Cardano dApp-Wallet Web Bridge

Abstract

This documents describes a webpage-based communication bridge allowing webpages (i.e. dApps) to interface with Cardano wallets. This is done via injected javascript code into webpages. This specification defines the manner that such code is to be accessed by the webpage/dApp, as well as defining the API for dApps to communicate with the user's wallet. This document currently concerns the Shelley-Mary era but will have a second version once Plutus is supported. This specification is intended to cover similar use cases as web3 for Ethereum or EIP-0012 for Ergo. The design of this spec was based on the latter.

Motivation: why is this CIP necessary?

In order to facilitate future dApp development, we will need a way for dApps to communicate with the user's wallet. While Cardano does not yet support smart contracts, there are still various use cases for this, such as NFT management. This will also lay the groundwork for an updated version of the spec once the Alonzo hardfork is released which can extend it to allow for Plutus support.

Specification

Data Types

Address

A string representing an address in either bech32 format, or hex-encoded bytes. All return types containing Address must return the hex-encoded bytes format, but must accept either format for inputs.

Bytes

A hex-encoded string of the corresponding bytes.

cbor<T>

A hex-encoded string representing CBOR corresponding to T defined via CDDL either inside of the Shelley Multi-asset binary spec or, if not present there, from the CIP-0008 signing spec. This representation was chosen when possible as it is consistent across the Cardano ecosystem and widely used by other tools, such as cardano-serialization-lib, which has support to encode every type in the binary spec as CBOR bytes.

DataSignature

type DataSignature = {|
  signature: cbor<COSE_Sign1>,
  key: cbor<COSE_Key>,
|};

TransactionUnspentOutput

If we have CBOR specified by the following CDDL referencing the Shelley-MA CDDL:

transaction_unspent_output = [
  input: transaction_input,
  output: transaction_output,
]

then we define

type TransactionUnspentOutput = cbor<transaction_unspent_output>

This allows us to use the output for constructing new transactions using it as an output as the transaction_output in the Shelley Multi-asset CDDL does not contain enough information on its own to spend it.

Paginate

type Paginate = {|
  page: number,
  limit: number,
|};

Used to specify optional pagination for some API calls. Limits results to {limit} each page, and uses a 0-indexing {page} to refer to which of those pages of {limit} items each. dApps should be aware that if a wallet is modified between paginated calls that this will change the pagination, e.g. some results skipped or showing up multiple times but otherwise the wallet must respect the pagination order.

Extension

An extension is an object with a single field "cip" that describes a CIP number extending the API (as a plain integer, without padding). For example:

{ "cip": 30 }

Error Types

APIError

APIErrorCode {
	InvalidRequest: -1,
	InternalError: -2,
	Refused: -3,
	AccountChange: -4,
}
APIError {
	code: APIErrorCode,
	info: string
}

• InvalidRequest - Inputs do not conform to this spec or are otherwise invalid.
• InternalError - An error occurred during execution of this API call.
• Refused - The request was refused due to lack of access - e.g. wallet disconnects.
• AccountChange - The account has changed. The dApp should call wallet.enable() to reestablish connection to the new account. The wallet should not ask for confirmation as the user was the one who initiated the account change in the first place.

DataSignError

DataSignErrorCode {
	ProofGeneration: 1,
	AddressNotPK: 2,
	UserDeclined: 3,
}
type DataSignError = {
	code: DataSignErrorCode,
	info: String
}

• ProofGeneration - Wallet could not sign the data (e.g. does not have the secret key associated with the address)
• AddressNotPK - Address was not a P2PK address and thus had no SK associated with it.
• UserDeclined - User declined to sign the data

PaginateError

type PaginateError = {|
    maxSize: number,
|};

{maxSize} is the maximum size for pagination and if the dApp tries to request pages outside of this boundary this error is thrown.

