# Tag Info

12

The likelihood of a decryption failure can be made arbitrarily small. IEEE P1363.1 says in appendix A.4.10: For ternary polynomials with $d$ $+1$s and the same number of $-1$s, the chance of a decryption failure is given by [B30]: $$\operatorname{Prob}_{(q, d, N)}(\text{Decryption fails}) = P_{(d, N)} \left( \frac{q - 2}{6} \right)$$ where ...

5

I'm Chief Scientist at Security Innovation, which owns NTRU, and have contributed to the design of NTRUEncrypt and NTRUSign. The headline answer here is: NTRUEncrypt doesn't necessarily require decryption failures; it's a tradeoff you make, trading off key and ciphertext size against decryption failure probabilities. Parameter sets that don't give ...

4

That's not possible. It just so happens that this works with RSA because of the unique properties of RSA, but the majority of other asymmetric schemes just don't happen to work this way. For other schemes, the signature and encryption algorithms can be completely different and there may be no way to "encrypt" with the private key or "sign" with the public ...

3

$$(-10+22x+22x^3-22x^6) - 1 = -11+22x+22x^3-22x^6 \equiv 0 \mod 11.$$ When substracting a constant from a polynomial, you do not subtract it from every term, only from the constant term. If you need a refresher, see addition and subtraction of polynomials.

3

I'm Chief Scientist at Security Innovation, which acquired NTRU, and one of the co-authors of NTRUSign. The difference between NTRUEncrypt and NTRUSign is in how they use the lattice. All the NTRU algorithms are based on solving the Close Vector Problem in a particular form of lattice known as an "ideal lattice". For NTRUEncrypt, the encryption method is ...

2

Reducing mod 3 means indeed reducing each coefficient mod 3, and again we choose the representatives symmetrically around 0, so each coefficient becomes -1,0 or 1 (instead of, which is also possible, 0,1, and 2, or some other choice). $-7X$ becomes $-X$ because $-7 \equiv -1 \mod 3$. The starting constant 3, becomes 0, and disappears, $-10X^2$ becomes ...

2

The open source version of CyaSSL contains code that calls into the commercial NTRU library -- the library itself is missing of course. You might be able to make CyaSSL work with the open source NTRU implementation at https://github.com/tbuktu/libntru ; it's alpha level software though.

2

One reason why it won't work that I can think of is because NTRU encryption is probabilistic, so the encrypted message is not unique for a given plaintext. There is a signature scheme named NTRUSign which is described in Digital Signatures Using the NTRU Lattice. A Java implementation of NTRUSign exists at https://github.com/tbuktu/ntru. Edit: Yes, ...

1

"how $-10+22X+22X^3-22X^6$ may be 1 (modulo 11) if 22 = 0 mod 11?" Because when you reduce this mod 11 you get $$1 + 0 X + 0 X^3 + 0 X^6 = 1.$$ You seem to think that saying a polynomial is 1 mod 11 means that all its terms are 1 mod 11. What it actually means is that the constant term is 1 mod 11, and all the other terms are 0.

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