TFHE Public-Key Encryption Revisited

Fully homomorphic encryption allows directly processing encrypted data without having to decrypt it. The result of the computation is encrypted, typically under the same key. This unique feature offers a strong form of privacy. A service provider can so provide the same service but without ever seeing the user’s data. Examples of application include [privacy-preserving] preventive medicine, facial recognition or voice assistants. Fully homomorphic encryption can also be used to solve the privacy issues of the blockchain. This paper introduces a public-key variant of fully homomorphic encryption scheme TFHE. The output ciphertexts are of LWE type and compatible with TFHE. Interestingly, the public key is much shorter and the resulting ciphertexts are less noisy. The security of the scheme holds under the standard RLWE assumption. Several variations and extensions are also described. The proposed scheme has been integrated in fhEVM, a protocol enabling developers to create encrypted on-chain smart contracts.