Quantum computing startup Alice & Bob published a preprint on the IACR Cryptology ePrint Archive on Thursday showing that a system with 29,588 physical cat qubits could crack a Bitcoin private key in 61.8 minutes. The theoretical attack targets secp256k1, the elliptic curve algorithm securing Bitcoin signatures, using circuits originally compiled to break RSA-2048 encryption.
Cat Qubits vs. Google's Quantum Model
Alice & Bob utilizes a proprietary superconducting architecture called cat qubits, which suppress bit-flip errors directly in hardware so error-correction routines only need to address phase-flips. This drastically reduces the physical qubit count compared to previous benchmarks. In 2023, the firm estimated that solving a 256-bit elliptic curve logarithm would require 126,133 cat qubits and nine hours.
By contrast, a March 30 whitepaper from Google Quantum AI outlined an architecture needing fewer than 500,000 physical qubits that could break a key in just nine minutes. Because Google’s speed falls within Bitcoin’s 10-minute block time, it could enable "on-spend attacks" intercepting unconfirmed transactions. However, because Alice & Bob’s process takes 61.8 minutes, it remains limited to "at-rest attacks" targeting public keys already published on-chain, such as the 1.7 million BTC sitting in early Pay-to-Public-Key (P2PK) scripts.
Current Hardware Limits and Long-Term Protection
Despite the dramatic theoretical reduction in required hardware, existing quantum processors remain decades behind these thresholds. On October 20, Alice & Bob released results from the first phase of PROQCIMA—the French government’s quantum computing program—demonstrating a maximum chip size of just 12 qubits, which has not yet achieved error rates below the quantum correction threshold. Furthermore, the 29,588 qubit estimate relies on an assumed bit-flip lifetime of nearly a century; reducing that stability to one bit-flip per hour raises the required qubit count for RSA-2048 from 22,593 to roughly 45,000.
To counter future threats before hardware capabilities converge in the early 2030s, developer Jameson Lopp and five co-authors proposed BIP-361, a Bitcoin Improvement Proposal designed to freeze vulnerable legacy addresses in structured phases. As analysts evaluate long-term scenarios like Bitwise raising its 2036 Bitcoin price target, network security remains a central focus for institutional adoption, even as critics like Jason Calacanis face major bets after calling Bitcoin a dead network.
Key Takeaways
- New Benchmark: Alice & Bob estimates 29,588 cat qubits can crack a Bitcoin secp256k1 key in 61.8 minutes.
- Attack Types: The 61.8-minute duration prevents "on-spend" transaction hijacking, leaving only "at-rest" public keys—like 1.7 million BTC in legacy P2PK wallets—exposed.
- Hardware Gap: Current tests under France's PROQCIMA program only feature 12-qubit chips, far below the required scale.
- Mitigation: Developers have introduced BIP-361 to phase out and freeze quantum-vulnerable address formats ahead of predicted 2030s quantum maturity.
Why It Matters
This research highlights that while quantum computers are growing more efficient at breaking cryptographic primitives, practical risks to Bitcoin remain a decade away. Because Alice & Bob's 61.8-minute timeframe cannot beat Bitcoin's 10-minute block target, active transactions remain secure against real-time interception. The primary risk centers on unmigrated legacy coins, giving the Bitcoin developer community ample time to implement post-quantum upgrades like BIP-361 long before commercial quantum hardware reaches scale.
