RFC 004: Accounts

Changelog

• 17/03/2023: DRAFT
• 09/05/2023: DRAFT 2

Context

The current implementation of accounts in the Cosmos SDK is limiting in terms of functionality, extensibility, and overall architecture. This RFC aims to address the following issues with the current account system:

1. Accounts Representation and Authentication Mechanism

The current SDK accounts are represented as google.Protobuf.Any, which are then encapsulated into the account interface. This account interface essentially represents the authentication mechanism, as it implements methods such as GetNumber and GetSequence that serve as abstractions over the authentication system. However, this approach restricts the scope and functionality of accounts within the SDK.

2. Limited Account Interface

The account interface in its current form is not versatile enough to accommodate more advanced account functionalities, such as implementing vesting capabilities or more complex authentication and authorization systems.

3. Multiple Implementations of the Account Interface

There are several implementations of the account interface, like ModuleAccount, but the existing abstraction does not allow for meaningful differentiation between them. This hinders the ability to create specialized accounts that cater to specific use cases.

4. Primitive Authorization System

The authorization system in the x/auth module is basic and defines authorizations solely for the functionalities of the x/bank module. Consequently, although the state transition authorization system is defined in x/auth, it only covers the use cases of x/bank, limiting the system's overall scope and adaptability.

5. Cyclic Dependencies and Abstraction Leaks

The current account system leads to cyclic dependencies and abstraction leaks throughout the Cosmos SDK. For instance, the Vesting functionality belongs to the x/auth module, which depends on the x/bank module. However, the x/bank module depends on the x/auth module again to identify the account type (either Vesting or Base) during a coin transfer. This dependency structure creates architectural issues and complicates the overall design of the SDK.

Proposal

This proposal aims to transform the way accounts are managed within the Cosmos SDK by introducing significant changes to their structure and functionality.

Rethinking Account Representation and Business Logic

Instead of representing accounts as simple google.Protobuf.Any structures stored in state with no business logic attached, this proposal suggests a more sophisticated account representation that is closer to module entities. In fact, accounts should be able to receive messages and process them in the same way modules do, and be capable of storing state in a isolated (prefixed) portion of state belonging only to them, in the same way as modules do.

Account Message Reception

We propose that accounts should be able to receive messages in the same way modules can, allowing them to manage their own state modifications without relying on other modules. This change would enable more advanced account functionality, such as the VestingAccount example, where the x/bank module previously needed to change the vestingState by casting the abstracted account to VestingAccount and triggering the TrackDelegation call. Accounts are already capable of sending messages when a state transition, originating from a transaction, is executed.

When accounts receive messages, they will be able to identify the sender of the message and decide how to process the state transition, if at all.

Consequences

These changes would have significant implications for the Cosmos SDK, resulting in a system of actors that are equal from the runtime perspective. The runtime would only be responsible for propagating messages between actors and would not manage the authorization system. Instead, actors would manage their own authorizations. For instance, there would be no need for the x/auth module to manage minting or burning of coins permissions, as it would fall within the scope of the x/bank module.

The key difference between accounts and modules would lie in the origin of the message (state transition). Accounts (ExternallyOwnedAccount), which have credentials (e.g., a public/private key pairing), originate state transitions from transactions. In contrast, module state transitions do not have authentication credentials backing them and can be caused by two factors: either as a consequence of a state transition coming from a transaction or triggered by a scheduler (e.g., the runtime's Begin/EndBlock).

By implementing these proposed changes, the Cosmos SDK will benefit from a more extensible, versatile, and efficient account management system that is better suited to address the requirements of the Cosmos ecosystem.

Standardization

With x/accounts allowing a modular api there becomes a need for standardization of accounts or the interfaces wallets and other clients should expect to use. For this reason we will be using the CIP repo in order to standardize interfaces in order for wallets to know what to expect when interacting with accounts.

Implementation

Account Definition

We define the new Account type, which is what an account needs to implement to be treated as such. An Account type is defined at APP level, so it cannot be dynamically loaded as the chain is running without upgrading the node code, unless we create something like a CosmWasmAccount which is an account backed by an x/wasm contract.

