mcl

A portable and fast pairing-based cryptography library.

Abstract

mcl is a library for pairing-based cryptography. The current version supports the optimal Ate pairing over BN curves and BLS12-381 curves.

News

• (Break backward compatibility) libmcl_dy.a is renamed to libmcl.a
  • The option SHARE_BASENAME_SUF is removed
• 2nd argument of mclBn_init is changed from maxUnitSize to compiledTimeVar, which must be MCLBN_COMPILED_TIME_VAR.
• break backward compatibility of mapToGi for BLS12. A map-to-function for BN is used. If MCL_USE_OLD_MAPTO_FOR_BLS12 is defined, then the old function is used, but this will be removed in the future.

Support architecture

• x86-64 Windows + Visual Studio
• x86, x86-64 Linux + gcc/clang
• ARM Linux
• ARM64 Linux
• (maybe any platform to be supported by LLVM)
• WebAssembly

Support curves

p(z) = 36z^4 + 36z^3 + 24z^2 + 6z + 1.

• BN254 ; a BN curve over the 254-bit prime p(z) where z = -(2^62 + 2^55 + 1).
• BN_SNARK1 ; a BN curve over a 254-bit prime p such that n := p + 1 - t has high 2-adicity.
• BN381_1 ; a BN curve over the 381-bit prime p(z) where z = -(2^94 + 2^76 + 2^72 + 1).
• BN462 ; a BN curve over the 462-bit prime p(z) where z = 2^114 + 2^101 - 2^14 - 1.
• BLS12_381 ; a BLS12-381 curve

Benchmark

The latest benchmark(2018/11/7)

Intel Core i7-6700 3.4GHz(Skylake), Ubuntu 18.04.1 LTS

curveType	binary	clang-6.0.0	gcc-7.3.0
BN254	bin/bn_test.exe	882Kclk	933Kclk
BLS12-381	bin/bls12_test.exe	2290Kclk	2630Kclk

Intel Core i7-7700 3.6GHz(Kaby Lake), Ubuntu 18.04.1 LTS on Windows 10 Vmware

curveType	binary	clang-6.0.0	gcc-7.3.0
BN254	bin/bn_test.exe	900Kclk	954Kclk
BLS12-381	bin/bls12_test.exe	2340Kclk	2680Kclk

• now investigating the reason why gcc is slower than clang.

Higher-bit BN curve benchmark

For JavaScript(WebAssembly), see ID based encryption demo.

paramter	x64	Firefox on x64	Safari on iPhone7
BN254	0.25	2.48	4.78
BN381_1	0.95	7.91	11.74
BN462	2.16	14.73	22.77

• x64 : 'Kaby Lake Core i7-7700(3.6GHz)'.
• Firefox : 64-bit version 58.
• iPhone7 : iOS 11.2.1.
• BN254 is by test/bn_test.cpp.
• BN381_1 and BN462 are by test/bn512_test.cpp.
• All the timings are given in ms(milliseconds).

The other benchmark results are bench.txt.

An old benchmark of a BN curve BN254(2016/12/25).

• x64, x86 ; Inte Core i7-6700 3.4GHz(Skylake) upto 4GHz on Ubuntu 16.04.
  • sudo cpufreq-set -g performance
• arm ; 900MHz quad-core ARM Cortex-A7 on Raspberry Pi2, Linux 4.4.11-v7+
• arm64 ; 1.2GHz ARM Cortex-A53 HiKey

software	x64	x86	arm	arm64(msec)
ate-pairing	0.21	-	-	-
mcl	0.31	1.6	22.6	3.9
TEPLA	1.76	3.7	37	17.9
RELIC PRIME=254	0.30	3.5	36	-
MIRACL ake12bnx	4.2	-	78	-
NEONabe	-	-	16	-

• compile option for RELIC

cmake -DARITH=x64-asm-254 -DFP_PRIME=254 -DFPX_METHD="INTEG;INTEG;LAZYR" -DPP_METHD="LAZYR;OATEP"

Installation Requirements

• GMP and OpenSSL

apt install libgmp-dev libssl-dev

Create a working directory (e.g., work) and clone the following repositories.

mkdir work
cd work
git clone git://github.com/herumi/mcl
git clone git://github.com/herumi/cybozulib_ext ; for only Windows

• Cybozulib_ext is a prerequisite for running OpenSSL and GMP on VC (Visual C++).

