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arXiv:2605.03564

Quantum Vault: Secure Token Authentication Without Classical State Information Benchmarked on IBMQ

Lucas Tsunaki, Boris Naydenov

quant-phSubmitted May 5, 2026• Announced May 6, 2026• 0 citations
v1 · May 5, 2026v2 · Sep 14, 2026
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Abstract

Quantum tokens are underlying primitives for quantum money and network proposals, which leverage the no-cloning theorem to realize unforgeable authentication. A relevant but overlooked type of attack to such architectures is a hacker that steals the classical side information of the token states from the issuing agent (e.g. a bank), allowing the forgery of fake tokens without violating no-cloning theorem. Our proposal avoids this threat by removing classical side information about the token states, where instead a copy of the token is stored at the bank, i.e. a quantum vault. This copy can be accessed by anyone to perform authentication, consuming the token pair in the process. Our protocol is benchmarked and quality parameters are identified within a hardware agnostic framework employing three cloud-based IBM quantum (IBMQ) processors, such that the protocol is applicable to arbitrary quantum platforms. By comparing the efficiency with which genuine tokens are produced and authenticated with a possible query attack scenario, we demonstrate the security of the protocol. Where we achieve probabilities lower than $10^{-4}$ for false-negative errors and $10^{-18}$ for successful attacks when considering quantum bills composed of 200 tokens, even in the worst performing hardware. The quantum vault not only symmetrically protects both user and bank with the same quantum principles, but provides a step towards public key authentication, since any untrusted party can have authentication access granted from the bank to the tokens without being able to clone them, assuming they have a quantum channel with the vault. Besides public accessible verifiability, our proposal naturally achieves standard unforgeability, traceability and revocability.

