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NTRU is a patented and open source public-key cryptosystem that uses lattice-based cryptography to encrypt and decrypt data. It consists of two algorithms: NTRUEncrypt, which is used for encryption, and NTRUSign, which is used for digital signatures. Unlike other popular public-key cryptosystems, it is resistant to attacks using Shor's algorithm and its performance has been shown to be significantly better. A proprietary for-pay implementation and an open source implementation of NTRU are available.
The first version of the system, which was called NTRU, was developed in 1996 by mathematicians Jeffrey Hoffstein (de), Jill Pipher, and Joseph H. Silverman. That same year, the developers of NTRU joined with Daniel Lieman and founded the NTRU Cryptosystems, Inc., and were given a patent on the cryptosystem. In 2009, the company was acquired by Security Innovation, a software security company.
At equivalent cryptographic strength, NTRU performs costly private key operations much faster than RSA. As key sizes increase, RSA's operations per second decrease cubicly, whereas NTRU's operations per second decrease quadratically.
According to the Department of Electrical Engineering, University of Leuven, "[using] a modern GTX280 GPU a throughput of up to 200 000 encryptions per second can be reached at a security level of 256 bits. Comparing this to a symmetric cipher (not a very common comparison), this is only around 20 times slower than a recent AES implementation."
Unlike RSA and Elliptic Curve Cryptography, NTRU is not known to be vulnerable to quantum computer based attacks. The National Institute of Standards and Technology wrote in a 2009 survey that "[there] are viable alternatives for both public key encryption and signatures that are not vulnerable to Shor’s Algorithm” and “[of] the various lattice based cryptographic schemes that have been developed, the NTRU family of cryptographic algorithms appears to be the most practical".