(Option) Without GMP

make MCL_USE_GMP=0

Define MCL_USE_VINT before including bn.hpp

(Option) Without Openssl

make MCL_USE_OPENSSL=0

Define MCL_DONT_USE_OPENSSL before including bn.hpp

Build and test on x86-64 Linux, macOS, ARM and ARM64 Linux

To make lib/libmcl.a and test it:

cd work/mcl
make test

To benchmark a pairing:

bin/bn_test.exe

To make sample programs:

make sample

if you want to change compiler options for optimization, then set CFLAGS_OPT_USER.

make CLFAGS_OPT_USER="-O2"

Build for 32-bit Linux

Build openssl and gmp for 32-bit mode and install <lib32>

make ARCH=x86 CFLAGS_USER="-I <lib32>/include" LDFLAGS_USER="-L <lib32>/lib -Wl,-rpath,<lib32>/lib"

Build for 64-bit Windows

1. make static library and use it

mklib
mk -s test\bn_c256_test.cpp
bin\bn_c256_test.exe

2. make dynamic library and use it

mklib dll
mk -d test\bn_c256_test.cpp
bin\bn_c256_test.exe

open mcl.sln and build or if you have msbuild.exe

msbuild /p:Configuration=Release

Build with cmake

For Linux,

mkdir build
cd build
cmake ..
make

For Visual Studio,

mkdir build
cd build
cmake .. -A x64
msbuild mcl.sln /p:Configuration=Release /m

Build for wasm(WebAssembly)

mcl supports emcc (Emscripten) and test/bn_test.cpp runs on browers such as Firefox, Chrome and Edge.

• IBE on browser
• SHE on browser
• BLS signature on brower

The timing of a pairing on BN254 is 2.8msec on 64-bit Firefox with Skylake 3.4GHz.

Node.js

• mcl-wasm pairing library
• bls-wasm BLS signature library
• she-wasm 2 Level Homomorphic Encryption library

SELinux

mcl uses Xbyak JIT engine if it is available on x64 architecture, otherwise mcl uses a little slower functions generated by LLVM. The default mode enables SELinux security policy on CentOS, then JIT is disabled.

% sudo setenforce 1
% getenforce
Enforcing
% bin/bn_test.exe
JIT 0
pairing   1.496Mclk
finalExp 581.081Kclk

% sudo setenforce 0
% getenforce
Permissive
% bin/bn_test.exe
JIT 1
pairing   1.394Mclk
finalExp 546.259Kclk

Libraries

• G1 and G2 is defined over Fp
• The order of G1 and G2 is r.
• Use bn256.hpp if only BN254 is used.

C++ library

• libmcl.a ; static C++ library of mcl
• libmcl.so ; shared C++ library of mcl
• the default parameter of curveType is BN254

header	support curveType	sizeof Fr	sizeof Fp
bn256.hpp	BN254	32	32
bls12_381.hpp	BLS12_381, BN254	32	48
bn384.hpp	BN381_1, BLS12_381, BN254	48	48

C library

• Define MCLBN_FR_UNIT_SIZE and MCLBN_FP_UNIT_SIZE and include bn.h
• set MCLBN_FR_UNIT_SIZE = MCLBN_FP_UNIT_SIZE unless MCLBN_FR_UNIT_SIZE is defined

library	MCLBN_FR_UNIT_SIZE	MCLBN_FP_UNIT_SIZE
sizeof	Fr	Fp
libmclbn256.a	4	4
libmclbn384_256.a	4	6
libmclbn384.a	6	6

• libmclbn*.a ; static C library
• libmclbn*.so ; shared C library

2nd argument of mclBn_init

Specify MCLBN_COMPILED_TIME_VAR to 2nd argument of mclBn_init, which is defined as MCLBN_FR_UNIT_SIZE * 10 + MCLBN_FP_UNIT_SIZE. This parameter is used to make sure that the values are the same when the library is built and used.

