A newly published scheme is proposing a method to secure Bitcoin transactions against quantum computing risks, claiming it achieves protection without major changes to the network’s existing protocols. This approach, known as Quantum Safe Bitcoin (QSB), was introduced in a research paper by Avihu Levy, a developer at StarkWare, a company specialized in cryptographic solutions for blockchain systems such as zero-knowledge proofs and scalability technologies.
How QSB aims to address quantum threats
The main concern addressed by the proposal is the vulnerability of Bitcoin’s current transaction model to quantum attacks. Bitcoin traditionally relies on elliptic curve digital signatures (ECDSA) based on the secp256k1 curve. With advances in quantum computing, the cryptography underlying this system could become susceptible to algorithms capable of rapidly solving the discrete logarithm problem.
QSB suggests moving away from full dependence on elliptic curve security by leveraging hash-based techniques. More specifically, the proposal retains ECDSA as a check but shifts the foundational security to the difficulty of finding hash pre-images, a computational problem resistant to known quantum algorithms.
This approach takes inspiration from previous proposals, such as Binohash, which embed hash-based signature schemes in Bitcoin’s scripting language. QSB modifies this idea to remain compatible with the network’s operational constraints, ensuring new transactions can be constructed without breaking existing consensus rules.
Central to QSB is a “hash-to-signature” mechanism. A transaction’s public key is hashed using RIPEMD-160, and the output is evaluated to produce a valid ECDSA signature. Only a small fraction of outputs will fit the stringent criteria for valid signatures, resulting in a computational challenge comparable to a proof-of-work problem.
Operational impact and limitations
The new scheme claims to eliminate the risk posed by Shor’s algorithm, which threatens elliptic curve security, by relying instead on the properties of cryptographic hash functions. Even with quantum advancements, only a quadratic speed increase would be possible through Grover’s algorithm, leaving what the proposal describes as sufficient safety margins for practical purposes.
A key advantage of the QSB approach involves compatibility with existing Bitcoin scripting constraints, such as restrictions on opcode usage and script size. No protocol upgrades or so-called soft forks would be needed, a detail likely to appeal to developers who favor stability in the network’s foundational rules.
However, QSB transactions have significant limitations. They exceed standard relay policy limits, meaning they would not automatically propagate across the Bitcoin network as ordinary transactions do. Instead, these transactions would require miners to be contacted directly, for example, using specialized services that bypass default relay filters.
The computational cost of generating these transactions is another drawback. Estimates suggest generating a valid transaction could require between $75 and $150 in cloud computing resources, with successful attempts taking hours on multi-GPU machines. These figures reflect the computational intensity of searching for suitable hash-to-signature outputs.
So far, the scheme remains at a prototype stage. While the research paper and code for generating scripts are available, full demonstration of on-chain transaction assembly and successful broadcast has not yet been presented by Levy or collaborators.
StarkWare, the company behind QSB’s author Avihu Levy, is recognized for its work in blockchain cryptography, particularly in pioneering scalable and privacy-preserving solutions for Ethereum and other blockchains through zero-knowledge technology. The new proposal contributes to a broader effort in the crypto community to future-proof digital assets against quantum computational threats.
Avihu Levy highlighted that this design aims to enhance quantum resilience for Bitcoin without necessitating contentious upgrades, aiming to stimulate further research in the field of hash-based cryptography on established blockchain systems.
