1. A computing device comprising: one or more processing devices; and one or more computer-readable memories or storage devices storing instructions which, when executed by the one or more processing devices, configure the one or more processing devices to: generate a key using a fully homomorphic encryption technique; generate a modifier factor; encrypt a first input using the key to obtain a first ciphertext; send the first ciphertext and the modifier factor to a server that performs a multi-party computation using the first ciphertext, the modifier factor, and a second ciphertext provided by a second computing device to obtain an encrypted output, the use of the modifier factor not revealing the key to the server; receive the encrypted output from the server; and decrypt the encrypted output, the use of the modifier factor in the multi-party computation influencing a degree of an underlying polynomial function used to decrypt the encrypted output.