How to initialize pairing library

Call mcl::bn256::initPairing before calling any operations.

#include <mcl/bn256.hpp>
mcl::bn::CurveParam cp = mcl::BN254; // or mcl::BN_SNARK1
mcl::bn256::initPairing(cp);
mcl::bn256::G1 P(...);
mcl::bn256::G2 Q(...);
mcl::bn256::Fp12 e;
mcl::bn256::pairing(e, P, Q);

1. (BN254) a BN curve over the 254-bit prime p = p(z) where z = -(2^62 + 2^55 + 1).
2. (BN_SNARK1) a BN curve over a 254-bit prime p such that n := p + 1 - t has high 2-adicity.
3. BN381_1 with mcl/bn384.hpp.
4. BN462 with mcl/bn512.hpp.

See test/bn_test.cpp.

Default constructor of Fp, Ec, etc.

A default constructor does not initialize the instance. Set a valid value before reffering it.

Definition of groups

The curve equation for a BN curve is:

E/Fp: y^2 = x^3 + b .

• the cyclic group G1 is instantiated as E(Fp)[n] where n := p + 1 - t;
• the cyclic group G2 is instantiated as the inverse image of E'(Fp^2)[n] under a twisting isomorphism phi from E' to E; and
• the pairing e: G1 x G2 -> Fp12 is the optimal ate pairing.

The field Fp12 is constructed via the following tower:

• Fp2 = Fp[u] / (u^2 + 1)
• Fp6 = Fp2[v] / (v^3 - Xi) where Xi = u + 1
• Fp12 = Fp6[w] / (w^2 - v)
• GT = { x in Fp12 | x^r = 1 }

Arithmetic operations

G1 and G2 is additive group and has the following operations:

• T::add(T& z, const T& x, const T& y); // z = x + y
• T::sub(T& z, const T& x, const T& y); // z = x - y
• T::neg(T& y, const T& x); // y = -x
• T::mul(T& z, const T& x, const INT& y); // z = y times scalar multiplication of x

Remark: &z == &x or &y are allowed. INT means integer type such as Fr, int and mpz_class.

T::mul uses GLV method then G2::mul returns wrong value if x is not in G2. Use T::mulGeneric(T& z, const T& x, const INT& y) for x in phi^-1(E'(Fp^2)) - G2.

Fp, Fp2, Fp6 and Fp12 have the following operations:

• T::add(T& z, const T& x, const T& y); // z = x + y
• T::sub(T& z, const T& x, const T& y); // z = x - y
• T::mul(T& z, const T& x, const T& y); // z = x * y
• T::div(T& z, const T& x, const T& y); // z = x / y
• T::neg(T& y, const T& x); // y = -x
• T::inv(T& y, const T& x); // y = 1/x
• T::pow(T& z, const T& x, const INT& y); // z = x^y
• Fp12::unitaryInv(T& y, const T& x); // y = conjugate of x

Remark: Fp12::mul uses GLV method then returns wrong value if x is not in GT. Use Fp12::mulGeneric for x in Fp12 - GT.

Map To points

Use these functions to make a point of G1 and G2.

• mapToG1(G1& P, const Fp& x); // assume x != 0
• mapToG2(G2& P, const Fp2& x);
• hashAndMapToG1(G1& P, const void *buf, size_t bufSize); // set P by the hash value of [buf, bufSize)
• hashAndMapToG2(G2& P, const void *buf, size_t bufSize);

These functions maps x into Gi according to [[Faster hashing to G2]].

String format of G1 and G2

G1 and G2 have three elements of Fp (x, y, z) for Jacobi coordinate. normalize() method normalizes it to affine coordinate (x, y, 1) or (0, 0, 0).

getStr() method gets

• 0 ; infinity
• 1 <x> <y> ; not compressed format
• 2 <x> ; compressed format for even y
• 3 <x> ; compressed format for odd y

Generator of G1 and G2

If you want to use the same generators of BLS12-381 with zkcrypto then,

// G1 P
P.setStr('1 3685416753713387016781088315183077757961620795782546409894578378688607592378376318836054947676345821548104185464507 1339506544944476473020471379941921221584933875938349620426543736416511423956333506472724655353366534992391756441569')