Comments
11 pages, 5 figures

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Quantum tokens are underlying primitives for quantum money and network proposals, which leverage the no-cloning theorem to realize unforgeable authentication. A relevant but overlooked type of attack to such architectures is a hacker that steals the classical side information of the token states from the issuing agent (e.g. a bank), allowing the forgery of fake tokens without violating no-cloning theorem. Our proposal avoids this threat by removing classical side information about the token states, where instead a copy of the token is stored at the bank, i.e. a quantum vault. This copy can be accessed by anyone to perform authentication, consuming the token pair in the process. Our protocol is benchmarked and quality parameters are identified within a hardware agnostic framework employing three cloud-based IBM quantum (IBMQ) processors, such that the protocol is applicable to arbitrary quantum platforms. By comparing the efficiency with which genuine tokens are produced and authenticated with a possible query attack scenario, we demonstrate the security of the protocol. Where we achieve probabilities lower than 10−410^{-4}10−4 for false-negative errors and 10−1810^{-18}10−18 for successful attacks when considering quantum bills composed of 200 tokens, even in the worst performing hardware. The quantum vault not only symmetrically protects both user and bank with the same quantum principles, but provides a step towards public key authentication, since any untrusted party can have authentication access granted from the bank to the tokens without being able to clone them, assuming they have a quantum channel with the vault. Besides public accessible verifiability, our proposal naturally achieves standard unforgeability, traceability and revocability.
Abstract Quantum tokens are underlying primitives for quantum money and network proposals, which leverage the no-cloning theorem to realize unforgeable authentication. A relevant but overlooked type of attack to such architectures is one in which a hacker steals the classical side information about the token states from the issuing agent (e.g., a bank), enabling the forgery of fake tokens without violating the no-cloning theorem. Our proposal addresses this threat by removing the classical side information about the token states, where instead a copy of the token is stored at the bank, i.e. a quantum vault. This copy can be accessed by anyone to perform authentication, consuming the token pair in the process. We benchmark the protocol and identify quality parameters within a hardware agnostic framework employing IBM Quantum processors, such that the protocol is applicable to arbitrary quantum platforms. By comparing the efficiency with which genuine tokens are produced and authenticated against a possible estimate-and-forge attack, we quantify the security of the protocol. We achieve probabilities lower than 10-4 for false-negative errors (Type 1) and 10-10 for successful attacks (Type 2) when considering quantum bills composed of 200 tokens, even in the worst performing processor and a conservative uncertainty estimate. The quantum vault not only protects both user and bank symmetrically with the same quantum principles, but provides a step towards public key authentication, since any untrusted party can have access granted by the bank to the tokens' authentication interface without being able to clone them. Besides this bank-mediated form of publicly accessible verifiability, our proposal achieves traceability and revocability, since the bank retains the vault copy of the tokens.
Quantum tokens envision to store unclonable quantum states in a physical device, with the goal of being used for personal authentication protocols, as required by banks. Still, the experimental realization of such devices faces many technical challenges, which can be partially mitigated using ensembles instead of single qubits. In this work, we thus propose an ensemble-based quantum token protocol, describing it through a simple yet general model based on a quantum mechanical observable. The protocol is benchmarked on five IBM quantum processors and a general hacker attack scenario is analyzed, in which the attacker attempts to read the bank token and forge a fake one, based on the information gained from this measurement. We experimentally demonstrate that the probability that the bank erroneously accepts a forged coin composed of multiple tokens can reach values below 10−2210^{-22}10−22, while the probability that the bank accepts its own coin is above 0.999. The overall security of the protocol is therefore demonstrated within a hardware-agnostic framework, confirming the practical viability of the protocol in arbitrary quantum systems and thus paving the way for future applications with different ensembles of qubits, such as color center defects in solids.
Abstract Quantum tokens envision to store unclonable quantum states in a physical device, with the goal of being used for personal authentication protocols, as required by banks. Still, the experimental realization of such devices faces many technical challenges, which can be partially mitigated using ensembles instead of single qubits. In this work, we thus propose an ensemble-based quantum token protocol, describing it through a simple yet general model based on a quantum mechanical observable. The protocol is benchmarked on five IBM quantum processors and a general hacker attack scenario is analyzed, in which the attacker attempts to read the bank token and forge a fake one, based on the information gained from this measurement. We experimentally demonstrate that the probability that the bank erroneously accepts a forged coin composed of multiple tokens can reach values below 10−22, while the probability that the bank accepts its own coin is above 0.999. The overall security of the protocol is therefore demonstrated within a hardware-agnostic framework, confirming the practical viability of the protocol in arbitrary quantum systems and thus paving the way for future applications with different ensembles of qubits, such as color center defects in solids.
Forty years ago, Wiesner proposed using quantum states to create money that is physically impossible to counterfeit, something that cannot be done in the classical world. However, Wiesner's scheme required a central bank to verify the money, and the question of whether there can be unclonable quantum money that anyone can verify has remained open since. One can also ask a related question, which seems to be new: can quantum states be used as copy-protected programs, which let the user evaluate some function f, but not create more programs for f? This paper tackles both questions using the arsenal of modern computational complexity. Our main result is that there exist quantum oracles relative to which publicly-verifiable quantum money is possible, and any family of functions that cannot be efficiently learned from its input-output behavior can be quantumly copy-protected. This provides the first formal evidence that these tasks are achievable. The technical core of our result is a "Complexity-Theoretic No-Cloning Theorem," which generalizes both the standard No-Cloning Theorem and the optimality of Grover search, and might be of independent interest. Our security argument also requires explicit constructions of quantum t-designs. Moving beyond the oracle world, we also present an explicit candidate scheme for publicly-verifiable quantum money, based on random stabilizer states; as well as two explicit schemes for copy-protecting the family of point functions. We do not know how to base the security of these schemes on any existing cryptographic assumption. (Note that without an oracle, we can only hope for security under some computational assumption).
The realization of devices that harness the laws of quantum mechanics represents an exciting challenge at the interface of modern technology and fundamental science. An exemplary paragon of the power of such quantum primitives is the concept of “quantum money” [Wiesner S (1983) ACM SIGACT News 15:78–88]. A dishonest holder of a quantum bank note will invariably fail in any counterfeiting attempts; indeed, under assumptions of ideal measurements and decoherence-free memories such security is guaranteed by the no-cloning theorem. In any practical situation, however, noise, decoherence, and operational imperfections abound. Thus, the development of secure “quantum money”-type primitives capable of tolerating realistic infidelities is of both practical and fundamental importance. Here, we propose a novel class of such protocols and demonstrate their tolerance to noise; moreover, we prove their rigorous security by determining tight fidelity thresholds. Our proposed protocols require only the ability to prepare, store, and measure single quantum bit memories, making their experimental realization accessible with current technologies.
The no-cloning theorem can be used as a basis for quantum money constructions which guarantee unconditionally unforgeable currency. Existing schemes, however, either (i) require long-term quantum memory and quantum communication between the user and the bank in order to verify the validity of a bill or (ii) fail to protect user privacy due to the uniqueness of each bill issued by the bank, which can allow its usage to be tracked. We introduce a construction of single-use quantum money that gives users the ability to detect whether the issuing authority is tracking them, employing an auditing procedure for which we prove unconditional security. Bill validation is classical, and hence does not require long-term quantum memory or quantum communication, making the protocol relatively practical to deploy. We discuss potential applications beyond money, including anonymous one-time pads and voting.