Wallet Chain Key Rules

Overview

In this article you'll find details on how to parse and present multichain transactions to the user so they can take an informed decision about their wallet's assets, while minimizing the number of times the user has to consent. You'll also learn how to ensure that a signature on one chain is not used to take a meaningful action on another chain.

Key derivation

When signing using chain signatures each account has an unlimited number of keys. Each key's public key is derived from the account name and the key extension which is an arbitrary string.

User's keys can be described as follow:

"david.near,"              A key with no extension
"david.near, "             A key with an extension of " "
"david.near,cold_wallet"   A key with an extension of "cold_wallet"

tip

If the keys aren't identical they have no relationship.

Ambiguous signatures

You're going to be potentially storing keys for users who hold assets on many chains. Different chains have different ways of serializing and signing transactions. Many chains take steps to ensure that their signatures are not valid signatures on other chains. EVM chains use ChainID to disambiguate signatures between different EVM chains. Dfinity uses a unique salt on the hash of the transaction.

Unfortunately, while this is a best practice, you can't guarantee that all chains do this. As such, a user could receive an innocent looking transaction on one chain that could be used to take a destructive action on another chain.

An apocryphal example:

Transaction: "7b73656e643a2022313030222c206e6f74652022227d"
Parsed SOL: claim free NFT
Parsed BTC: send 100 BTC to Attacker

The user would approve the SOL transaction but the attacker would also get the BTC transaction.

This can be solved by having different keys for any chains that you can't prove could have ambiguous transactions. This means that while an attacker may create ambiguous transactions, it will only be for wallets without assets on the target chain.

Serialization format

We're using the following format for our derivations paths.

{
   chain: number, // SLIP-44 coin type unsigned integer
   domain: String, // The domain that owns this key
   meta: any, // Catch all data structure
}

This is encoded in canonical JSON RFC 8785.

info

If you are not using a field don't make it null, don't include the key instead.

User-defined fields

For user-defined fields, the meta field can include any data you like.

tip

Do not add any extra fields at the top level, as that may clash with future versions of this specification. If needed, put them in the meta field instead.

For example, a simple way of selecting alternate keys will be using an object with an ID field:

{
    meta: {id: 10}, // Pick the tenth bitcoin key
    chain: 0,
}

Examples

Key	Description
{chain: 0, domain: "near.org"}	A bitcoin key used on near.org
{chain: 0, meta: {id: 3}}	Use the third bitcoin key

Example user flows

In the following examples, the messages are coming from the user's wallet frontend.

• Using a domains bitcoin key
• Using a personal Bitcoin key
• Using a personal EVM key to sign a Binance transaction
• Using an untyped domain key
• Using another domains Bitcoin key

tip

Wallet developers should follow this user flow format.

Using a domains bitcoin key

An application at near.org wants to sign the Bitcoin transaction Send 100 BTC using the key david.near,bitcoin,near.org,.

Signed ✅

We sign the transaction without confirmation because the key is owned by near.org.

Using a personal Bitcoin key

An application at near.org wants to sign the Bitcoin transaction Send 100 BTC using the key david.near,bitcoin,.

near.org would like to run the following Bitcoin transaction:

Send 100 BTC
[Accept] [Reject]

The user must make an informed decision about whether this is an action they would like to take.

Signed ✅

Using a personal EVM key to sign a Binance transaction

An application at near.org wants to sign the Binance Smart Chain transaction Send 100 BNB, ChainID 56 using the key david.near,evm,. The wallet knows this is a BSC transaction because of the corresponding ChainID (56) and because the evm key is being used.

near.org would like to run the following Binance Smart Chain transaction:

Send 100 BNB
[Accept] [Reject]

The user must make an informed decision about whether this is an action they would like to take.

Signed ✅

Using an untyped domain key

An application at near.org wants to sign the Bitcoin transaction Send 100 BTC using the key david.near,,near.org,.

Signed ✅

While this is ill advised, it's still the domains key so the domain can still choose whether to sign something using it.

Using another domains Bitcoin key

An application at attacker.com wants to sign the Bitcoin transaction Send 100 BTC using the key david.near,bitcoin,near.org,.

Attacker.com would like to sign a transaction using your credentials from near.org

Send 100 BTC

This is a suspicious transaction and likely not one you should accept
[Reject] [Accept (Are you sure!)]

The user must make an explicit decision to do something that is ill advised.

Signed ✅

The correct way for attacker.com to make this request is to somehow redirect the user to near.org and get the user to make a decision there.