Overview

Fully Homomorphic Encryption (FHE) is a technique that makes it possible to perform computations on encrypted data without the need to decrypt it first. While this technique is promising, multiple obstacles have prevented its widespread adoption, including its complexity and slowness. Compilers were developed to simplify the process for non-FHE expert developers by offering a user-friendly frontend to write their programs and optimize them for the best runtime.

CHEHAB is an FHE compiler that offers a simple Domain Specific Language (DSL) to define inputs and outputs and describe the desired computations. CHEHAB abstracts FHE complexities by automating the selection of optimal parameters that can support the generated noise and inserting ciphertext maintenance operations. It also supports multiple optimization techniques like Constant Folding (CF), Common Sub-expression Elimination (CSE), and Term Rewriting System (TRS) as the main optimization technique. Currently, CHEHAB supports only the BFV scheme and targets the SEAL library.

Example

Here is an example written in our compiler's DSL

#include "fheco/fheco.hpp"
using namespace fheco;
void example()
{
  Ciphertext c0("c0");
  Ciphertext c1 = c0 << 1;
  Ciphertext c2 = c0 << 5;
  Ciphertext c3 = c0 << 6;
  Ciphertext c4 = c1 + c0;
  Ciphertext c5 = c2 + c3;
  Ciphertext c6 = c4 + c5;
  c6.set_output("c6");
}

Building CHEHAB

In order to build and use the compiler, you need to have installed:

• Cmake
• GCC compiler
• SEAL library

To build CHEHAB, you need to follow these steps:

1. Clone the repository to your local machine.

git clone https://github.com/Modern-Compilers-Lab/CHEHAB.git

2. Navigate to the cloned repository.

cd CHEHAB

3. Create a directory to build the compiler in

mkdir build
cmake -S . -B build

4. Build the compiler

cd build
make

Running the benchmarks

Benchmark codes can be found in the benchmarks directory in the repository's main directory, while their executables can be found in the benchmarks directory within the build directory.

A benchmark is run in two phases. The first execution triggers our compiler to translate the program written in our DSL into a program using FHE native primitives. The second execution corresponds to the concrete homomorphic evaluation. In the following steps, we use the box blur benchmark as an example.

1. While in the build directory, navigate to the corresponding benchmark directory and run its executable.

cd benchmarks/box_blur
./box_blur

2. Navigate to the he directory, where you can find the created files to build the final executable. This automatically links the generated file with the SEAL library.

cd he
mkdir build
cmake -S . -B build
cd build
make

3. Within the build directory, you will find the main executable that triggers the concrete homomorphic evaluation. You only need to execute the main file.

./main

This will use the box_blur_io_example.txt file, included in the build directory to extract the input values, encode them, and then encrypt them for use in the homomorphic evaluation.