BLS threshold signature

An implementation of BLS threshold signature

Support architectures

• Windows Visual Studio / MSYS2(MinGW-w64)
• Linux
• macOS
• Android
• iOS
• WebAssembly

Support languages

• Go
• C#

Installation Requirements

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

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

News

• rename blsGetGeneratorOfG{1 or 2} to blsGetGeneratorOfPublicKey

• add blsSetETHserialization(1) to use ETH serialization for BLS12-381

• Support swap of G1 and G2 for Go (-tags bn384_256_swapg)

• blsInit() is not thread safe (pthread is not used)

• -tags option for Go bindings is always necessary

  • use -tags bn384_256 for BLS12-381

• support Android

• (Break backward compatibility) The suffix _dy of library name is removed and bls*.a requires libmcl.so set LD_LIBRARY_PATH to the directory.

• -tags option for Go bindings

  • -tags bn256
  • -tags bn384_256
  • -tags bn384

• Support swap of G1 and G2

  • make BLS_SWAP_G=1 then G1 is assigned to PublicKey and G2 is assigned to Signature.

• Build option without GMP

  • make MCL_USE_GMP=0

• Build option without OpenSSL

  • make MCL_USE_OPENSSL=0

• Build option to specify mcl directory

  • make MCL_DIR=<mcl directory>

• (old) libbls.a for C++ interface(bls/bls.hpp) is removed Link lib/libbls256.a or lib/libbls384.a to use bls/bls.hpp according to MCLBN_FP_UNIT_SIZE = 4 or 6.

Build and test for Linux

To make and test, run

cd bls
make test

To make sample programs, run

make sample_test

Build and test for Windows

1. make static library and use it

mklib
mk -s test\bls_c384_test.cpp
bin\bls_c384_test.exe

2. make dynamic library and use it

mklib dll
mk -d test\bls_c384_test.cpp
bin\bls_c384_test.exe

Build for Android

see readme.md

Build for iOS

cd bls
make gomobile

Library

• libbls256.a/libbls256.so ; for BN254 compiled with MCLBN_FP_UNIT_SIZE=4
• libbls384.a/libbls384.so ; for BN254/BN381_1/BLS12_381 compiled with MCLBN_FP_UNIT_SIZE=6
• libbls384_256.a/libbls384_256.so ; for BN254/BLS12_381 compiled with MCLBN_FP_UNIT_SIZE=6 and MCLBN_FR_UNIT_SIZE=4

See mcl/include/curve_type.h for curve parameter

Remark for static library

If there are both a shared library both and static library having the same name in the same directory, then the shared library is linked. So if you want to link a static library, then remove the shared library in the directory.

API

Basic API

BLS signature

e : G2 x G1 -> Fp12 ; optimal ate pairing over BN curve
Q in G2 ; fixed global parameter
H : {str} -> G1
s in Fr: secret key
sQ in G2; public key
s H(m) in G1; signature of m
verify ; e(sQ, H(m)) = e(Q, s H(m))

C

blsInit(MCL_BLS12_381, MCLBN_COMPILED_TIME_VAR); // use BLS12-381
blsSignatureVerifyOrder(0); // disable to check the order of a point in deserializing
blsPublicKeyVerifyOrder(0);
blsSetETHserialization(1); // obey ETH serialization

C++

void bls::init();

Initialize this library. Call this once to use the other api.

void SecretKey::init();

Initialize the instance of SecretKey. s is a random number.

void SecretKey::getPublicKey(PublicKey& pub) const;

Get public key sQ for the secret key s.

void SecretKey::sign(Sign& sign, const std::string& m) const;

Make sign s H(m) from message m.

bool Sign::verify(const PublicKey& pub, const std::string& m) const;

Verify sign with pub and m and return true if it is valid.

e(sQ, H(m)) == e(Q, s H(m))

Secret Sharing API

void SecretKey::getMasterSecretKey(SecretKeyVec& msk, size_t k) const;

Prepare k-out-of-n secret sharing for the secret key. msk[0] is the original secret key s and msk[i] for i > 0 are random secret key.

void SecretKey::set(const SecretKeyVec& msk, const Id& id);

Make secret key f(id) from msk and id where f(x) = msk[0] + msk[1] x + ... + msk[k-1] x^{k-1}.

You can make a public key f(id)Q from each secret key f(id) for id != 0 and sign a message.

void Sign::recover(const SignVec& signVec, const IdVec& idVec);

Collect k pair of sign f(id) H(m) and id for a message m and recover the original signature s H(m) for the secret key s.

PoP (Proof of Possesion)

void SecretKey::getPop(Sign& pop) const;

Sign pub and make a pop s H(sQ)

bool Sign::verify(const PublicKey& pub) const;

Verify a public key by pop.

Check the order of a point

deserializer functions check whether a point has correct order and the cost is heavy for especially G2. If you do not want to check it, then call

void blsSignatureVerifyOrder(false);
void blsPublicKeyVerifyOrder(false);

cf. subgroup attack

Go

make test_go

WASM(WebAssembly)

mkdir ../bls-wasm
make bls-wasm

• see bls-wasm
• see BLS signature demo on browser

License

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

Author

MITSUNARI Shigeo(herumi@nifty.com)