BTQ Technologies has recently published A quantum algorithm for one-shot signatures, the first circuit-level implementation of a new kind of cryptographic primitive, one whose single-use security is enforced not by trust or consensus but by the laws of quantum mechanics. The new system addresses a vulnerability in existing digital signatures which rely on the hardness of problems like factoring large integers, a weakness Shor’s algorithm threatens with quantum computers.
Unlike traditional signatures using two mathematically related keys, this scheme creates a signature verifiable with a public key but designed for one-time use only; as the company explains, it offers security “enforced not by trust or consensus but by the laws of quantum mechanics.” This approach allows for secure delegation of signing authority for a finite number of actions without the risk of key duplication.
BTQ Technologies’ Quantum Algorithm for One-Shot Signatures
BTQ Technologies detailed an implementation of a one-shot signature scheme, translating abstract cryptographic procedures into explicit quantum circuits as described in their paper, “A Quantum Algorithm for One-Shot Signatures.” This circuit-level version generates a classical public key alongside a quantum signing key, a quantum state, and utilizes a superposition over a hidden affine subspace to create the key. The signing process involves processing and measuring this quantum state to produce a classical signature, verifiable by anyone possessing the corresponding public key.
The underlying construction relies on a quantum secret key existing as a superposition over a hidden, shifted grid within a large space of binary strings; signing is achieved through a reflection of this grid. While prior work established the theoretical possibility and security of one-shot signatures, BTQ Technologies’ contribution lies in specifying the detailed quantum circuits necessary for practical implementation.
The team’s research estimates the number of logical qubits and quantum gates required, scaling with the desired security level of the scheme, and currently exists as a pre-obfuscation implementation, the company says. These classical methods are increasingly vulnerable as quantum computers advance, particularly due to algorithms like Shor’s algorithm. The team’s work builds on a foundation of theoretical exploration, including Scott Aaronson’s investigations into “Quantum Copy-Protection and Quantum Money” and subsequent research on “Quantum Money from Hidden Subspaces” with Paul Christiano.
Mark Zhandry’s work, detailed in “Quantum Lightning Never Strikes the Same State Twice,” further informed the development of this new signature scheme. Omri Shmueli and Zhandry’s 2025 paper, “On One-Shot Signatures, Quantum vs Classical Binding, and Obfuscating Permutations,” provided critical context for the current implementation. The researchers made the full details of their quantum algorithm available on arXiv, inviting further scrutiny and collaboration.
Digital Signatures & Cryptographic Primitives Explained
Traditional digital signatures authenticate messages and verify data integrity, playing a critical role in securing software updates and financial transactions, but their security often rests on computational hardness assumptions; the belief that certain mathematical problems, such as factoring very large integers, cannot be solved efficiently. While Shor discovered ways to use quantum computers to factor large numbers and break commonly used elliptic curve digital signatures, new post-quantum cryptography makes protocols secure against even quantum computers.
BTQ Technologies’ system explores an alternative path, using quantum computing to establish entirely new cryptographic capabilities, according to the company. The core innovation lies in the creation of a signature (σ) using a secret key, which, after verification with the corresponding public key, is irrevocably destroyed. While earlier work established the theoretical foundations, this circuit-level version provides a concrete pathway toward potential integration with existing cryptographic infrastructure.
Delegating Authority with Reusable vs. One-Shot Keys
Delegating authority with reusable versus one-shot keys presents distinct security profiles, and BTQ Technologies has demonstrated a circuit-level implementation exploiting the ephemeral nature of quantum states for single-use signatures. Unlike conventional cryptographic keys permitting repeated use, this system uses quantum mechanics to ensure a key is rendered unusable after signing a single message, preventing unauthorized duplication of signing power. Bob, receiving delegated authority, first generates a one-shot public key and a corresponding quantum secret key, establishing a temporary signing capability.