TxSendError

TxSendErrorCode = {
	Refused: 1,
	Failure: 2,
}
type TxSendError = {
	code: TxSendErrorCode,
	info: String
}

• Refused - Wallet refuses to send the tx (could be rate limiting)
• Failure - Wallet could not send the tx

TxSignError

TxSignErrorCode = {
	ProofGeneration: 1,
	UserDeclined: 2,
}
type TxSignError = {
	code: TxSignErrorCode,
	info: String
}

• ProofGeneration - User has accepted the transaction sign, but the wallet was unable to sign the transaction (e.g. not having some of the private keys)
• UserDeclined - User declined to sign the transaction

Initial API

In order to initiate communication from webpages to a user's Cardano wallet, the wallet must provide the following javascript API to the webpage. A shared, namespaced cardano object must be injected into the page if it did not exist already. Each wallet implementing this standard must then create a field in this object with a name unique to each wallet containing a wallet object with the following methods. The API is split into two stages to maintain the user's privacy, as the user will have to consent to cardano.{walletName}.enable() in order for the dApp to read any information pertaining to the user's wallet with {walletName} corresponding to the wallet's namespaced name of its choice.

cardano.{walletName}.enable({ extensions: Extension[] } = {}): Promise<API>

Errors: APIError

This is the entrypoint to start communication with the user's wallet. The wallet should request the user's permission to connect the web page to the user's wallet, and if permission has been granted, the full API will be returned to the dApp to use. The wallet can choose to maintain a whitelist to not necessarily ask the user's permission every time access is requested, but this behavior is up to the wallet and should be transparent to web pages using this API. If a wallet is already connected this function should not request access a second time, and instead just return the API object.

Upon start, dApp can explicitly request a list of additional functionalities they expect as a list of CIP numbers capturing those extensions. This is used as an extensibility mechanism to document what functionalities can be provided by the wallet interface. CIP-0030 provides a set of base interfaces that every wallet must support. Then, new functionalities are introduced via additional CIPs and may be all or partially supported by wallets.

DApps are expected to use this endpoint to perform an initial handshake and ensure that the wallet supports all their required functionalities. Note that it's possible for two extensions to be mutually incompatible (because they provide two conflicting features). While we may try to avoid this as much as possible while designing CIPs, it is also the responsability of wallet providers to assess whether they can support a given combination of extensions, or not. Hence wallets aren't expected to fail should they not recognize or not support a particular combination of extensions. Instead, they should decide what they enable and reflect their choice in the response to api.getExtensions() in the Full API. As a result, dApps may fail and inform their users or may use a different, less-efficient, strategy to cope with a lack of functionality.

It is at the extension author's discretion if they wish to separate their endpoints from the base API via namespacing. Although, it is highly recommend that authors do namespace all of their extensions. If namespaced, endpoints must be preceded by .cipXXXX. from the API object, without any leading zeros.

For example; CIP-0123's endpoints should be accessed by:

api.cip123.endpoint1()
api.cip123.endpoint2()

Authors should be careful when omitting namespacing. Omission should only be considered when creating endpoints to override those defined in this specification or other extensions. Even so when overriding; the new functionality should not prevent dApps from accessing past functionality thus overriding must ensure backwards compatibility.

Any namespace omission needs to be fully justified via the proposal's Rationale section, with explanation to why it is necessary. Any potential backwards compatibility considerations should be noted to give wallets and dApps a clear unambiguous direction.

Draft or Experimental Extensions

Extensions that are draft, in development, or prototyped should not use extension naming nor should they use official namspacing until assigned a CIP number. Draft extension authors are free to test their implementation endpoints by using the Experimental API. Once a CIP number is assigned implementors should move functionality out of the experimental API.

Can extensions depend on other extensions?

Yes. Extensions may have other extensions as pre-requisite. Some newer extensions may also invalidate functionality introduced by earlier extensions. There's no particular rule or constraints in that regards. Extensions are specified as CIP, and will define what it entails to enable them.

Should extensions follow a specific format?

Yes. They all are CIPs.

Can extensions add their own endpoints and/or error codes?

