BLS threshold signature

This library is an implementation of BLS threshold signature, which supports the new BLS Signatures specified at Ethereum 2.0 Phase 0.

News

• 2023/Aug/17 The performance of Sign is improved.
• 2022/Apr/20 The performance of MulVec got 2x speed for n >= 256, but const attribute of some arguments of MulVec and MultiVerify is removed.
  • They may be normalized in processing but the value are not changed.
• 2021/Sep/16 update mcl and improve performance of isValidOrder, which is called from setStr/deserialize.
• 2021/Apr/28 add blsSetGeneratorOfPublicKey to change the generator.
• 2021/Jan/28 check zero public key on BLS_ETH mode
• 2020/Oct/07 add blsMultiVerify to process many verification all togather with multi thread.

Support architectures

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

Choice of groups

This library supports type-3 pairings such as BN curves and BLS curves. G1, G2, and GT are a cyclic group of prime order r.

e : G1 x G2 -> GT ; pairing

There are two ways for BLS signature.

type	SecretKey	PublicKey	Signature
default	Fr	G2	G1
ETH2.0 spec (BLS_ETH=1)	Fr	G1	G2

If you need ETH2.0 spec, then use this library with BLS_ETH=1 mode.

Interoperability of BLS signature on BLS12-381 pairing

If you want to use the same parameters as Ethereum 2.0, just define BLS_ETH. If you want to use mcl/bls without BLS_ETH, then check the following settings.

• Serialization/Deserialization between Fr/G1/G2 and byte sequences.
  • call blsSetETHserialization(1); to use the same specification as ETH2.0.
  • Serialize() compresses a point of G1/G2.
• The generator of G1/G2.
  • call blsPublicKeySetHexStr.
• Hash function from arbitrary byte sequences to G1/G2.
  • call blsSetMapToMode(MCL_MAP_TO_MODE_HASH_TO_CURVE); to use the same specification as ETH2.0.
  • call mclBnG1_setDst to set up domain separation.

For example, see initForDFINITY for DFINITY compatibility.

Support language bindings

language	ETH2.0 spec (PublicKey = G1)	default (PublicKey = G2)
Go	bls-eth-go-binary	bls-go-binary
WebAssembly (Node.js)	bls-eth-wasm	bls-wasm
Rust	bls-eth-rust	-

Compiled static library with BLS_ETH=1

The compiled static libraries with BLS_ETH=1 mode for {windows, darwin}/amd64, linux/{amd64, arm64} and android/{arm64-v8a, armeabi-v7a} are provided at bls-eth-go-binary/bls/lib.

Basic C API

Header files

#define BLS_ETH
#include <mcl/bn384_256.h>
#include <bls/bls.h>

Remark: BLS_ETH must always be defined before including bls/bls.h if you need ETH2.0 spec mode.

Initialization

// init library at once before calling the other APIs
int err = blsInit(MCL_BLS12_381, MCLBN_COMPILED_TIME_VAR);
if (err != 0) {
  printf("blsInit err %d\n", err);
  exit(1);
}

// use the latest eth2.0 spec
blsSetETHmode(BLS_ETH_MODE_LATEST);

Remark:

• blsInit and some functions which modify global settings such as blsSetETHmode are NOT thread-safe. The other functions are all thread-safe.
• blsSetETHmode is available for only BLS_ETH=1 mode.

KeyGen

Init a secret key sec and create a public key pub.

blsSecretKey sec;
blsPublicKey pub;

// init SecretKey sec by random number
blsSecretKeySetByCSPRNG(&sec);

// get PublicKey pub from SecretKey sec
blsGetPublicKey(&pub, &sec);

Sign

Make a signature sig of a message msg[0..msgSize-1] by the secret key sec.

blsSignature sig;
char msg[] = "hello";
const size_t msgSize = strlen(msg);

blsSign(&sig, &sec, msg, msgSize);

msg may contain \x00 if the correct msgSize is specified.

Verify

Verify the signature sig of the message msg[0..msgSize-1] by the public key pub.

// return 1 if it is valid else 0
int blsVerify(&sig, &pub, msg, msgSize);

Aggregate Signature

Aggregate Signatures sigVec[0], ..., sigVec[n-1] to aggSig. aggSig is cleared if n = 0.

void blsAggregateSignature(
  blsSignature *aggSig,
  const blsSignature *sigVec,
  mclSize n
);

FastAggregateVerify

Verify a signature sig of a message msg[0..msgSize-1] by pubVec[0], ..., pubVec[n-1].

int blsFastAggregateVerify(
  const blsSignature *sig,
  const blsPublicKey *pubVec,
  mclSize n,
  const void *msg,
  mclSize msgSize
);

AggregateVerify

• pubVec is n array of PublicKey
• msgVec is n * msgSize-byte array, which concatenates n-byte messages of length msgSize.

