Cracking the Code: Quantum Circuit Splitting Isn’t Secure

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Author: Denis Avetisyan

A new attack demonstrates that techniques designed to protect quantum circuit designs from reverse engineering are surprisingly vulnerable.

A security vulnerability exists where an attacker can reverse-engineer hidden qubit connections within a quantum circuit designed with split compilation by strategically querying the deployed circuit’s input-output behavior.
A security vulnerability exists where an attacker can reverse-engineer hidden qubit connections within a quantum circuit designed with split compilation by strategically querying the deployed circuit’s input-output behavior.

Researchers have shown that an oracle-guided attack can efficiently reconstruct original quantum circuits even when split for intellectual property protection, challenging the security of this compilation method.

Protecting quantum circuit intellectual property is crucial as quantum computing advances, yet existing obfuscation techniques lack rigorous security evaluations. This paper, ‘Security Evaluation of Quantum Circuit Split Compilation under an Oracle-Guided Attack’, investigates the resilience of split compilation—a common obfuscation method—against a novel, efficient attack. We demonstrate that an oracle-guided approach can reconstruct obfuscated circuits with far fewer input-output queries than previously anticipated, revealing a significant vulnerability. Does this necessitate a re-evaluation of current quantum IP protection strategies and the development of more robust defenses?

The Fragility of Quantum Designs

Quantum algorithms, including Grover’s and the Quantum Approximate Optimization Algorithm, drive demand for quantum computing resources. Designing secure quantum circuits presents challenges, leaving designs vulnerable to reverse engineering and intellectual property theft. Classical circuit obfuscation techniques are inadequate for quantum systems. Protecting these designs is paramount; novel security approaches tailored to quantum architectures are therefore critical. A quantum design’s inherent fragility underscores that true power lies in what remains hidden.

Decomposition as Obfuscation

Split compilation protects quantum circuit intellectual property by fragmenting larger circuits into subcircuits, complicating reverse engineering. Techniques like randomized reversible subcircuits and quantum logic locking further enhance obfuscation. However, recent analysis reveals split compilation is vulnerable to attack with oracle queries increasing linearly with split depth – a significant reduction in security compared to previously assumed exponential complexity. Phase obfuscation adds complexity but doesn’t address this fundamental vulnerability.

Reassembling the Quantum Puzzle

The Hierarchical Reconstruction Algorithm addresses the challenge of reassembling split quantum circuits. It systematically reconstructs the original circuit layer by layer, leveraging inherent quantum properties. Its efficiency relies on gate reversibility and block elimination, reducing the search space for circuit connectivity and enabling scalable reconstruction. Testing has been performed on Qiskit, Amazon Braket, IBM Quantum, and Microsoft Azure. Successful reconstruction requires accurate qubit mapping and stringent single-wire consistency checks, with a noise threshold of 0.03 to differentiate noise from mapping errors. Benchmarking against the RevLib library provides a standardized performance evaluation framework.

Validating Quantum Integrity

Connection Restoration confirms accurate subcircuit linkage in reconstructed quantum circuits, ensuring overall functionality. Failure to restore connections introduces errors invalidating the reconstruction. Input-Output Behavior analysis and Oracle Access validate a circuit’s functionality by comparing its output to known results and verifying it against a trusted external source. This verification safeguards against manipulation and unintentional errors. Demonstrations of this reconstruction technique highlight ongoing challenges in scaling and efficiency; random circuit sampling on Google’s Willow processor took under 5 minutes – a computation estimated to require 10 septillion years for classical supercomputers, testament to quantum progress and the path to practical quantum advantage.

The study illuminates a fundamental fragility within ostensibly secure systems. The attempted shielding of quantum circuit designs through splitting proves, under scrutiny, to be a reduction in complexity that does not equate to true security. As Albert Einstein observed, “It does not require a majority to be correct; only a single mind.” This holds true for the oracle-guided attack; a focused, intelligent query—a single ‘mind’—efficiently dismantles the layered obfuscation intended to protect intellectual property. The hierarchical reconstruction, though designed as a barrier, merely presents a structured path for determined analysis, a testament to the illusion of security through complexity.

What’s Next?

The demonstrated vulnerability of circuit splitting to oracle-guided attacks necessitates a reassessment of its protective capabilities. The pursuit of obfuscation, it seems, merely shifts the difficulty—not eliminates it. Future work must move beyond attempts to increase query complexity. Such endeavors invite diminishing returns, a familiar pattern. The focus should instead be on fundamentally altering the attack surface.

Hierarchical reconstruction, as highlighted, presents a critical pathway for adversaries. Research into circuit transformations that actively disrupt this process – perhaps introducing controlled irreversibility, or strategically embedding decoherence – may prove fruitful. However, any such measure will inevitably introduce performance overhead. The challenge lies in minimizing this cost while maximizing the disruption to reverse engineering efforts. A clear articulation of acceptable trade-offs is paramount.

Ultimately, the problem is not simply one of technical sophistication. It is one of information. Security, in this context, is not about preventing access, but about raising the cost of meaningful interpretation. Clarity is the minimum viable kindness; but for intellectual property, perhaps a degree of controlled opacity is justified. The question remains: how much?

Original article: https://arxiv.org/pdf/2511.04842.pdf

Contact the author: https://www.linkedin.com/in/avetisyan/

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2025-11-10 13:06