libntruprime: Intro

libntruprime is a microlibrary for the Streamlined NTRU Prime cryptosystem. Streamlined NTRU Prime (`sntrup`) is a lattice-based cryptosystem with the following features:

- Stability: Almost all details of `sntrup` match a May 2016 publication. The only exceptions are small changes to encoding and hashing published in April 2019.
- Patent-freeness: April 2019 predates almost all post-quantum patents. Analyses of various lattice patents filed before April 2019 indicate no problems for `sntrup`.
- Deployment: The popular OpenSSH tool switched to `sntrup761` by default in April 2022, following initial integration of `sntrup` into TinySSH. `sntrup761` support then expanded into 15 SSH implementations, GitHub, etc., along with further applications such as PQConnect.
- Affordability: Keys and ciphertexts are about 1KB for `sntrup761`, and computations are fast.
- Careful design: Subject to the requirement of being a small lattice-based cryptosystem, `sntrup` is systematically designed to eliminate unnecessary complications in security review. It eliminates decryption failures, for example, and eliminates cyclotomics. The cryptosystem has never needed a security patch.
- Risk management: A much higher `sntrup1277` security level is fully supported, and is recommended whenever 2KB keys and ciphertexts are affordable, to reduce risks from improvements in lattice attacks.
- Flexibility: The `sntrup` design allows a full spectrum of tradeoffs between size and security level, so applications with intermediate size limits aren't forced into much lower security levels. Six different sizes have been selected for support.

libntruprime has a very simple stateless API based on the SUPERCOP API, with wire-format inputs and outputs, providing functions that directly match the KEM operations provided by the `sntrup` specification, such as functions

    sntrup1277_keypair
    sntrup1277_enc
    sntrup1277_dec

for the `sntrup1277` KEM.

Internally, libntruprime includes implementations designed to work portably across CPUs, and implementations designed for higher performance on Intel/AMD CPUs with AVX2 instructions. libntruprime includes automatic run-time selection of implementations.

libntruprime is intended to be called either by larger multi-function libraries (such as traditional cryptographic libraries) or directly by applications. This includes libraries and applications in other languages via FFI. The idea is that libntruprime takes responsibility for the details of `sntrup` computation, including optimization, timing-attack protection, and (in ongoing work) verification, freeing up the calling libraries and applications to concentrate on application-specific needs such as protocol integration.

If you're using Debian (starting with Debian 13) or Ubuntu (starting with Ubuntu 25.04), you can install libntruprime by typing `apt install libntruprime-dev -y` as root, and then jump straight into using the library. Alternatively, you can download and install the latest version of libntruprime from this site. You might also be interested in python-ntruprime, available in Debian and Ubuntu as `python3-ntruprime`; this provides a Python wrapper around libntruprime.

Latest release: 20260717.

Version: This is version 2026.07.17 of the "Intro" web page.