// Account is what the developer implements to define an account.
type Account[InitMsg proto.Message] interface {
    // Init is the function that initialises an account instance of a given kind.
    // InitMsg is used to initialise the initial state of an account.
    Init(ctx *Context, msg InitMsg) error
    // RegisterExecuteHandlers registers an account's execution messages.
    RegisterExecuteHandlers(executeRouter *ExecuteRouter)
    // RegisterQueryHandlers registers an account's query messages.
    RegisterQueryHandlers(queryRouter *QueryRouter)
    // RegisterMigrationHandlers registers an account's migration messages.
    RegisterMigrationHandlers(migrationRouter *MigrationRouter)
}

The InternalAccount definition

The public Account interface implementation is then converted by the runtime into an InternalAccount implementation, which contains all the information and business logic needed to operate the account.

type Schema struct {
    state StateSchema // represents the state of an account
    init InitSchema // represents the init msg schema
    exec ExecSchema // represents the multiple execution msg schemas, containing also responses
    query QuerySchema // represents the multiple query msg schemas, containing also responses
    migrate *MigrateSchema // represents the multiple migrate msg schemas, containing also responses, it's optional
}

type InternalAccount struct {
    init    func(ctx *Context, msg proto.Message) (*InitResponse, error)
    execute func(ctx *Context, msg proto.Message) (*ExecuteResponse, error)
    query   func(ctx *Context, msg proto.Message) (proto.Message, error)
    schema  func() *Schema
    migrate func(ctx *Context, msg proto.Message) (*MigrateResponse, error)
}

This is an internal view of the account as intended by the system. It is not meant to be what developers implement. An example implementation of the InternalAccount type can be found in this example of account whose credentials can be recovered. In fact, even if the Internal implementation is untyped (with respect to proto.Message), the concrete implementation is fully typed.

During any of the execution methods of InternalAccount, schema excluded, the account is given a Context which provides:

• A namespaced KVStore for the account, which isolates the account state from others (NOTE: no store keys needed, the account address serves as store key).
• Information regarding itself (its address)
• Information regarding the sender.
• ...

Init

Init defines the entrypoint that allows for a new account instance of a given kind to be initialised. The account is passed some opaque protobuf message which is then interpreted and contains the instructions that constitute the initial state of an account once it is deployed.

An Account code can be deployed multiple times through the Init function, similar to how a CosmWasm contract code can be deployed (Instantiated) multiple times.

Execute

Execute defines the entrypoint that allows an Account to process a state transition, the account can decide then how to process the state transition based on the message provided and the sender of the transition.

Query

Query defines a read-only entrypoint that provides a stable interface that links an account with its state. The reason for which Query is still being preferred as an addition to raw state reflection is to:

• Provide a stable interface for querying (state can be optimised and change more frequently than a query)
• Provide a way to define an account Interface with respect to its Read/Write paths.
• Provide a way to query information that cannot be processed from raw state reflection, ex: compute information from lazy state that has not been yet concretely processed (eg: balances with respect to lazy inputs/outputs)

Schema

Schema provides the definition of an account from API perspective, and it's the only thing that should be taken into account when interacting with an account from another account or module, for example: an account is an authz-interface account if it has the following message in its execution messages MsgProxyStateTransition{ state_transition: google.Protobuf.Any }.

Migrate

Migrate defines the entrypoint that allows an Account to migrate its state from a previous version to a new one. Migrations can be initiated only by the account itself, concretely this means that the migrate action sender can only be the account address itself, if the account wants to allow another address to migrate it on its behalf then it could create an execution message that makes the account migrate itself.

x/accounts module

In order to create accounts we define a new module x/accounts, note that x/accounts deploys account with no authentication credentials attached to it which means no action of an account can be incepted from a TX, we will later explore how the x/authn module uses x/accounts to deploy authenticated accounts.

This also has another important implication for which account addresses are now fully decoupled from the authentication mechanism which makes in turn off-chain operations a little more complex, as the chain becomes the real link between account identifier and credentials.

We could also introduce a way to deterministically compute the account address.

Note, from the transaction point of view, the init_message and execute_message are opaque google.Protobuf.Any.

