An implementation of the SCloud+ KEM in Jasmin

This repository contains an implementation in Jasmin of the SCloud+ KEM (https://eprint.iacr.org/2024/1306). The code is based on the C implementation available from https://github.com/scloudplus/scloudplus.

Some remarks on this implementation

Differences wrt the C implementation

We diverge from the C implementation in a couple of implementation choices. Specifically,

1. serialisation strategy of the ciphertext;
2. the sampling of ternary secrets ($\Phi$ and $\Psi$ algorithms).

Jasmin compiler version

To compile the Jasmin code, a development version of the Jasmin compiler (jasminc) with limited support for floating-point instructions is required. For convenience, the required version is provided as a submodule (submodules/jasmin). Instructions for building the toolset are available at https://jasmin-lang.readthedocs.io/en/stable/misc/installation_guide.html#install-the-jasmin-tools.

Keccak library

We rely on the Jasmin library of the SHA3 family of hash functions available from git@github.com:formosa-crypto/formosa-keccak.git. Currently, we are using the AVX2 variant of the library.

Build instructions

To build the library and run functional tests, please execute the following commands (assuming the Jasmin compiler was previously built):

$ cd src/scloud_jasmin_ref
$ make tests

Repository structure

• src
  • scloud_python — executable specification in Python of the SCloud+ KEM
  • scloud_jasmin_ref — Jasmin implementation
  • scloud_cref — shared library build of the SCloud+ C implementation
• submodules
  • jasmin — development branch of the Jasmin compiler with floating-point support
  • formosa-keccack — third-party Jasmin implementation of SHA3
  • scloudplus — a fork of the the SCloud+ C implementation repository (https://github.com/scloudplus/scloudplus)
• env — support files (Dockerfile to build an environment with all required dependencies; etc.)

Building instructions:

Build the assembly files

Run the following commands (requires docker installed on your machine; in case of doubt, run docker run hello-world to check that everything is working):

$ docker pull tfaoliveira/jc
$ docker run --name jasmincode -it tfaoliveira/jc bash

$ git clone https://github.com/haslab/JasminCode.git

$ cd JasminCode/
$ git submodule init
$ git submodule update

$ cd src/scloud_jasmin_ref/
$ JASMINC=jasminc make
$ cd ../../../
$ exit # optional as you may want to explore the contents of the repository

Inside the docker container (that is now in Exited status as you may observe by running docker ps -a), in directory /workspace/JasminCode/src/scloud_jasmin_ref there are 3 assembly files that correspond to the result of compiling the Jasmin implementations into assembly using the Jasmin compiler:

• jscloud128.s
• jscloud192.s
• jscloud256.s

To copy them to the host machine, run, on the host machine, the following command:

$ docker cp jasmincode:/workspace/JasminCode/src/scloud_jasmin_ref/jscloud128.s .
$ docker cp jasmincode:/workspace/JasminCode/src/scloud_jasmin_ref/jscloud192.s .
$ docker cp jasmincode:/workspace/JasminCode/src/scloud_jasmin_ref/jscloud256.s .

Run the tests

This step assumes that you have run exit in the previous section and that the jasmincode container is in Exited status.

To run the tests run:

$ docker start jasmincode 
$ docker exec -it jasmincode bash
$ cd JasminCode/src/scloud_cref
$ make
$ cd ../../../
$ cd JasminCode/src/scloud_python/
$ make

Stop and remove the container

To stop and remove the container run the following commands:

$ docker stop jasmincode
$ docker rm jasmincode

To remove the docker image run the following command:

$ docker image rm tfaoliveira/jc