Quantum cryptography hybrid confidential computing

This invention provides an architecture that enables quantum confidential computing across different cryptographic systems within a single session, without decryption, by linking the keys used in Fully Homomorphic Encryption (FHE) and Quantum Homomorphic Encryption (QHE).

Problem addressed: Until now there has been no way to confirm that an FHE ciphertext and a quantum encrypted state belong to the same processing session without decrypting their contents. If data from two different sessions is combined, the computation still returns a result, and the error cannot be detected afterwards. Decrypting in order to check would destroy the very confidentiality the system exists to protect.

Approach: An integrity tag is derived from identifiers held on both the classical side and the quantum side, and that tag is verified before any quantum computation result is accepted. No plaintext and no secret key is used at any point in the verification. If the verification fails, the quantum computation result is discarded and the quantum state is erased, so a mismatched result can never propagate downstream. The specific derivation and the way the identifiers are combined are disclosed to interested partners under NDA.

Effect: Classical computation under FHE and quantum computation under QHE can be operated as a single confidential computing process. The data stays encrypted from end to end, and the operator of the quantum computing resource never sees the content it is processing.

Applications: Post-quantum cloud confidential computing, in particular finance (credit assessment and transaction screening carried out on encrypted customer data) and healthcare (analysis carried out on encrypted patient records), and any setting where computation must be outsourced to a third-party quantum resource.

Status: Patent application filed in Japan. The application contains three independent claims covering the system, the method, and the program. Not yet laid open.