Yes. Extensions may introduce new endpoints or error codes, and modify existing ones. Although, it is recommended that endpoints are namespaced. Extensions may even change the rules outlined in this very proposal. The idea being that wallet providers should start off implementing this CIP, and then walk their way to implementing their chosen extensions.

Are wallet expected to implement all extensions?

No. It's up to wallet providers to decide which extensions they ought to support.

cardano.{walletName}.isEnabled(): Promise<bool>

Errors: APIError

Returns true if the dApp is already connected to the user's wallet, or if requesting access would return true without user confirmation (e.g. the dApp is whitelisted), and false otherwise. If this function returns true, then any subsequent calls to wallet.enable() during the current session should succeed and return the API object.

cardano.{walletName}.apiVersion: String

The version number of the API that the wallet supports. Set to 1.

cardano.{walletName}.supportedExtensions: Extension[]

A list of extensions supported by the wallet. Extensions may be requested by dApps on initialization. Some extensions may be mutually conflicting and this list does not thereby reflect what extensions will be enabled by the wallet. Yet it informs on what extensions are known and can be requested by dApps if needed.

cardano.{walletName}.name: String

A name for the wallet which can be used inside of the dApp for the purpose of asking the user which wallet they would like to connect with.

cardano.{walletName}.icon: String

A URI image (e.g. data URI base64 or other) for img src for the wallet which can be used inside of the dApp for the purpose of asking the user which wallet they would like to connect with.

Full API

Upon successful connection via cardano.{walletName}.enable(), a javascript object we will refer to as API (type) / api (instance) is returned to the dApp with the following methods. All read-only methods (all but the signing functionality) should not require any user interaction as the user has already consented to the dApp reading information about the wallet's state when they agreed to cardano.{walletName}.enable(). The remaining methods api.signTx() and api.signData() must request the user's consent in an informative way for each and every API call in order to maintain security.

The API chosen here is for the minimum API necessary for dApp <-> Wallet interactions without convenience functions that don't strictly need the wallet's state to work. The API here is for now also only designed for Shelley's Mary hardfork and thus has NFT support. When Alonzo is released with Plutus support this API will have to be extended.

api.getExtensions(): Promise<Extension[]>

Errors: APIError

Retrieves the list of extensions enabled by the wallet. This may be influenced by the set of extensions requested in the initial enable request.

api.getNetworkId(): Promise<number>

Errors: APIError

Returns the network id of the currently connected account. 0 is testnet and 1 is mainnet but other networks can possibly be returned by wallets. Those other network ID values are not governed by this document. This result will stay the same unless the connected account has changed.

api.getUtxos(amount: cbor<value> = undefined, paginate: Paginate = undefined): Promise<TransactionUnspentOutput[] | null>

Errors: APIError, PaginateError

If amount is undefined, this shall return a list of all UTXOs (unspent transaction outputs) controlled by the wallet. If amount is not undefined, this request shall be limited to just the UTXOs that are required to reach the combined ADA/multiasset value target specified in amount, and if this cannot be attained, null shall be returned. The results can be further paginated by paginate if it is not undefined.

api.getCollateral(params: { amount: cbor<Coin> }): Promise<TransactionUnspentOutput[] | null>

Errors: APIError

The function takes a required object with parameters. With a single required parameter for now: amount. (NOTE: some wallets may be ignoring the amount parameter, in which case it might be possible to call the function without it, but this behavior is not recommended!). Reasons why the amount parameter is required:

1. Dapps must be motivated to understand what they are doing with the collateral, in case they decide to handle it manually.
2. Depending on the specific wallet implementation, requesting more collateral than necessarily might worsen the user experience with that dapp, requiring the wallet to make explicit wallet reorganisation when it is not necessary and can be avoided.
3. If dapps don't understand how much collateral they actually need to make their transactions work - they are placing more user funds than necessary in risk.

So requiring the amount parameter would be a by-spec behavior for a wallet. Not requiring it is possible, but not specified, so dapps should not rely on that and the behavior is not recommended.

