I have come across this paper On-the-fly multiparty computation via on-the-cloud Multikey from Fully Homomorphic Encryption by Lopez-Alt et al., where authors describe a NTRU-based homomorphic encryption scheme suitable for a multikey context. Multikey means each party encrypts its input with its unique key, the server computes homomorphically some evaluations and in the final stage, parties run an MPC protocol for decryption.
I have not understood this phase yet and I can imagine two ways to do it :
compute the NTRU decryption as a function by a MPC protocol
prove that NTRU homomorphic encryption scheme can be used to build a threshold homomorphic encryption scheme following the template from Multiparty Computation with Low Communication, Computation and Interaction via Threshold FHE by Asharov et al., namely, replacing the BGV scheme with the NTRU homomorphic encryption scheme.
What is the correct implementation ?