Scarab

FHE Library for encrypting/decrypting bits and performing add/mul (and/xor) over encrypted data. Port/fork of the existing library by Henning Perl.

Dependencies

• GMP: The GNU Multiple Precision Arithmetic Library — https://gmplib.org/ (or MPIR in GMP mode)
• MPIR: The GNU Multiple Precision Integers and Rationals — http://mpir.org/ (or GMP)
• MPFR: The GNU Multiple Precision Floating-Point Reliably — http://www.mpfr.org/ (required by FLINT)
• FLINT: Fast Library for Number Theory — http://flintlib.org/ (version 2.4.1+)

Building

The compilation is done using GYP and make.

$ gyp --depth=.
$ make

See Dockerfile for build instructions.

Debian-based

apt-get -yy install libflint-2.5.2 libflint-dev libgmp-dev libmpfr-dev gcc g++ make automake autoconf gyp.

RHEL-based

yum install gcc gcc-c++ make automake autoconf mpfr-devel gmp-devel gyp.

Note:

• You will need epel-release to download gyp
• Flint must be compiled from sources

Windows

You can compile library under cygwin-x64 on Windows too. Just make sure you have installed all the following libs:

• gcc-core
• gcc-g++
• gmp
• mpfr
• autoconf2.1
• automake1.14
• libmprf4
• libmprf-devel
• libgmp10
• libgmpxx4
• libgmp-devel
• make

Usage

You can use the library as demonstrated in test.c.

#include "scarab.h"

Used types:

type	usage
fhe_pk_t pk;	Private key
fhe_sk_t sk;	Shared key
mpz_t c;	Encrypted message container

Used functions:

function prototype	meaning
void fhe_pk_init(fhe_pk_t pk);	Initialize private key
void fhe_pk_clear(fhe_pk_t pk);	Clear private key (destroy)
void fhe_sk_init(fhe_sk_t sk);	Initialize shared key
void fhe_sk_clear(fhe_sk_t sk);	Clear shared key (destroy)
void fhe_keygen(fhe_pk_t pk, fhe_sk_t sk);	Generate a keypair
void fhe_encrypt(mpz_t c, fhe_pk_t pk, int m);	Encrypt a message (0 or 1)
int fhe_decrypt(mpz_t c, fhe_sk_t sk);	Decrypt a cyphertext
void fhe_recrypt(mpz_t c, fhe_pk_t pk, fhe_sk_t sk);	Recrypt a cyphertext (“refreshing” it)
void fhe_add(mpz_t res, mpz_t a, mpz_t b, fhe_pk_t pk);	Add cyphertexts (= XOR)
void fhe_mul(mpz_t res, mpz_t a, mpz_t b, fhe_pk_t pk);	Multiply cyphertexts (= AND)
void fhe_fulladd(mpz_t sum, mpz_t c_out, mpz_t a, mpz_t b, mpz_t c_in, fhe_pk_t pk);	Add with carry in and carry out
void fhe_halfadd(mpz_t sum, mpz_t c_out, mpz_t a, mpz_t b, fhe_pk_t pk);	Add with carry out

References

1. C. Gentry, A fully homomorphic encryption scheme
2. N. Smart and F. Vercauteren, Fully Homomorphic Encryption with Relatively Small Key and Ciphertext Sizes
3. H. Perl, M. Brenner and M. Smith, POSTER: An Implementation of the Fully Homomorphic Smart-Vercauteren Crypto-System