This approach addresses a specific vulnerability in traditional digital signatures, which rely on the difficulty of solving certain mathematical problems, a reliance threatened by the advent of quantum computing. Alice, the original authority, then employs her existing reusable digital signature key to endorse Bob’s one-shot public key, creating a certificate of authorization before Bob utilizes his fragile quantum key to sign a single, designated update.
Charlie, the verifier, then confirms both Alice’s conventional signature on Bob’s public key and Bob’s one-shot signature on the update, requiring only classical computational resources for verification. BTQ Technologies’ implementation is specifically designed for pre-obfuscation, meaning the circuits are prepared before any attempt at interference or copying. “We show how to prepare the affine subspace state, implement the required reflections and measurements,” the researchers report, highlighting the concrete steps taken to realize this quantum signature scheme.
The team’s work builds on the principle that quantum mechanics makes the signing key fragile and impossible to copy perfectly, while computational hardness prevents adversaries from generating equivalent keys. This isn’t simply about protecting existing classical cryptography from quantum attacks; it’s about creating an entirely new cryptographic capability with unique functionality, security, and privacy features, as the team explains.
While strong post-quantum cryptographic schemes focus on classical algorithms resistant to quantum computers, one-shot signatures offer a fundamentally different approach. The system’s design ensures that using the key to sign one message causes its self-destruction, preventing Bob from signing additional messages on Alice’s behalf. The long storage requirement for the quantum secret key is particularly well-suited to neutral-atom processors, offering a stable platform for maintaining the delicate quantum state until it is consumed for signing.
Quantum State Key Generation and Measurement Process
This process moves beyond simply storing a bit string; it creates a fragile quantum state on a quantum processor, fundamentally altering how cryptographic keys are produced and secured. This fragility mirrors the behavior described in the Schrödinger’s cat thought experiment, where measurement irreversibly alters the system’s state; opening the box forces a definite outcome, destroying the initial superposition. BTQ Technologies’ approach uses this principle, combined with the no-cloning theorem, to ensure the signing key is effectively destroyed after a single use.
Scott Aaronson’s earlier work on quantum money and copy protection provided a foundation for preventing the creation of multiple valid quantum signing keys from a single generation procedure. His complexity-theoretic no-cloning theorem builds on the physical no-cloning principle by establishing computational limits on replicating quantum states, even for an adversary with access to the key generation process.
Mark Zhandry further refined this concept with a storm algorithm that generates signing keys, or “bolts”, with the guarantee that no two bolts will share the same public key; “lightning may strike anywhere, but it will never strike the same place twice.” The team detailed in A quantum algorithm for one-shot signatures how to translate these abstract concepts into concrete quantum circuits.
No-Cloning Theorem Prevents Quantum Key Replication
The inability to perfectly replicate an unknown quantum state, formalized by the no-cloning theorem, underpins the security of a new cryptographic scheme developed by BTQ Technologies, preventing the unauthorized duplication of digital signatures. While classical information can be copied without limit, quantum information presents a fundamental barrier to perfect replication, a principle used to create keys that are inherently fragile and unusable beyond a single transaction.
This work, alongside refinements by Mark Zhandry, laid the groundwork for one-shot signatures, where the key’s very existence is tied to a single use. The system’s design prevents an adversary from generating multiple valid signing keys associated with the same public key, as any attempt to duplicate the quantum state will inevitably introduce errors, rendering the copied key unusable. “If Bob has access to the key-generation procedure, what prevents him from running it twice?” the researchers ask, highlighting the problem their system solves.
The solution lies in the combination of quantum fragility and computational hardness, ensuring that the key self-destructs after signing a single message. Instead, security stems directly from the laws of physics, offering a fundamentally different level of assurance.
As the researchers explain, this is “not only quantum key distribution, and it is not only the replacement of RSA with a quantum-resistant classical algorithm,” but a new paradigm for cryptographic capabilities made possible by quantum information. The long-term goal is to build cryptographic systems that use these quantum properties on near-term hardware, expanding the possibilities beyond simply protecting existing systems from quantum threats.
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