Multi-party ECDSA

This project is a Rust implementation of {t,n}-threshold ECDSA (elliptic curve digital signature algorithm).

Threshold ECDSA includes two protocols:

• Key Generation for creating secret shares.
• Signing for using the secret shares to generate a signature.

ECDSA is used extensively for crypto-currencies such as Bitcoin, Ethereum (secp256k1 curve), NEO (NIST P-256 curve) and much more. This library can be used to create MultiSig and ThresholdSig crypto wallet. For a full background on threshold signatures please read our Binance academy article Threshold Signatures Explained.

Library Introduction

The library was built with four core design principles in mind:

1. Multi-protocol support
2. Built for cryptography engineers
3. Foolproof
4. Black box use of cryptographic primitives

To learn about the core principles as well as on the audit process and security of the library, please read our Intro to multiparty ecdsa library blog post.

Use It

The library implements four different protocols for threshold ECDSA. The protocols presents different tradeoffs in terms of parameters, security assumptions and efficiency.

Protocol	High Level code
Lindell 17 [1]	Gotham-city (accepted to CIW19) is a two party bitcoin wallet, including benchmarks. KMS is a Rust wrapper library that implements a general purpose two party key management system. thresh-sig-js is a Javascript SDK
Gennaro, Goldfeder 19 [2] (video)	tss-ecdsa-cli is a wrapper CLI for full threshold access structure, including network and threshold HD keys (BIP32). See Demo in this library to get better low level understanding
Castagnos et. al. 19 [3]	Currently enabled as a feature in this library. To Enable, build with --features=cclst. to Test, use cargo test --features=cclst -- --test-threads=1
Gennaro, Goldfeder 20 [4]	A full threshold protocol that supports identifying malicious parties. If signing fails - a list of malicious parties is returned. The protocol requires only a broadcast channel (all messages are broadcasted)

Run GG20 Demo

In the following steps we will generate 2-of-3 threshold signing key and sign a message with 2 parties.

Setup

1. You need Rust and GMP library (optionally) to be installed on your computer.

2. • Run cargo build --release --examples
   • Don't have GMP installed? Use this command instead:

     cargo build --release --examples --no-default-features --features curv-kzen/num-bigint

     But keep in mind that it will be less efficient.

   Either of commands will produce binaries into ./target/release/examples/ folder.

3. cd ./target/release/examples/

Start an SM server

./gg20_sm_manager

That will start an HTTP server on http://127.0.0.1:8000. Other parties will use that server in order to communicate with each other. Note that communication channels are neither encrypted nor authenticated. In production, you must encrypt and authenticate parties messages.

Run Keygen

Open 3 terminal tabs for each party. Run:

1. ./gg20_keygen -t 1 -n 3 -i 1 --output local-share1.json
2. ./gg20_keygen -t 1 -n 3 -i 2 --output local-share2.json
3. ./gg20_keygen -t 1 -n 3 -i 3 --output local-share3.json

Each command corresponds to one party. Once keygen is completed, you'll have 3 new files: local-share1.json, local-share2.json, local-share3.json corresponding to local secret share of each party.

Run Signing

Since we use 2-of-3 scheme (t=1 n=3), any two parties can sign a message. Run:

1. ./gg20_signing -p 1,2 -d "hello" -l local-share1.json
2. ./gg20_signing -p 1,2 -d "hello" -l local-share2.json

Each party will produce a resulting signature. -p 1,2 specifies indexes of parties who attends in signing (each party has an associated index given at keygen, see argument -i), -l file.json sets a path to a file with secret local share, and -d "hello" is a message being signed.

Running Demo on different computers

While previous steps show how to run keygen & signing on local computer, you actually can run each party on dedicated machine. To do this, you should ensure that parties can reach SM Server, and specify its address via command line argument, eg:

./gg20_keygen --address http://10.0.1.9:8000/ ...

Run GG18 Demo

The following steps are for setup, key generation with n parties and signing with t+1 parties.

Setup

1. We use shared state machine architecture (see white city). The parameters parties and threshold can be configured by changing the file: param. a keygen will run with parties parties and signing will run with any subset of threshold + 1 parties. param file should be located in the same path of the client software.

2. Install Rust. Run cargo build --release --examples (it will build into /target/release/examples/)

3. Run the shared state machine: ./gg18_sm_manager. By default, it's configured to be in 127.0.0.1:8000, this can be changed in Rocket.toml file. The Rocket.toml file should be in the same folder you run sm_manager from.

KeyGen

run gg18_keygen_client as follows: ./gg18_keygen_client http://127.0.0.1:8000 keys.store. Replace IP and port with the ones configured in setup. Once n parties join the application will run till finish. At the end each party will get a local keys file keys.store (change filename in command line). This contains secret and public data of the party after keygen. The file therefore should remain private.

Sign

Run ./gg18_sign_client. The application should be in the same folder as the keys.store file (or custom filename generated in keygen). the application takes three arguments: IP:port as in keygen, filename and message to be signed: ./gg18_sign_client http://127.0.0.1:8001 keys.store "KZen Networks". The same message should be used by all signers. Once t+1 parties join the protocol will run and will output to screen signature (R,s).

The ./gg18_sign_client executable initially tries to unhex its input message (the third parameter). Before running ensure two things:

1. If you want to pass a binary message to be signed - hex it.
2. If you want to pass a textual message in a non-hex form, make sure it can't be unhexed. Simply put, the safest way to use the signing binary is to just always hex your messages before passing them to the ./gg18_sign_client executable.

Example

To sign the message hello world, first calculate its hexadecimal representation. This yields the 68656c6c6f20776f726c64. Then, run:

./gg18_sign_client http://127.0.0.1:8000 keys.store "68656c6c6f20776f726c64"

GG18 demo

Run ./run.sh (located in /demo folder) in the main folder. Move params file to the same folder as the executables (usually /target/release/examples). The script will spawn a shared state machine, clients in the number of parties and signing requests for the threshold + 1 first parties.

gg18_sm_manager rocket server runs in production mode by default. You may modify the ./run.sh to config it to run in different environments. For example, to run rocket server in development:

ROCKET_ENV=development ./target/release/examples/sm_manager

Contributions & Development Process

The contribution workflow is described in CONTRIBUTING.md, in addition the Rust utilities wiki contains information on workflow and environment set-up.

License

Multi-party ECDSA is released under the terms of the GPL-3.0 license. See LICENSE for more information.

Contact

Feel free to reach out or join ZenGo X Telegram for discussions on code and research.

References

[1] https://eprint.iacr.org/2017/552.pdf

[2] https://eprint.iacr.org/2019/114.pdf

[3] https://eprint.iacr.org/2019/503.pdf

[4] https://eprint.iacr.org/2020/540.pdf