A type of secure quantum communications protocol known as device-independent quantum key distribution (DI-QKD) uses peculiarities of quantum mechanics to generate its message-encryption keys. These keys can be shared by end users over public channels while remaining impervious to eavesdroppers, even over an untrusted network. Now, an analysis shows that one previously established requirement for DI-QKD—known as “Bell nonlocality”—fails to keep some DI-QKD protocols secure [1]. The team says that the finding could help researchers identify vulnerabilities in quantum encryption methods.

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