// G2 Q
Q.setStr('1 352701069587466618187139116011060144890029952792775240219908644239793785735715026873347600343865175952761926303160 3059144344244213709971259814753781636986470325476647558659373206291635324768958432433509563104347017837885763365758 1985150602287291935568054521177171638300868978215655730859378665066344726373823718423869104263333984641494340347905 927553665492332455747201965776037880757740193453592970025027978793976877002675564980949289727957565575433344219582')

Serialization format of G1 and G2

pseudo-code to serialize of p

if bit-length(p) % 8 != 0:
  size = Fp::getByteSize()
  if p is zero:
    return [0] * size
  else:
    s = x.serialize()
    # x in Fp2 is odd <=> x.a is odd
    if y is odd:
      s[byte-length(s) - 1] |= 0x80
    return s
else:
  size = Fp::getByteSize() + 1
  if p is zero:
    return [0] * size
  else:
    s = x.serialize()
    if y is odd:
      return 2:s
    else:
      return 3:s

Verify an element in G2

G2::isValid() checks that the element is in the curve of G2 and the order of it is r for subgroup attack. G2::set(), G2::setStr and operator<< also check the order. If you check it out of the library, then you can stop the verification by calling G2::verifyOrderG2(false).

How to make asm files (optional)

The asm files generated by this way are already put in src/asm, then it is not necessary to do this.

Install LLVM.

make MCL_USE_LLVM=1 LLVM_VER=<llvm-version> UPDATE_ASM=1

For example, specify -3.8 for <llvm-version> if opt-3.8 and llc-3.8 are installed.

If you want to use Fp with 1024-bit prime on x86-64, then

make MCL_USE_LLVM=1 LLVM_VER=<llvm-version> UPDATE_ASM=1 MCL_MAX_BIT_SIZE=1024

API for Two level homomorphic encryption

• Efficient Two-level Homomorphic Encryption in Prime-order Bilinear Groups and A Fast Implementation in WebAssembly, N. Attrapadung, G. Hanaoka, S. Mitsunari, Y. Sakai, K. Shimizu, and T. Teruya. ASIACCS 2018
• she-api
• she-api(Japanese)

Java API

See java.md

License

modified new BSD License http://opensource.org/licenses/BSD-3-Clause

This library contains some part of the followings software licensed by BSD-3-Clause.

• xbyak
• cybozulib
• Lifted-ElGamal

References

• ate-pairing
• Faster Explicit Formulas for Computing Pairings over Ordinary Curves, D.F. Aranha, K. Karabina, P. Longa, C.H. Gebotys, J. Lopez, EUROCRYPTO 2011, (preprint)
• High-Speed Software Implementation of the Optimal Ate Pairing over Barreto-Naehrig Curves, Jean-Luc Beuchat, Jorge Enrique González Díaz, Shigeo Mitsunari, Eiji Okamoto, Francisco Rodríguez-Henríquez, Tadanori Teruya, Pairing 2010, (preprint)
• Faster hashing to G2,Laura Fuentes-Castañeda, Edward Knapp, Francisco Rodríguez-Henríquez, SAC 2011, (preprint)
• Skew Frobenius Map and Efficient Scalar Multiplication for Pairing–Based Cryptography, Y. Sakemi, Y. Nogami, K. Okeya, Y. Morikawa, CANS 2008.

History

• 2019/Mar/22 v0.92 shortcut for Ec::mul(Px, P, x) if P = 0
• 2019/Mar/21 python binding of she256 for Linux/Mac/Windows
• 2019/Mar/14 v0.91 modp supports mcl-wasm
• 2019/Mar/12 v0.90 fix Vint::setArray(x) for x == this
• 2019/Mar/07 add mclBnFr_setLittleEndianMod, mclBnFp_setLittleEndianMod
• 2019/Feb/20 LagrangeInterpolation sets out = yVec[0] if k = 1
• 2019/Jan/31 add mclBnFp_mapToG1, mclBnFp2_mapToG2
• 2019/Jan/31 fix crash on x64-CPU without AVX (thanks to mortdeus)

Author

光成滋生 MITSUNARI Shigeo(herumi@nifty.com)