This shall return a list of one or more UTXOs (unspent transaction outputs) controlled by the wallet that are required to reach AT LEAST the combined ADA value target specified in amount AND the best suitable to be used as collateral inputs for transactions with plutus script inputs (pure ADA-only utxos). If this cannot be attained, an error message with an explanation of the blocking problem shall be returned. NOTE: wallets are free to return utxos that add up to a greater total ADA value than requested in the amount parameter, but wallets must never return any result where utxos would sum up to a smaller total ADA value, instead in a case like that an error message must be returned.

The main point is to allow the wallet to encapsulate all the logic required to handle, maintain, and create (possibly on-demand) the UTXOs suitable for collateral inputs. For example, whenever attempting to create a plutus-input transaction the dapp might encounter a case when the set of all user UTXOs don't have any pure entries at all, which are required for the collateral, in which case the dapp itself is forced to try and handle the creation of the suitable entries by itself. If a wallet implements this function it allows the dapp to not care whether the suitable utxos exist among all utxos, or whether they have been stored in a separate address chain (see https://github.com/cardano-foundation/CIPs/pull/104), or whether they have to be created at the moment on-demand - the wallet guarantees that the dapp will receive enough utxos to cover the requested amount, or get an error in case it is technically impossible to get collateral in the wallet (e.g. user does not have enough ADA at all).

The amount parameter is required, specified as a string (BigNumber) or a number, and the maximum allowed value must be agreed to be something like 5 ADA. Not limiting the maximum possible value might force the wallet to attempt to purify an unreasonable amount of ADA just because the dapp is doing something weird. Since by protocol the required collateral amount is always a percentage of the transaction fee, it seems that the 5 ADA limit should be enough for the foreseeable future.

api.getBalance(): Promise<cbor<value>>

Errors: APIError

Returns the total balance available of the wallet. This is the same as summing the results of api.getUtxos(), but it is both useful to dApps and likely already maintained by the implementing wallet in a more efficient manner so it has been included in the API as well.

api.getUsedAddresses(paginate: Paginate = undefined): Promise<Address[]>

Errors: APIError

Returns a list of all used (included in some on-chain transaction) addresses controlled by the wallet. The results can be further paginated by paginate if it is not undefined.

api.getUnusedAddresses(): Promise<Address[]>

Errors: APIError

Returns a list of unused addresses controlled by the wallet.

api.getChangeAddress(): Promise<Address>

Errors: APIError

Returns an address owned by the wallet that should be used as a change address to return leftover assets during transaction creation back to the connected wallet. This can be used as a generic receive address as well.

api.getRewardAddresses(): Promise<Address[]>

Errors: APIError

Returns the reward addresses owned by the wallet. This can return multiple addresses e.g. CIP-0018.

api.signTx(tx: cbor<transaction>, partialSign: bool = false): Promise<cbor<transaction_witness_set>>

Errors: APIError, TxSignError

Requests that a user sign the unsigned portions of the supplied transaction. The wallet should ask the user for permission, and if given, try to sign the supplied body and return a signed transaction. If partialSign is true, the wallet only tries to sign what it can. If partialSign is false and the wallet could not sign the entire transaction, TxSignError shall be returned with the ProofGeneration code. Likewise if the user declined in either case it shall return the UserDeclined code. Only the portions of the witness set that were signed as a result of this call are returned to encourage dApps to verify the contents returned by this endpoint while building the final transaction.

api.signData(addr: Address, payload: Bytes): Promise<DataSignature>

Errors: APIError, DataSignError

This endpoint utilizes the CIP-0008 signing spec for standardization/safety reasons. It allows the dApp to request the user to sign a payload conforming to said spec. The user's consent should be requested and the message to sign shown to the user. The payment key from addr will be used for base, enterprise and pointer addresses to determine the EdDSA25519 key used. The staking key will be used for reward addresses. This key will be used to sign the COSE_Sign1's Sig_structure with the following headers set:

• alg (1) - must be set to EdDSA (-8)
• kid (4) - Optional, if present must be set to the same value as in the COSE_key specified below. It is recommended to be set to the same value as in the "address" header.
• "address" - must be set to the raw binary bytes of the address as per the binary spec, without the CBOR binary wrapper tag

The payload is not hashed and no external_aad is used.

