avihu Mordechai Levy.

We present QSB, a Quantum Safe Bitcoin transaction scheme that requires no changes to the Bitcoin protocol and remains secure even in the presence of Shor’s algorithm, Levy wrote. The proposal replaces elliptic-curve signatures with hash-based cryptography and Lamport signatures, an early signature scheme considered resistant to quantum attacks. Since Lamport signatures are post-quantum secure, and they sign a cryptographically strong identifier of the transaction, it is not possible to modify the transaction without producing a new Lamport signature—which the attacker cannot forge, even with quantum computing capabilities, Levy wrote. At the center of the design is a cryptographic puzzle that must be solved before a transaction is broadcast.

The paper estimates that finding a valid solution would require about 70 trillion attempts. Unlike Bitcoin mining, the computation happens before the transaction reaches the network. Users perform the work off-chain and submit a transaction that already includes proof that the puzzle was solved. Levy estimates the puzzle could be solved using commodity hardware such as GPUs at a cost of a few hundred dollars per transaction.

The scheme is designed to operate within Bitcoin’s scripting limits of 201 opcodes and 10,000 bytes. The paper notes these limits are extremely restrictive because every opcode counts toward the total, even if it appears in an unused script branch. To fit within those limits, the system combines Lamport signatures with hash-based puzzles in a layered transaction structure. It also introduces “transaction pinning,” which requires anyone attempting to modify the transaction to solve the puzzle again.