Verify Signature sig of (Message msgVec[msgSize * i..msgSize * (i+1)-1] and pubVec[i]) for i = 0, ..., n-1.

int blsAggregateVerifyNoCheck(
  const blsSignature *sig,
  const blsPublicKey *pubVec,
  const void *msgVec,
  mclSize msgSize,
  mclSize n
);

REMARK : blsAggregateVerifyNoCheck does not check

• sig has the correct order
• every n-byte messages of length msgSize are different from each other

Check them at the caller if necessary.

Functions corresponding to ETH2.0 spec names

bls.h	eth2.0 spec name
blsSign	Sign
blsVerify	Verify
blsAggregateSignature	Aggregate
blsFastAggregateVerify	FastAggregateVerify
blsAggregateVerifyNoCheck	AggregateVerify

Setter

int blsSecretKeySetLittleEndianMod(blsSecretKey *sec, const void *buf, mclSize bufSize);

Set sec to (buf[0..bufSize-1] as little endian) mod r and return 0 if bufSize <= 64 else -1.

Serialization

mclSize blsSecretKeySerialize(void *buf, mclSize maxBufSize, const blsSecretKey *sec);
mclSize blsPublicKeySerialize(void *buf, mclSize maxBufSize, const blsPublicKey *pub);
mclSize blsSignatureSerialize(void *buf, mclSize maxBufSize, const blsSignature *sig);

Serialize the instance to buf[0..maxBufSize-1] and return written byte size if success else 0.

mclSize blsSecretKeyDeserialize(blsSecretKey *sec, const void *buf, mclSize bufSize);
mclSize blsPublicKeyDeserialize(blsPublicKey *pub, const void *buf, mclSize bufSize);
mclSize blsSignatureDeserialize(blsSignature *sig, const void *buf, mclSize bufSize);

Deserialize buf[0..bufSize-1] to the instance and return read byte size if success else 0.

Check order

Check whether sig and pub have the correct order r.

// return 1 if it is valid else 0
int blsSignatureIsValidOrder(const blsSignature *sig);
int blsPublicKeyIsValidOrder(const blsPublicKey *pub);

API for k-of-n threshold signature

1. Prepare k secret keys (msk).
2. Make n secret keys from msk by blsSecretKeyShare.
3. Each user makes the public key from the given secret key.
4. Each user makes a signature for the same message.
5. Any k subset of n signatures can recover the master signature by blsSignatureRecover.

See sample/minsample.c for the details.

int blsSecretKeyShare(blsSecretKey *sec, const blsSecretKey *msk, mclSize k, const blsId *id);

Make sec corresponding to id from {msk[i] for i = 0, ..., k-1}.

int blsSignatureRecover(blsSignature *sig, const blsSignature *sigVec, const blsId *idVec, mclSize n);

Recover sig from {(sigVec[i], idVec[i]) for i = 0, ..., n-1}.

Multi aggregate signature (experimental)

blsMultiAggregateSignature and blsMultiAggregatePublicKey are provided for BLS Multi-Signatures With Public-Key Aggregation. The hash function is temporary. See blsMultiAggregateTest.

void blsMultiAggregateSignature(
  blsSignature *aggSig,
  blsSignature *sigVec,
  blsPublicKey *pubVec,
  mclSize n
);

Set aggSig = sum_{i=0^n-1} sigVec[i] t_i, where (t_1, ..., t_n) = Hash({pubVec[0..n-1]}).

void blsMultiAggregatePublicKey(
  blsPublicKey *aggPub,
  blsPublicKey *pubVec,
  mclSize n
);

Set aggPub = sum_{i=0^n-1} pubVec[i] t_i, where (t_1, ..., t_n) = Hash({pubVec[0..n-1]}).

How to build a static library by ownself

The following description is for BLS_ETH=1 mode. Remove it if you need PublicKey as G1.

Preliminaries

git clone --recursive https://github.com/herumi/bls

Build static library for Linux and macOS

make -C mcl lib/libmcl.a
make BLS_ETH=1 lib/libbls384_256.a

If the option MCL_USE_GMP=0 (resp.MCL_USE_OPENSSL=0) is used then GMP (resp. OpenSSL) is not used.

Build library for Windows

Open the x64 Native Tools for Visual Studio and type the following command.

static library

mklib eth

dynamic library

mklib dll eth

Or open bls.sln and build it. REMARK CmakeLists.txt is not maintained for Visual Studio.

Build static library for Android

See bls-eth-go-binary

History

• 2020/May/13 : blsSetETHmode() supports BLS_ETH_MODE_DRAFT_07 defined at BLS12381G2_XMD:SHA-256_SSWU_RO_.
• 2020/Apr/02 : experimental add blsMultiAggregateSignature/blsMultiAggregatePublicKey multiSig
  • The hash function is temporary, which may be modified in the future.
• 2020/Mar/26 : DST of hash-to-curve of mcl is changed, so the output has also changed for BLS_ETH_MODE_DRAFT_06.
• 2020/Mar/15 : blsSetETHmode() supports BLS_ETH_MODE_DRAFT_06 defined at draft-irtf-cfrg-hash-to-curve at March 2020. But it has not yet fully tested.

License

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

Author

MITSUNARI Shigeo([email protected])

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