Quantum Public Key Encryption Scheme Enables Security on Current Noisy NISQ Devices

Quantum public key encryption represents a potentially revolutionary approach to secure communication, and researchers are now actively exploring its possibilities. Nishant Rodrigues from Microsoft Quantum, Walter O. Krawec from the University of Connecticut, and Brad Lackey from Microsoft Quantum, along with Deb Mukhopadhyay and Bing Wang, present a new encryption scheme designed specifically for today’s limited quantum computers. Unlike earlier proposals requiring substantial quantum processing power, this work achieves practical encryption using a small number of qubits and tolerates the noise inherent in current devices. The team’s design utilises classical public keys and ciphertexts, offering a crucial step towards realising quantum-resistant cryptography and opening doors to entirely new cryptographic systems beyond the reach of classical methods.

NISQ-Compatible Quantum Public-Key Encryption Demonstrated

Scientists have designed a practical public-key encryption scheme leveraging quantum pseudorandom functions, specifically tailored for current noisy intermediate-scale quantum (NISQ) devices. This work addresses a significant limitation of existing quantum PKE schemes, which typically require a large number of coherently operating qubits, impractical for today’s technology. The newly developed protocol relies on multiple, smaller groups of qubits in superposition, rather than a single, large coherent state, enabling implementation on existing hardware. Importantly, these qubit groups can be created sequentially, offering flexibility in deployment.

The team’s design supports classical error correction on the ciphertext while maintaining security, a crucial feature allowing the protocol to function even with noisy quantum public keys. This represents the first PKE scheme utilizing pseudorandom functions with this capability. Furthermore, the scheme offers a trade-off between efficiency and the number of qubits used in the public key, allowing for optimization as quantum computers become more reliable. Researchers demonstrated the protocol’s feasibility by designing and implementing circuits on the Quantinuum H1-1 computer. A rigorous security analysis, combining cryptographic hybrid arguments with quantum key distribution (QKD) style proof techniques, confirms the protocol’s robustness.

This analysis extends to scenarios with noisy public keys, a previously unaddressed aspect in recent PKE literature. The team’s work demonstrates that QKD security analyses can be broadly applicable to the design and security assessment of novel quantum cryptographic protocols, such as PKE. The design allows for sequential or parallel operation of qubit groups, enhancing scalability and adaptability to different quantum computing architectures. The researchers comprehensively modeled potential error sources affecting decryption, allowing them to estimate failure rates based on various parameters. This detailed analysis provides valuable insight into the practical limitations and achievable performance of the scheme. Future work may focus on extending the scheme to achieve complete CCA security, a standard benchmark for quantum public-key encryption. Furthermore, the researchers suggest their design, based on the Round-Robin Quantum Key Distribution (RR-QKD) protocol, could serve as a foundation for developing other quantum cryptographic tools beyond encryption.