x/accounts Module

The x/accounts module enhances the Cosmos SDK by providing tools and infrastructure for creating advanced smart accounts.

The Authentication Interface

x/accounts introduces the Authentication interface, allowing for flexible transaction (TX) authentication beyond traditional public key cryptography.

Chain developers can implement tailored authentication methods for their accounts. Any account that implements the Authentication interface can be authenticated within a transaction.

To implement the Authentication interface in x/accounts, an account must expose an execution handler capable of processing a specific message type.

The key message type for authentication is MsgAuthenticate, which is defined in the module's protocol buffer files:

interfaces/account_abstraction/v1/interface.proto

Authentication Mechanism

AnteHandler in the SDK

The Cosmos SDK utilizes an AnteHandler to verify transaction (TX) integrity. Its primary function is to ensure that the messages within a transaction are correctly signed by the purported sender.

Authentication Flow for x/accounts Module

When the AnteHandler identifies that a message sender (and transaction signer) belongs to the x/accounts module, it delegates the authentication process to that module.

Authentication Interface Requirement

For successful authentication, the account must implement the Authentication interface. If an account fails to implement this interface, it's considered non-externally owned, resulting in transaction rejection.

Sequence Diagram

graph TD
    A[Tx Is Received] --> B[Execute Signature Verification Ante Handler]
    B --> D{Is signer an x/accounts account?}
    D -->|No| E[Continue with signature verification ante handler]
    D -->|Yes| F{Does account handle MsgAuthenticate?}
    F -->|No| G[Fail TX: Non-externally owned account]
    F -->|Yes| H[Invoke signer account MsgAuthenticate]
    E --> I[End]
    G --> I
    H --> I

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Implementing the Authentication Interface

To implement the Authentication interface, an account must handle the execution of MsgAuthenticate. Here's an example of how to do this:

package base

import (
   "context"
   "errors"
   aa_interface_v1 "github.com/cosmos/cosmos-sdk/x/accounts/interfaces/account_abstraction/v1"
   "github.com/cosmos/cosmos-sdk/x/accounts/std"
)

// Account represents a base account structure
type Account struct {
   // Account fields...
}

// Authenticate implements the authentication flow for an abstracted base account.
func (a Account) Authenticate(ctx context.Context, msg *aa_interface_v1.MsgAuthenticate) (*aa_interface_v1.MsgAuthenticateResponse, error) {
   if !accountstd.SenderIsAccountsModule(ctx) {
      return nil, errors.New("unauthorized: only accounts module is allowed to call this")
   }
   // Implement your authentication logic here
   // ...
   return &aa_interface_v1.MsgAuthenticateResponse{}, nil
}

// RegisterExecuteHandlers registers the execution handlers for the account.
func (a Account) RegisterExecuteHandlers(builder *accountstd.ExecuteBuilder) {
   accountstd.RegisterExecuteHandler(builder, a.SwapPubKey) // Other handlers
   accountstd.RegisterExecuteHandler(builder, a.Authenticate) // Implements the Authentication interface
}

Key Implementation Points

1. Sender Verification: Always verify that the sender is the x/accounts module. This prevents unauthorized accounts from triggering authentication.
2. Authentication Safety: Ensure your authentication mechanism is secure:
   • Prevent replay attacks by making it impossible to reuse the same action with the same signature.

Implementation example

Please find an example here.

Supporting Custom Accounts in the x/auth gRPC Server

Overview

The x/auth module provides a mechanism for custom account types to be exposed via its Account and AccountInfo gRPC queries. This feature is particularly useful for ensuring compatibility with existing wallets that have not yet integrated with x/accounts but still need to parse account information post-migration.

Implementation

To support this feature, your custom account type needs to implement the auth.QueryLegacyAccount handler. Here are some important points to consider:

1. Selective Implementation: This implementation is not required for every account type. It's only necessary for accounts you want to expose through the x/auth gRPC Account and AccountInfo methods.
2. Flexible Response: The info field in the QueryLegacyAccountResponse is optional. If your custom account cannot be represented as a BaseAccount, you can leave this field empty.

Example Implementation

A concrete example of implementation can be found in defaults/base/account.go. Here's a simplified version:

func (a Account) AuthRetroCompatibility(ctx context.Context, _ *authtypes.QueryLegacyAccount) (*authtypes.QueryLegacyAccountResponse, error) {
    seq := a.GetSequence()
    num := a.GetNumber()
    address := a.GetAddress()
    pubKey := a.GetPubKey()

    baseAccount := &authtypes.BaseAccount{
        AccountNumber: num,
        Sequence:      seq,
        Address:       address,
    }

    // Convert pubKey to Any type
    pubKeyAny, err := gogotypes.NewAnyWithValue(pubKey)
    if err != nil {
        return nil, err
    }
    baseAccount.PubKey = pubKeyAny

    // Convert the entire baseAccount to Any type
    accountAny, err := gogotypes.NewAnyWithValue(baseAccount)
    if err != nil {
        return nil, err
    }

    return &authtypes.QueryLegacyAccountResponse{
        Account: accountAny,
        Info:    baseAccount,
    }, nil
}

Usage Notes

• Implement this handler only for account types you want to expose via x/auth gRPC methods.
• The info field in the response can be nil if your account doesn't fit the BaseAccount structure.

Genesis

Creating accounts on genesis

In order to create accounts at genesis, the x/accounts module allows developers to provide a list of genesis MsgInit messages that will be executed in the x/accounts genesis flow.

The init messages are generated offline. You can also use the following CLI command to generate the json messages: simd accounts tx init [account type] [msg] --from me --genesis. This will generate a jsonified init message wrapped in an x/accounts MsgInit.

This follows the same initialization flow and rules that would happen if the chain is running. The only concrete difference is that this is happening at the genesis block.

For example, given the following genesis.json file:

{
  "app_state": {
    "accounts": {
      "init_account_msgs": [
        {
          "sender": "account_creator_address",
          "account_type": "lockup",
          "message": {
            "@type": "cosmos.accounts.defaults.lockup.MsgInitLockupAccount",
            "owner": "some_owner",
            "end_time": "..",
            "start_time": ".."
          },
          "funds": [
            {
              "denom": "stake",
              "amount": "1000"
            }
          ]
        }
      ]
    }
  }
}

The accounts module will run the lockup account initialization message.