Implementing Chain Signatures

Chain signatures enable NEAR accounts, including smart contracts, to sign and execute transactions across many blockchain protocols. This unlocks the next level of blockchain interoperability by giving ownership of diverse assets, cross-chain accounts, and data to a single NEAR account.

Supported Networks

While you can sign transactions for any network using Eddsa or Ecdsa keys, each chain signs transactions differently.Our example implementation shows you how to sign transactions for: Bitcoin, Solana, Cosmos, XRP, Aptos, Sui and EVM networks (Ethereum, Base, BNB Chain, Avalanche, Polygon, Arbitrum, and more).

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Create a Chain Signature

There are five steps to create a Chain Signature:

1. Deriving the Foreign Address - Derive the address that will be controlled on the target blockchain.
2. Creating a Transaction - Create the transaction or message to be signed.
3. Requesting a Signature - Call the NEAR MPC contract requesting it to sign the transaction.
4. Formatting the Signature - Format the signature from the MPC contract and add it to the transaction.
5. Relaying the Signed Transaction - Send the signed transaction to the destination chain for execution.

Diagram of a chain signature in NEAR The chainsig.js library provides a convenient interface for completing each of these steps.

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Chain Signatures Contract

To interact with the chain signatures library you first need to instantiate a ChainSignaturesContract. The networkId and contractId are set to the values specified in the previous section depending which network you are on.

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Chain Adapters

To interact with a specific chain, you need to instantiate the relevant chainAdapter.

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1. Deriving the Foreign Address

Chain Signatures use derivation paths to represent accounts on the target blockchain. The foreign address to be controlled can be deterministically derived from:

• The NEAR account calling the MPC contract (e.g., example.near, example.testnet, etc.)
• A derivation path (a string such as ethereum-1, ethereum-2, etc.)
• The MPC service’s master public key (we don’t need to worry about this as it is defined in the library we’re using).

To derive the address call the deriveAddressAndPublicKey method passing the near account Id from which the address is being derived and the derivation path.

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2. Creating the Transaction

To construct the transaction to be signed use the method prepareTransactionForSigning.

EVM Function Calls

To call a function on a smart contract we need the ABI of the contract, in our repo this is defined in the config.js file (this can be gathered from Remix or using Etherscan).Then define a Contract object using the ethers libraryThen to construct the transactionThis approach allows you to call smart contract functions by encoding the function data and including it in the transaction.

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3. Requesting the Signature

Once the transaction is created and ready to be signed, a signature request is made by calling sign on the MPC smart contract. The method requires four parameters:

1. The payloads (or hashes) to be signed for the target blockchain
2. The derivation path for the account we want to use to sign the transaction
3. The keyType, Ecdsa for Secp256k1 signatures and Eddsa for Ed25519 signatures.
4. The signerAccount which contains the accountId that is signing and the signAndSendTransactions function from Near Connect.

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4. Formatting the Signature

Once the signature is returned from the MPC it needs to be formatted and added to the transaction to produce a signed transaction.

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5. Relaying the Signed Transaction

Now that we have a signed transaction, we can relay it to the target network using broadcastTx. The method returns a transaction hash which can be used to locate the transaction on an explorer.