Chosen-Ciphertext Attacks on Optimized NTRU

NTRU([3]) is an efficient public-key cryptosystem proposed by Hoffstein, Pipher, and Silverman. In [4], some modifications were made to the original scheme to make the system even faster. We give three chosenciphertext attacks on the un-padded version of this optimized NTRU cryptosystem. Any one of the three attacks will recover the private key with just a few queries to the decryption machine.