Key Recovery Attacks on NTRU without Ciphertext Validation Routine

NTRU is an efficient public-key cryptosystem proposed by Hoffstein, Pipher, and Silverman. Assuming access to a decryption oracle, we show ways to recover the private key of NTRU systems that do not include a ciphertext validating procedure. The strongest of our methods will employ just a single call to the oracle, and in all cases, the number of calls needed will be small enough to be realistic.