Multi-key Fully-Homomorphic Encryption in the Plain Model

The notion of multi-key fully homomorphic encryption (multi-key FHE) [Lopez-Alt, Tromer, Vaikuntanathan, STOC’12] was proposed as a generalization of fully homomorphic encryption to the multiparty setting. In a multi-key FHE scheme for n parties, each party can individually choose a key pair and use it to encrypt its own private input. Given n ciphertexts computed in this manner, the parties can homomorphically evaluate a circuit C over them to obtain a new ciphertext containing the output of C, which can then be decrypted via a decryption protocol. The key efficiency property is that the size of the (evaluated) ciphertext is independent of the size of the circuit.