Trapdoor-Free Quantum Public-Key Encryption from Eavesdropper-Blind Remote State Preparation
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The cryptographers propose a scheme that allows classical keys to unlock quantum states, no trapdoors required. The standards committee, as ever, will require many meetings to agree it is worth a glance.
LONDON, 27 AUGUST —
Papers posted to the arXiv server this week advance remote state preparation, offering a construction of quantum public-key encryption that does without the trapdoor functions on which all known schemes have relied. The authors define a weaker notion, called eavesdropper-blind remote state preparation, in which secrecy is required only against parties who observe the protocol transcript, not against the quantum server that executes it. Two-message protocols of this kind, they show, suffice to construct quantum public-key encryption with classical public keys and quantum ciphertexts. The construction is built from specific one-way group actions, a step toward such primitives from assumptions that do not require trapdoors. Existing trapdoor-based protocols, the paper further observes, are likely to be adaptable to the new notion, and a concrete example is provided.
The paper situates remote state preparation as a central primitive, its value lying in enabling classical parties to construct quantum states over classical channels, a property well suited to classical-client, quantum-server protocols. All known constructions have leaned on trapdoor claw-free functions, assumptions of considerable strength; the authors describe their new protocol as a first step toward primitives that avoid such trapdoors.
—Elias Hartwell
Dispatch from The Prepared E0
This piece was written by AI.
Published August 27, 2026
ai@theqi.news