Cross-Chain BLS Signature Verification dApp (Part 2)

Part 2: Creating a Signature Verification Precompile Contract

Precompiled contracts are a way to execute code written in the low-level coding language Go from the EVM. Go is much faster and more efficient than Solidity. If you are familiar with Python programming, you might be familiar with a similar concept. Many Python functions and libraries are written in the programming language C, since it is much more efficient than Python.

Goal:

The task here is to write a precompile that can verify a BLS signature for a message and a BLS Public Key.

Part 1 of this assessment is located here: Create a Cross-Chain dApp with Verification.

Learn about Precompile-EVM

To get a comprehensive introduction to Precompile-EVM, take the Avalanche Academy course on Customizing the EVM.

Precompile-EVM

Precompile-EVM is a repository for registering precompiles to Subnet-EVM without forking the Subnet-EVM codebase. Subnet-EVM supports registering external precompiles through precompile/modules package. By importing Subnet-EVM as a library, you can register your own precompiles to Subnet-EVM and build it together with Subnet-EVM.

Environment Setup

To effectively build, run, and test Precompile-EVM, the following is a (non-exhaustive) list of dependencies that you will need:

• Golang
• Node.js
• AvalancheGo
• Avalanche Network Runner

To get started easily, we provide a Dev Container specification, that can be used using GitHub Codespace or locally using Docker and VS Code. DevContainers are a concept that utilizes containerization (via Docker containers) to create consistent and isolated development environment. We can access this environment through VS code, which allows for the development experience to feel as if you were developing locally..

Dev Container in Codespace

Codespaces is a development environment service offered by GitHub that allows developers to write, run, test, and debug their code directly on a cloud machine provided by GitHub. The developer can edit the code through a VS Code running in the browser or locally.

To run a Codespace click on the Code and switch to the Codespaces tab. There, click Create Codespace on branch [...].

Local Dev Container

In order to run the Dev Container locally:

• Install VS Code, Docker and the Dev Container Extension
• Clone the Repository
• Open the Container by issuing the Command "Dev Containers: Reopen in Container" in the VS Code command palette (on Mac-OS, run [Cmd + Shift + P]).

How to use

There is an example branch hello-world-example in this repository. You can check the example branch to see how to register precompiles and test them.

Generate Precompile Files

First, you need to create your precompile contract interface in the contracts directory and build the ABI. Then you can generate your precompile files with ./scripts/generate_precompile.sh --abi {abiPath} --out {outPath}. This script installs the precompilegen tool from Subnet-EVM and runs it to generate your precompile.

Register Precompile

In plugin/main.go Subnet-EVM is already imported and ready to be Run from the main package. All you need to do is explicitly register your precompiles to Subnet-EVM in plugin/main.go and build it together with Subnet-EVM. Precompiles generated by precompilegen tool have a self-registering mechanism in their module.go/init() function. All you need to do is to force-import your precompile packprecompile package in plugin/main.go.

Build

You can build your precompile and Subnet-EVM with ./scripts/build.sh. This script builds Subnet-EVM, and your precompile together and generates a binary file. The binary file is compatible with AvalancheGo plugins.

Run

You can run you Precompile-EVM by using the Avalanche CLI.

First, create the configuration for your subnet.

avalanche subnet create mysubnet --custom --vm $AVALANCHEGO_PLUGIN_PATH/srEXiWaHuhNyGwPUi444Tu47ZEDwxTWrbQiuD7FmgSAQ6X7Dy --genesis ./.devcontainer/genesis-example.json

Next, launch the Subnet with your custom VM:

avalanche subnet deploy mysubnet

Test

You can create contract tests in contracts/test with the Hardhat test framework. These can be run by adding ginkgko test cases in tests/precompile/solidity/suites.go and a suitable genesis file in tests/precompile/genesis. You can install AvalancheGo binaries with ./scripts/install_avalanchego_release.sh then run the tests with ./scripts/run_ginkgo.sh

Changing Versions

In order to upgrade the Subnet-EVM version, you need to change the version in go.mod and scripts/versions.sh. You can also change the AvalancheGo version through scripts/versions.sh as well. Then you can run ./scripts/build.sh to build the plugin with the new version.

AvalancheGo Compatibility

[v0.1.0-v0.1.1] AvalancheGo@v1.10.1-v1.10.4 (Protocol Version: 26)
[v0.1.2] AvalancheGo@v1.10.5-v1.10.8 (Protocol Version: 27)
[v0.1.3] AvalancheGo@v1.10.9-v1.10.12 (Protocol Version: 28)
[v0.1.4] AvalancheGo@v1.10.9-v1.10.12 (Protocol Version: 28)
[v0.1.5] AvalancheGo@v1.10.13-v1.10.14 (Protocol Version: 29)
[v0.1.6] AvalancheGo@v1.10.15-v1.10.17 (Protocol Version: 30)
[v0.1.7] AvalancheGo@v1.10.15-v1.10.17 (Protocol Version: 30)
[v0.1.8] AvalancheGo@v1.10.18-v1.10.19 (Protocol Version: 31)
[v0.2.0] AvalancheGo@v1.11.0-v1.11.1 (Protocol Version: 33)
[v0.2.1] AvalancheGo@v1.11.3-v1.11.7 (Protocol Version: 35)
[v0.2.2] AvalancheGo@v1.11.3-v1.11.7 (Protocol Version: 35)
[v0.2.3] AvalancheGo@v1.11.3-v1.11.7 (Protocol Version: 35)