Skip to content


Repository files navigation


Build Status Coverage Status

This repository contains the official reference implementation of the Kyber key encapsulation mechanism, and an optimized implementation for x86 CPUs supporting the AVX2 instruction set. Kyber has been selected for standardization in round 3 of the NIST PQC standardization project.

Build instructions

The implementations contain several test and benchmarking programs and a Makefile to facilitate compilation.


Some of the test programs require OpenSSL. If the OpenSSL header files and/or shared libraries do not lie in one of the standard locations on your system, it is necessary to specify their location via compiler and linker flags in the environment variables CFLAGS, NISTFLAGS, and LDFLAGS.

For example, on macOS you can install OpenSSL via Homebrew by running

brew install openssl

Then, run

export CFLAGS="-I/usr/local/opt/openssl@1.1/include"
export NISTFLAGS="-I/usr/local/opt/openssl@1.1/include"
export LDFLAGS="-L/usr/local/opt/openssl@1.1/lib"

before compilation to add the OpenSSL header and library locations to the respective search paths.

Test programs

To compile the test programs on Linux or macOS, go to the ref/ or avx2/ directory and run


This produces the executables


where $ALG ranges over the parameter sets 512, 768, 1024, 512-90s, 768-90s, 1024-90s.

  • test_kyber$ALG tests 1000 times to generate keys, encapsulate a random key and correctly decapsulate it again. Also, the program tests that the keys cannot correctly be decapsulated using a random secret key or a ciphertext where a single random byte was randomly distorted in order to test for trivial failures of the CCA security. The program will abort with an error message and return 1 if there was an error. Otherwise it will output the key and ciphertext sizes and return 0.
  • test_kex$ALG tests the authenticated key exchange schemes derived from the Kyber KEM
  • test_vectors$ALG generates 10000 sets of test vectors containing keys, ciphertexts and shared secrets whose byte-strings are output in hexadecimal. The required random bytes come from a simple deterministic expansion of a fixed seed defined in test_vectors.c.

Benchmarking programs

For benchmarking the implementations, we provide speed test programs for x86 CPUs that use the Time Step Counter (TSC) or the actual cycle counter provided by the Performance Measurement Counters (PMC) to measure performance. To compile the programs run

make speed

This produces the executables


for all parameter sets $ALG as above. The programs report the median and average cycle counts of 1000 executions of various internal functions and the API functions for key generation, encapsulation and decapsulation. By default the Time Step Counter is used. If instead you want to obtain the actual cycle counts from the Performance Measurement Counters, export CFLAGS="-DUSE_RDPMC" before compilation.

Please note that the reference implementation in ref/ is not optimized for any platform, and, since it prioritises clean code, is significantly slower than a trivially optimized but still platform-independent implementation. Hence benchmarking the reference code does not provide meaningful results.

Our Kyber implementations are contained in the SUPERCOP benchmarking framework. See here for cycle counts on an Intel KabyLake CPU.

Shared libraries

All implementations can be compiled into shared libraries by running

make shared

For example in the directory ref/ of the reference implementation, this produces the libraries


for all parameter sets $ALG, and the required symmetric crypto libraries

All global symbols in the libraries lie in the namespaces pqcrystals_kyber$ALG_ref, libpqcrystals_aes256ctr_ref and libpqcrystals_fips202_ref. Hence it is possible to link a program against all libraries simultaneously and obtain access to all implementations for all parameter sets. The corresponding API header file is ref/api.h, which contains prototypes for all API functions and preprocessor defines for the key and signature lengths.


Also available is a portable cmake based build system that permits building the reference implementation.

By calling

mkdir build && cd build && cmake .. && cmake --build . && ctest

the Kyber reference implementation gets built and tested.