• StarkWare CPO introduced QSB, a system that aims to enable quantum-resistant Bitcoin transactions without requiring changes to the network protocol.
• QSB uses GPU-powered computation to secure transactions via a new PoW model known as the hash-to-signature puzzle.
• While effective, QSB comes with higher computational costs and complexities.

StarkWare Chief Product Officer Avihu Levy on Thursday introduced a method for executing quantum-resistant Bitcoin (BTC) transactions without requiring any changes to the network's core protocol.

The proposal, Quantum-Safe Bitcoin (QSB), addresses growing concerns about the potential impact of quantum computing on Bitcoin. 

Bitcoin's current transaction system relies on elliptic curve cryptography, which could be broken by future quantum computers using Shor's algorithm. If that happens, attackers could forge signatures and compromise the Bitcoin network.

QSB aims to address the issue by removing reliance on vulnerable cryptographic assumptions while keeping compatibility with Bitcoin's existing infrastructure.

QSB to address security risks in Bitcoin transactions, introduces new PoW mechanism

The system is centered on a new proof-of-work mechanism, a hash-to-signature puzzle. Instead of relying on elliptic curve properties, the system requires users to find a hash output that matches the structure of a valid digital signature. This process is computationally intensive and depends solely on the preimage resistance of hash functions such as RIPEMD-160.

The spending process comprises three main stages, all of which are supported by GPU computing. First, the transaction is fixed via a step called pinning. This is followed by two rounds of digest computation using one-time signature methods, before the final transaction is assembled.

According to Avihu Levy, optimized GPU code can handle tens to hundreds of millions of attempts per second, depending on the hardware. To generate a quantum-safe transaction currently costs between $75 and $150 in cloud GPU usage, with one test completing in about six hours using eight GPUs.

The system's security relies entirely on the strength of the hash functions. It offers up to 118 bits of protection under normal conditions and remains resilient even with quantum speedups, making attacks based on Shor's algorithm ineffective.

These transactions are valid under Bitcoin's current rules but are considered non-standard. As a result, they may need to be sent directly to miners or through specialized services. Each output can also only be spent once.

The work builds on earlier research, including Robin Linus's Binohash and prior discussions around Lamport signatures. The published repository includes ready-to-use scripts and GPU tools, allowing developers to test and reproduce the process today.

The introduction of QSB follows concerns over the fast pace of quantum computing development and its potential to undermine Bitcoin's cryptography.

Meanwhile, BTQ Technologies successfully deployed its Bitcoin Improvement Proposal (BIP) 360 in late March, introducing a quantum-resistant transaction model, Pay-to-Merkle-Root (P2MR). The proposal, live on the company's testnet, aims to solve long-standing vulnerabilities in Taproot.

Bitcoin is trading near $72,300, up 2% over the past 24 hours as of writing.