If the payment key for addr is not a P2Pk address then DataSignError will be returned with code AddressNotPK. ProofGeneration shall be returned if the wallet cannot generate a signature (i.e. the wallet does not own the requested payment private key), and UserDeclined will be returned if the user refuses the request. The return shall be a DataSignature with signature set to the hex-encoded CBOR bytes of the COSE_Sign1 object specified above and key shall be the hex-encoded CBOR bytes of a COSE_Key structure with the following headers set:

• kty (1) - must be set to OKP (1)
• kid (2) - Optional, if present must be set to the same value as in the COSE_Sign1 specified above.
• alg (3) - must be set to EdDSA (-8)
• crv (-1) - must be set to Ed25519 (6)
• x (-2) - must be set to the public key bytes of the key used to sign the Sig_structure

api.submitTx(tx: cbor<transaction>): Promise<hash32>

Errors: APIError, TxSendError

As wallets should already have this ability, we allow dApps to request that a transaction be sent through it. If the wallet accepts the transaction and tries to send it, it shall return the transaction id for the dApp to track. The wallet is free to return the TxSendError with code Refused if they do not wish to send it, or Failure if there was an error in sending it (e.g. preliminary checks failed on signatures).

Experimental API

Multiple experimental namespaces are used:

• under api (ex: api.experimental.myFunctionality).
• under cardano.{walletName} (ex: window.cardano.{walletName}.experimental.myFunctionality)

The benefits of this are:

1. Wallets can add non-standardized features while still following the CIP30 structure
2. dApp developers can use these functions explicitly knowing they are experimental (not stable or standardized)
3. New features can be added to CIP30 as experimental features and only moved to non-experimental once multiple wallets implement it
4. It provides a clear path to updating the CIP version number (when functions move from experimental -> stable)

Rationale: how does this CIP achieve its goals?

See justification and explanations provided with each API endpoint.

Extensions

Extensions provide an extensibility mechanism and a way to negotiate (possibly conflicting) functionality between a DApp and a wallet provider. There's rules enforced as for what extensions a wallet decide to support or enable. The current mechanism only gives a way for wallets to communicate their choice back to a DApp.

We use object as extensions for now to leave room for adding fields in the future without breaking all existing interfaces. At this point in time however, objects are expected to be singleton.

Extensions can be seen as a smart versioning scheme. Except that, instead of being a monotonically increasing sequence of numbers, they are multi-dimensional feature set that can be toggled on and off at will. This is a versioning "à-la-carte" which is useful in a context where:

1. There are multiple concurrent standardization efforts on different fronts to accommodate a rapidly evolving ecosystem;
2. Not everyone agrees and has desired to support every existing standard;
3. There's a need from an API consumer standpoint to clearly identify what features are supported by providers.

Namespacing Extensions

By encouraging the explicit namespacing of each extension we aim to improve the usability of extensions for dApps. By allowing special cases where namespacing can be dropped we maintain good flexibility in extension design.

Path to Active

Acceptance Criteria

• The interface is implemented and supported by various wallet providers. See also: cardano-caniuse.
• The interface is used by DApps to interact with wallet providers. Few examples:
  • https://www.jpg.store/
  • https://app.minswap.org/
  • https://muesliswap.com/
  • https://exchange.sundaeswap.finance/
  • https://app.indigoprotocol.io/

Implementation Plan

• Provide some reference implementation of wallet providers

  • Berry-Pool/nami-wallet
  • Emurgo/yoroi-wallet

• Provide some reference implementation of the dapp connector

  • cardano-foundation/connect-with-wallet

Copyright

This CIP is licensed under CC-BY-4.0.