This library provides NTRU-based somewhat and leveled homomorphic encryption. The first option (leveled) is a single key LTV https://eprint.iacr.org/2014/039.pdf and the second option (flattened) is the former's flattened version https://eprint.iacr.org/2016/315.pdf
This library uses NTL (v9.0.2 or later) with GMP support (with C++11). It has been tested on Ubuntu 14.04 and Win10 environments.