EIP-3085 - wallet_addEthereumChain RPC Method

Abstract

This EIP adds a wallet-namespaced RPC method: wallet_addEtherereumChain, providing a standard interface for adding chains to Ethereum wallets.

Specification

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119.

This proposal defines a new RPC method, wallet_addEthereumChain.

wallet_addEthereumChain

The wallet_addEthereumChain method is used to suggest to the wallet that a new chain be added to the wallet's list of chains. It takes a single parameter and returns null if the chain was added successfully, or an error if the chain was not added.

wallet_addEthereumChain Parameters

The wallet_addEthereumChain method takes a single parameter, an EthereumChainAddRequest object, which is defined as follows:

interface AddEthereumChainParameter {
  chainId: string;
  blockExplorerUrls?: string[];
  chainName?: string;
  iconUrls?: string[];
  nativeCurrency?: {
    name: string;
    symbol: string;
    decimals: number;
  };
  rpcUrls?: string[];
}

Only the chainId is required per this specification, but a wallet MAY require any other fields listed, impose additional requirements on them, or ignore them outright.

If a field does not meet the requirements of this specification and the wallet does not ignore the field, the wallet MUST reject the request.

The chainId is the integer ID of the chain as a hexadecimal string, as per EIP-155. The blockExplorerUrls, iconUrls, and rpcUrls fields are arrays of strings, each of which MUST be a valid URL. The nativeCurrency field is an object with name, symbol, and decimals fields, where decimals is a non-negative integer, and is to be interpreted like in EIP-20. The chainName field is a string that is the human-readable name of the chain.

The wallet MUST reject the request if the chainId is not a valid hexadecimal string, or if the chainId is not a valid chain ID.

The wallet MUST reject the request if the rpcUrls field is not provided, or if the rpcUrls field is an empty array. The wallet MUST reject the request if the rpcUrls contains any strings that are not valid URLs. The wallet must reject the request if the chainId does not match the value of the eth_chainId method for any of the RPC urls.

The wallet MUST reject the request if the nativeCurrency field is provided, and any of the name, symbol, or decimals fields are missing. The wallet MUST reject the request if the decimals field is a negative integer.

The wallet MUST reject the request if the blockExplorerUrls field is provided, and any of the URLs are not valid URLs.

The wallet MUST reject the request if the iconUrls field is provided, and any of the URLs are not valid URLs or do not point to a valid image.

The wallet MUST reject any URLs that use the file: or http: schemes.

wallet_addEthereumChain Returns

The method MUST return null if the request was successful, and an error otherwise. The wallet MAY reject the request for any reason.

The chain MUST NOT be assumed to be automatically selected by the wallet, even if the wallet does not reject the request.

A request to add a chain that was already added SHOULD be successful, unless the user declines the request or the validation fails.

The wallet MUST NOT allow the same chainId to be added multiple times. See Security Considerations for more information.

Rationale

The design of wallet_addEthereumChain is deliberately ignorant of what it means to "add" a chain to a wallet. The meaning of "adding" a chain to a wallet depends on the wallet implementation.

When calling the method, specifying the chainId will always be necessary, since in the universe of Ethereum chains, the EIP-155 chain ID is effectively the chain GUID. The remaining parameters amount to what, in the estimation of the authors, a wallet will minimally require in order to effectively support a chain and represent it to the user. The network ID (per the net_version RPC method) is omitted since it is effectively superseded by the chain ID.

For security reasons, a wallet should always attempt to validate the chain metadata provided by the requester, and may choose to fetch the metadata elsewhere entirely. Either way, only the wallet can know which chain metadata it needs from the requester in order to "add" the chain. Therefore, all parameters except chainId are specified as optional, even though a wallet may require them in practice.

This specification does not mandate that the wallet "switches" its "active" or "currently selected" chain after a successful request, if the wallet has a concept thereof. Just like the meaning of "adding" a chain, "switching" between chains is a wallet implementation detail, and therefore out of scope.

Security Considerations

wallet_addEthereumChain is a powerful method that exposes the end user to serious risks if implemented incorrectly. Many of these risks can be avoided by validating the request data in the wallet, and clearly disambiguating different chains in the wallet UI.

Chain IDs

Since the chain ID used for transaction signing determines which chain the transaction is valid for, handling the chain ID correctly is of utmost importance. The wallet should:

• Ensure that a submitted chain ID is valid.
• It should be a 0x-prefixed hexadecimal string per EIP-695, and parse to an integer number.
• Prevent the same chain ID from being added multiple times.
• See the next section for how to handle multiple RPC endpoints.
• Only use the submitted chain ID to sign transactions, never a chain ID received from an RPC endpoint.
• A malicious or faulty endpoint could return arbitrary chain IDs, and potentially cause the user to sign transactions for unintended chains.
• Verify that the specified chain ID matches the return value of eth_chainId from the endpoint, as described above.

RPC Endpoints and RPC URLs

Wallets generally interact with chains via an RPC endpoint, identified by some URL. Most wallets ship with a set of chains and corresponding trusted RPC endpoints. The endpoints identified by the rpcUrls parameter cannot be assumed to be honest, correct, or even pointing to the same chain. Moreover, even trusted endpoints can expose users to privacy risks depending on their data collection practices.

Therefore, the wallet should:

• Inform users that their on-chain activity and IP address will be exposed to RPC endpoints.
• If an endpoint is unknown to the wallet, inform users that the endpoint may behave in unexpected ways.
• Observe good web security practices when interacting with the endpoint, such as require HTTPS.
• Clearly inform the user which RPC URL is being used to communicate with a chain at any given moment, and inform the user of the risks of using multiple RPC endpoints to interact with the same chain.

Validating Chain Data

A wallet that implements wallet_addEthereumChain should expect to encounter requests for chains completely unknown to the wallet maintainers. That said, community resources exist that can be leveraged to verify requests for many Ethereum chains. The wallet should maintain a list of known chains, and verify requests to add chains against that list. Indeed, a wallet may even prefer its own chain metadata over anything submitted with a wallet_addEthereumChain request.

UX

Adding a new chain to the wallet can have significant implications for the wallet's functionality and the experience of the user. A chain should never be added without the explicit consent of the user, and different chains should be clearly differentiated in the wallet UI. In service of these goals, the wallet should:

• When receiving a wallet_addEthereumChain request, display a confirmation informing the user that a specific requester has requested that the chain be added.
• Ensure that any chain metadata, such as nativeCurrency and blockExplorerUrls, are validated and used to maximum effect in the UI.
• If any images are provided via iconUrls, ensure that the user understands that the icons could misrepresent the actual chain added.
• If the wallet UI has a concept of a "currently selected" or "currently active" chain, ensure that the user understands when a chain added using wallet_addEthereumChain becomes selected.

Preserving User Privacy

Although a request to add a chain that was already added should generally be considered a success, treating such requests as automatic successes leaks information to requesters about the chains a user has added to their wallet. In the interest of preserving user privacy, implementers of wallet_addEthereumChain should consider displaying user confirmations even in these cases. If the user denies the request, the wallet should return the same user rejection error as normal so that requesters cannot learn which chains are supported by the wallet without explicit permission to do so.

Copyright

Copyright and related rights waived via CC0.