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Note: Mainnet-beta, testnet, devnet gateway program address:

ZETAjseVjuFsxdRxo6MmTCvqFwb3ZHUx56Co3vCmGis

The PDA account address (derived from seeds b"meta" and canonical bump) is

2f9SLuUNb7TNeM6gzBwT4ZjbL5ZyKzzHg1Ce9yiquEjj

The PDA account address (derived from seeds `b"rent-payer")

Am1aA3XQciu3vMG6E9yLa2Y9TcTf2XB3D3akLtjVzu3L

Introduction

This repository hosts the smart contract (program) deployed on the Solana network to enable ZetaChain's cross-chain functionality. It consists of a single program that supports the following actions:

  1. Users on the Solana network can send SOL to the program to deposit into ZetaChain, with the option to invoke a ZetaChain EVM contract.
  2. Contracts on the ZetaChain EVM can withdraw SOL to users on the Solana network.

Build and Test Instructions

Prerequisites: a recent version of rust compiler and cargo package manger must be installed. The program is built with the anchor framework so it needs to be installed as well; see installation

Please install compatible Solana tools and anchor-cli before build, otherwise the program will not be built successfully

$ solana-install init 1.18.15

$ cargo install --git https://github.com/coral-xyz/anchor --tag v0.30.0 anchor-cli --locked

To show the installed versions of the tools

$ cargo-build-sbf --version
solana-cargo-build-sbf 1.18.15
platform-tools v1.41
rustc 1.75.0

$ anchor --version
anchor-cli 0.30.0

To build (this will require at least 2GB disk space)

$ anchor build

To run the tests

$ anchor test

Authentication and Authorization

Anyone can deposit and remote invoke ZetaChain contracts.

Only ZetaChain TSS account can call withdraw on the program. The ZetaChain TSS account is a collection of Observer/Signers which uses ECDSA TSS (Threshold Signature Scheme) to sign outbound transactions. The TSS address will appear in this program a single ECDSA secp256k1 address; but it does not have a single private key, rather its private key consists of multiple key shares and they collectively sign a message in a KeySign MPC ceremony. The program authenticates via verifying the TSS signature and is authorized by ZetaChain to perform outbound transactions as part of ZetaChain cross-chain machinery.

The ZetaChain TSS is on ECDSA secp256k1 curve; But Solana native digital signature scheme is EdDSA Ed25519 curve. Therefore the program uses custom logic to verify the TSS ECDSA signature (like alternative authentication in smart contract wallet); the native transaction signer (fee payer on Solana) does not carry authorization and it's only used to build the transaction and pay tx fees. There are no restrictions on who the native transaction signer/fee payer is. The following code excerpt is for authenticating TSS signature in the contract itself, using the Rust secp256k1 library bundled with solana:

protocol-contracts-solana/programs/protocol-contracts-solana/src/lib.rs

Lines 116 to 121 in 01eeb97

let address = recover_eth_address(&message_hash, recovery_id, &signature)?; // ethereum address is the last 20 Bytes of the hashed pubkey
msg!("recovered address {:?}", address);
if address != pda.tss_address {
msg!("ECDSA signature error");
return err!(Errors::TSSAuthenticationFailed);
}

The function recover_eth_address is implemented in the gateway program:

protocol-contracts-solana/programs/protocol-contracts-solana/src/lib.rs

Lines 180 to 196 in 01eeb97

fn recover_eth_address(
message_hash: &[u8; 32],
recovery_id: u8,
signature: &[u8; 64],
) -> Result<[u8; 20]> {
let pubkey = secp256k1_recover(message_hash, recovery_id, signature)
.map_err(|_| ProgramError::InvalidArgument)?;
// pubkey is 64 Bytes, uncompressed public secp256k1 public key
let h = hash(pubkey.to_bytes().as_slice()).to_bytes();
let address = &h.as_slice()[12..32]; // ethereum address is the last 20 Bytes of the hashed pubkey
msg!("recovered address {:?}", address);
let mut eth_address = [0u8; 20];
eth_address.copy_from_slice(address);
Ok(eth_address)
}

The TSS signature is a ECDSA secp256k1 signature; its public key therefore address (Ethereum compatible hashing from pubkey) is therefore verifiable using the secp256k1_recover function. Alternatively, Solana runtime also provides a program to provide this verification service via CPI; see proposal 48 which might be more cost efficient.

In the instruction, the ECDSA signed message_hash must commit to the nonce, amount, and to address. See the check in these instructions like:

protocol-contracts-solana/programs/protocol-contracts-solana/src/lib.rs

Lines 110 to 114 in 01eeb97

let mut concatenated_buffer = Vec::new();
concatenated_buffer.extend_from_slice(&nonce.to_be_bytes());
concatenated_buffer.extend_from_slice(&amount.to_be_bytes());
concatenated_buffer.extend_from_slice(&ctx.accounts.to.key().to_bytes());
require!(message_hash == hash(&concatenated_buffer[..]).to_bytes(), Errors::MessageHashMismatch);
The commitment of nonce in the signature prevents replay of the TSS ECDSA signed message. Also (to be added in #6) a chain id of Solana should be added to the commitment of the message hash, so that the signature cannot be replayed on other blockchains that potentially uses similar authentication (say in TON).

Relevant Account and Addresses

The Gateway program derive a PDA (Program Derived Address) with seeds b"meta" and canonical bump. This PDA account/address actually holds the SOL balance of the Gateway program. For SPL tokens, the program stores the SPL token in PDA derived ATAs. For each SPL token (different mint account), the program creates ATA from PDA and the Mint (standard way of deriving ATA in Solana SPL program).

The PDA account itself is a data account that holds Gateway program state, namely the following data types

protocol-contracts-solana/programs/protocol-contracts-solana/src/lib.rs

Lines 271 to 275 in 01eeb97

pub struct Pda {
nonce: u64, // ensure that each signature can only be used once
tss_address: [u8; 20], // 20 bytes address format of ethereum
authority: Pubkey,
}

The nonce is incremented on each successful withdraw transaction, and it's used to prevent replay of signed ECDSA messages. The tss_address is the TSS address of ZetaChain (20Bytes, Ethereum style). authority is the one who can update the TSS address stored in PDA account. The initialize instruction sets nonce to 0.

Troubleshooting

MacOS error when running anchor test or solana-test-validator

If you see errors like

Unable to get latest blockhash. Test validator does not look started. Check ".anchor/test-ledger/test-ledger-log.txt" for errors. Consider increasing [test.startup_wait] in Anchor.toml.

or

% solana-test-validator --reset
Ledger location: test-ledger
Log: test-ledger/validator.log
Error: failed to start validator: Failed to create ledger at test-ledger: io error: Error checking to unpack genesis archive: Archive error: extra entry found: "._genesis.bin" Regular

This is because the BSD tar program is not compatible with the GNU tar program.

To fix the issue: install GNU tar program using homebrew and export it's executable path in your .zshrc file:

Mac with Apple Silicon

brew install gnu-tar
# Put this in ~/.zshrc 
export PATH="/opt/homebrew/opt/gnu-tar/libexec/gnubin:$PATH"

Intel-based Mac

brew install gnu-tar
# Put this in ~/.zshrc 
export PATH="/usr/local/opt/gnu-tar/libexec/gnubin:$PATH"

see https://solana.stackexchange.com/questions/4499/blockstore-error-when-starting-solana-test-validator-on-macos-13-0-1/16319#16319