This thesis introduces how the NTRU cryptosystem works and an elementary cryptanalysis about lattice. After ntroducing NTRU, we briefly describe the lattice structure and LLL, the lattice reduction algorithm from a cryptanalytic point of view, and then express the relations between NTRU and the lattice structure. Finally, we extend the system by adjusting the key space, parameters and message space with appropriate restrictions to endow NTRU encryption with various properties of ring homomorphism.
