# In NTRU digital envelope, do everyone know the hash function $H$ used?

I have a simple question about the NTRU original cryptosystem using a digital envelope.

The article can be found here: http://grouper.ieee.org/groups/1363/lattPK/submissions/ntru.pdf

It is said that we need a generating function $G$ and a hash function $H$.

Suppose that Alice wants to send a message to Bob. Then she will use some generating function $G$ and some hash function $H$.

Bob recieves the ciphertext $e$ and at a certain point of decryption it is said that Bob should compare $c''$ and $H(c',b)$.

Suppose that Eve exists.

My question is: Do Bob and Eve know $G$ and $H$? In the way the decryption is described, Bob needs to know $H$, but it's not clear if he knows it.

Thanks in advance.

## 1 Answer

Yes, these are public parameters of the system.

Note that NTRU is not implemented exactly this way any more. The most up-to-date current spec is EESS#1, which can be obtained from https://github.com/NTRUOpenSourceProject/ntru-crypto/blob/master/doc/EESS1-v3.1.pdf.

• Thanks a lot. I am aware of the more recent implementation of NTRU, I'm just starting from its origins Jul 23 '16 at 21:20