Build a Claimable Universal Airdrop

Welcome! In this tutorial, you'll build a Universal Airdrop system that revolutionizes cross-chain token distribution. Unlike traditional airdrops that require deploying contracts on every blockchain, this universal approach lets you deploy once on Push Chain and enable users from any blockchain (Ethereum, Solana, Polygon, etc.) to claim their tokens seamlessly.

Why Universal Airdrops?

The beauty of this system lies in its efficiency and cross-chain compatibility:

• Single Deployment: Deploy your airdrop contract once on Push Chain instead of managing multiple contracts across different networks
• Cross-Chain Claims: Users from Ethereum, Solana, Polygon, and other chains can all claim tokens from the same contract
• No Multi-Chain Token Deployment: Keep your ERC-20 token on one chain while enabling universal claiming
• User Simplicity: Recipients can claim their tokens using their preferred wallet on their own chain, making the process seamless and familiar

We'll build the complete flow:

1. Generate Merkle proofs with cross-chain recipient data
2. Deploy a universal Merkle claim contract to Push Chain
3. Create a UI for recipients to claim their tokens from any chain

Full Application

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Deploy ERC-20 Token

Here are the steps to deploy the TestToken contract on Remix below:

• Set the Solidity compiler version to 0.8.22 in Remix.
• For Environment, choose Injected Provider (connect your wallet to Push Chain Donut Testnet).
• When deploying TestToken, pass constructor arguments: token name and symbol (e.g., TestToken and TEST).

Note: If you need $PC tokens to deploy the contract, you can get them from the Push Chain Faucet.

Remix IDE

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TestToken.sol

Understanding the TestToken contract

• Inherits from ERC20: Uses OpenZeppelin's battle-tested ERC20 implementation
• Constructor: Mints 1 million tokens to the deployer upon creation
• Mint function: Allows additional tokens to be minted (useful for testing)
• Standard ERC20 features: Transfer, balance checking, approvals, etc.

Deploy Universal Airdrop

Here are the steps to deploy the UniversalAirdrop contract on Remix below:

• Set the Solidity compiler version to 0.8.22 in Remix.
• For Environment, choose Injected Provider (connect your wallet to Push Chain Donut Testnet).
• When deploying UniversalAirdrop, pass constructor arguments: token address deployed in the previous step and merkle root you can get from the next step.

Note: If you need $PC tokens to deploy the contract, you can get them from the Push Chain Faucet.

Remix IDE

View on GitHub

UniversalAirdrop.sol

Understanding the UniversalAirdrop contract

• Merkle Proof Verification: Uses OpenZeppelin's MerkleProof.verify() to validate inclusion proofs
• Universal Support: Accepts any recipient address format (the proof generation handles the conversion)
• Reentrancy Protection: Uses ReentrancyGuard to prevent reentrancy attacks
• Claim Tracking: Maps claim IDs (address + origin chain) to prevent double claims per recipient per origin chain
• Owner Controls: Allows updating the Merkle root for future airdrop rounds

Generate Merkle Tree

In this part, we'll create a Merkle proof generator that produces cryptographic proofs for a universal airdrop system. This generator will create a Merkle tree from recipient data and generate proofs that can be verified on-chain.

The dependencies you'll need for the Merkle proof generator:

• @openzeppelin/merkle-tree: Core library for building Merkle trees with cryptographic hashing
• viem: Ethereum library providing keccak256 hashing and ABI encoding utilities
• bs58: Base58 encoding/decoding library for Solana addresses

VIRTUAL NODE IDE

Each entry in the array represents a recipient with:

• recipient: Wallet address (format varies by blockchain)
• chainNamespace: Blockchain type ("eip155", "solana", "push", etc.)
• chainId: Specific chain identifier within that namespace
• amount: Token amount in smallest units (as string to avoid precision issues)

How the Merkle proof works

The proof allows anyone to verify that a specific recipient is included in the airdrop without revealing the entire recipient list. The smart contract can verify the proof by:

1. Recalculating the leaf hash from the recipient's data
2. Using the provided proof hashes to reconstruct the path to the root
3. Comparing the reconstructed root with the stored merkleRoot

✅ Next steps: You'll use the merkleRoot when deploying the UniversalAirdrop contract, and the frontend will use each recipient's proof array to submit claims on-chain.

Conclusion

You generated Merkle proofs from an airdrop list, deployed a Universal Merkle‑verified airdrop contract to Push Chain Donut Testnet, and added a claim UI. With this universal airdrop system, users from different chains can claim their tokens seamlessly using Push Chain's Universal External Accounts (UEA) system.