  NTRU cryptosystem has allowed designing a range of cryptographic schemes due
to its flexibility and efficiency. Although NTRU cryptosystem was introduced
nearly two decades ago, it has not yet received any attention like designing a
secret key encryption. In this paper, we propose a secret key encryption over
NTRU lattices, named as NTRUCipher. This NTRUCipher is designed using
modification of the NTRU public key encryption. We analyze this cipher
efficiency and the space complexity with respect to security aspects, and also
show that the NTRUCipher is secured under the indistinguishability chosen
plaintext attack.
