The submission for LESS contains the following:

• Reference_Implementation

A reference implementation of the signature LESS as a C99 library. The reference implementation library does not provide a main() function, and is intended to be compiled and linked to a binary. The required NIST API is present in Reference_Implementation/include/api.h. The implementation employ a provided generic keccak implementation.

• Optimized_Implementation

We provide multiple different optimized versions of the LESS signature scheme. In total we provide two different optimized implementation: an AVX2, NEON. The AVX2 version is optimized for modern Intel CPUs from the Haswell generation. The NEON version is optimized for ARM CPUs like Apple M1.

The library is organized in the same fashion as the reference one, except there is no support for using libkeccak. All implementations come with their own optimized SHA3 and SHAKE implementation.

The following libraries/tools are needed:

• cmake
• make
• gcc/clang
• openssl
• pkg-config

Utilities

This directory provides CMake based building facilities to generate executable files either performing a benchmark of LESS, or generating the Known Answer Test files in the KAT folder, as well as a script used for parameter generation.

Benchmarking:

To build the benchmarking binaries, run the following:

cd Utilities/Benchmarking
mkdir build && cd build
cmake .. 
make 

1 - Enter Utilities/Benchmarking 2 - create a "build" directory and enter it 3 - type cmake ../ to generate the makefiles 4 - type make to compile the codebase

By default, the optimized AVX2 implementation will be compiled. To select the reference implementation for building, add -DUSE_REFERENCE=1 to the cmake command in step 3. To enable the ARM neon implementation you need to add a -DUSE_NEON=1.

Once build you can either run each binary like:

./LESS_benchmark_cat_252_45

or you can use the bench.sh script, which will automatically generate a markdown table with the results. Additionally you can pass the flag -DUSE_SANITIZER=1 to the cmake command to check for memory errors. Note, this slows the program down.

NOTE: If you run the benchmarks on an ARM based Apple computer, make sure that you run the binaries/scripts with root rights.

KAT Generation:

The KAT_Generation directory is organized in the same fashion as the Benchmarking one. The same compilation procedure enacted for the benchmarking binary will generate all the executable files needed to re-generate the Known Answer Tests files. Specifically,

cd Utilities/KAT_Generation
mkdir build && cd build
cmake .. 
make 

By default, the reference implementation will be compiled. To select the optimized implementation for building, add either

-DUSE_AVX2=1
-DUSE_NEON=1
-DUSE_REFERENCE=1

to the command in step 3. Only ever add one of the targets. The standard is to use the reference implementation. Additionally, you can also enable a debug build by adding -DCMAKE_BUILD_TYPE=Debug to the command in step 3. Furthermore you can add -DUSE_SANITIZE=1 to enable memory/pointer sanitation.

A commodity script generating all KATs is provided: gen_all_kat.sh. It can be run without parameters. KATs will be generated in the KAT directory

NOTE: If you are on a apple system: make sure that you use clang, by appending -DCMAKE_C_COMPILER=clang. Otherwise LESS will most likely not build in debug mode, due to missing support for the address sanitizer.