High-level API in C

This document describes the C bindings to the TFHE-rs high-level primitives for creating Fully Homomorphic Encryption (FHE) programs.

Setting up TFHE-rs C API for C programming.

You can build TFHE-rs C API using the following command:

RUSTFLAGS="-C target-cpu=native" cargo +nightly build --release --features=high-level-c-api -p tfhe

Locate files in the right path:

• In ${REPO\_ROOT}/target/release/, you can find:

  • The tfhe.h header

  • The static (.a) and dynamic (.so) libtfhe binaries

• In ${REPO\_ROOT}/target/release/deps/, you can find:

  • The tfhe-c-api-dynamic-buffer.h header

  • The static (.a) and dynamic (.so) libraries

Ensure your build system configures the C or C++ program links against TFHE-rs C API binaries and the dynamic buffer library.

The following is a minimal CMakeLists.txt configuration example:

project(my-project)

cmake_minimum_required(VERSION 3.16)

set(TFHE_C_API "/path/to/tfhe-rs/target/release")

include_directories(${TFHE_C_API})
include_directories(${TFHE_C_API}/deps)
add_library(tfhe STATIC IMPORTED)
set_target_properties(tfhe PROPERTIES IMPORTED_LOCATION ${TFHE_C_API}/libtfhe.a)

if(APPLE)
    find_library(SECURITY_FRAMEWORK Security)
    if (NOT SECURITY_FRAMEWORK)
        message(FATAL_ERROR "Security framework not found")
    endif()
endif()

set(EXECUTABLE_NAME my-executable)
add_executable(${EXECUTABLE_NAME} main.c)
target_include_directories(${EXECUTABLE_NAME} PRIVATE ${CMAKE_CURRENT_SOURCE_DIR})
target_link_libraries(${EXECUTABLE_NAME} LINK_PUBLIC tfhe m pthread dl)
if(APPLE)
    target_link_libraries(${EXECUTABLE_NAME} LINK_PUBLIC ${SECURITY_FRAMEWORK})
endif()
target_compile_options(${EXECUTABLE_NAME} PRIVATE -Werror)

Commented code of a uint128 subtraction using TFHE-rs C API.

The following example demonstrates uint128 subtraction using the TFHE-rs C API:

WARNING: this example omits proper memory management in the error case to improve code readability.

Ensure the above CMakeLists.txt and main.c files are in the same directory. Use the following commands to execute the example:

# /!\ Be sure to update CMakeLists.txt to give the absolute path to the compiled tfhe library
$ ls
CMakeLists.txt  main.c
$ mkdir build && cd build
$ cmake .. -DCMAKE_BUILD_TYPE=RELEASE
...
$ make
...
$ ./my-executable
FHE computation successful!
$

#include "tfhe.h"
#include <assert.h>
#include <stdio.h>

int main(void)
{
    int ok = 0;
    // Prepare the config builder for the high level API and choose which types to enable
    ConfigBuilder *builder;
    Config *config;

    // Put the builder in a default state without any types enabled
    config_builder_default(&builder);
    // Populate the config
    config_builder_build(builder, &config);

    ClientKey *client_key = NULL;
    ServerKey *server_key = NULL;

    // Generate the keys using the config
    generate_keys(config, &client_key, &server_key);
    // Set the server key for the current thread
    set_server_key(server_key);

    FheUint128 *lhs = NULL;
    FheUint128 *rhs = NULL;
    FheUint128 *result = NULL;
    // A 128-bit unsigned integer containing value: 20 << 64 | 10
    U128 clear_lhs = { .w0 = 10, .w1 = 20 };
    // A 128-bit unsigned integer containing value: 2 << 64 | 1
    U128 clear_rhs = { .w0 = 1, .w1 = 2 };

    ok = fhe_uint128_try_encrypt_with_client_key_u128(clear_lhs, client_key, &lhs);
    assert(ok == 0);

    ok = fhe_uint128_try_encrypt_with_client_key_u128(clear_rhs, client_key, &rhs);
    assert(ok == 0);

    // Compute the subtraction
    ok = fhe_uint128_sub(lhs, rhs, &result);
    assert(ok == 0);

    U128 clear_result;
    // Decrypt
    ok = fhe_uint128_decrypt(result, client_key, &clear_result);
    assert(ok == 0);

    // Here the subtraction allows us to compare each word
    assert(clear_result.w0 == 9);
    assert(clear_result.w1 == 18);

    // Destroy the ciphertexts
    fhe_uint128_destroy(lhs);
    fhe_uint128_destroy(rhs);
    fhe_uint128_destroy(result);

    // Destroy the keys
    client_key_destroy(client_key);
    server_key_destroy(server_key);

    printf("FHE computation successful!\n");
    return EXIT_SUCCESS;
}