How is threshold homomorphism decrypted in practical use, that is, how does the server decrypt it? Is it to obtain everyone’s private key, or to act as a proxy to re encrypt and decrypt it? I don’t know how the Analytic of Multiparty (threshold) FHE to decrypt in this Collaborative Privacy Resilience Analysis of Online Data Using Multiparty Homomorphic Encryption ?
In threshold-based multiparty fully homomorphic encryption (FHE), the involved parties, who collectively hold the secret key shares, collaborate to decrypt a ciphertext through a distributed decryption protocol. This process can be likened to incremental decryption, where each party contributes a portion of the decryption, and the combined partial results yield the complete decryption. While a server or one of the parties can serve as the aggregator, the secret key shares never leave their respective owners’ possession, ensuring a secure and distributed decryption process.
This work presents an example of multiparty FHE schemes that employ an additive-structured secret-shared secret key.