The module protobuf definition for x/accounts are the following:

// Msg defines the Msg service.
service Msg {
  rpc Deploy(MsgDeploy) returns (MsgDeployResponse);
  rpc Execute(MsgExecute) returns (MsgExecuteResponse);
  rpc Migrate(MsgMigrate) returns (MsgMigrateResponse);
}

message MsgDeploy {
  string sender = 1;
  string kind = 2;
  google.Protobuf.Any init_message = 3;
  repeated google.Protobuf.Any authorize_messages = 4 [(gogoproto.nullable) = false];
}

message MsgDeployResponse {
  string address = 1;
  uint64 id = 2;
  google.Protobuf.Any data = 3;
}

message MsgExecute {
  string sender = 1;
  string address = 2;
  google.Protobuf.Any message = 3;
  repeated google.Protobuf.Any authorize_messages = 4 [(gogoproto.nullable) = false];
}

message MsgExecuteResponse {
  google.Protobuf.Any data = 1;
}

message MsgMigrate {
  string sender = 1;
  string new_account_kind = 2;
  google.Protobuf.Any migrate_message = 3;
}

message MsgMigrateResponse {
  google.Protobuf.Any data = 1;
}

MsgDeploy

Deploys a new instance of the given account kind with initial settings represented by the init_message which is a google.Protobuf.Any. Of course the init_message can be empty. A response is returned containing the account ID and humanised address, alongside some response that the account instantiation might produce.

Address derivation

In order to decouple public keys from account addresses, we introduce a new address derivation mechanism which is

MsgExecute

Sends a StateTransition execution request, where the state transition is represented by the message which is a google.Protobuf.Any. The account can then decide if to process it or not based on the sender.

MsgMigrate

Migrates an account to a new version of itself, the new version is represented by the new_account_kind. The state transition can only be incepted by the account itself, which means that the sender must be the account address itself. During the migration the account current state is given to the new version of the account, which then executes the migration logic using the migrate_message, it might change state or not, it's up to the account to decide. The response contains possible data that the account might produce after the migration.

Authorize Messages

The Deploy and Execute messages have a field in common called authorize_messages, these messages are messages that the account can execute on behalf of the sender. For example, in case an account is expecting some funds to be sent from the sender, the sender can attach a MsgSend that the account can execute on the sender's behalf. These authorizations are short-lived, they live only for the duration of the Deploy or Execute message execution, or until they are consumed.

An alternative would have been to add a funds field, like it happens in cosmwasm, which guarantees the called contract that the funds are available and sent in the context of the message execution. This would have been a simpler approach, but it would have been limited to the context of MsgSend only, where the asset is sdk.Coins. The proposed generic way, instead, allows the account to execute any message on behalf of the sender, which is more flexible, it could include NFT send execution, or more complex things like MsgMultiSend or MsgDelegate, etc.

Further discussion

Sub-accounts

We could provide a way to link accounts to other accounts. Maybe during deployment the sender could decide to link the newly created to its own account, although there might be use-cases for which the deployer is different from the account that needs to be linked, in this case a handshake protocol on linking would need to be defined.

Predictable address creation

We need to provide a way to create an account with a predictable address, this might serve a lot of purposes, like accounts wanting to generate an address that:

• nobody else can claim besides the account used to generate the new account
• is predictable

For example:

message MsgDeployPredictable {
  string sender = 1;
  uint32 nonce = 2; 
  ...
}

And then the address becomes bechify(concat(sender, nonce))

x/accounts would still use the monotonically increasing sequence as account number.

Joining Multiple Accounts

As developers are building new kinds of accounts, it becomes necessary to provide a default way to combine the functionalities of different account types. This allows developers to avoid duplicating code and enables end-users to create or migrate to accounts with multiple functionalities without requiring custom development.

To address this need, we propose the inclusion of a default account type called "MultiAccount". The MultiAccount type is designed to merge the functionalities of other accounts by combining their execution, query, and migration APIs. The account joining process would only fail in the case of API (intended as non-state Schema APIs) conflicts, ensuring compatibility and consistency.

With the introduction of the MultiAccount type, users would have the option to either migrate their existing accounts to a MultiAccount type or extend an existing MultiAccount with newer APIs. This flexibility empowers users to leverage various account functionalities without compromising compatibility or resorting to manual code duplication.

The MultiAccount type serves as a standardized solution for combining different account functionalities within the cosmos-sdk ecosystem. By adopting this approach, developers can streamline the development process and users can benefit from a modular and extensible account system.