Method Specification for Ethereum

did:etho

Summary

Decentralized identifiers (DIDs) are a new type of identifiers that enables verifiable, self-sovereign digital identity. This ETHO DID method specification describes a new DID method, that is, ETHO DID and defines how Ethereum blockchain stores ETHO DIDs and their corresponding DID documents, and how to do CRUD operations on ETHO DID documents.

This specification conforms to the requirements specified in the DIDs specification currently published by the W3C Credentials Community Group.

The full DID ETHO specification can be found here.

ETHO DID Method Name

The name-string that shall identify this DID method is: etho.

A DID that uses this method MUST begin with the following prefix: did:etho. Per this DID specification, this string MUST be in lowercase.

The remainder of the DID, after the prefix, is its namespace-specific identifier specified below.

Namespace Specific Identifier (NSI)

The namespace specific identifier is defined by the following ABNF:

etho-did   = "did:etho:" etho-specific-idstring
etho-specific-idstring = 40*40HEXDIG

Example

A valid ETHO DID might be:

did:etho:1f4B9d871fed2dEcb2670A80237F7253DB5766De

CRUD Operations

The following section outlines the DID operations for the did:etho method.

ETHO DIDs reside on the Ethereum blockchain, and are managed via the ETHO DID management smart contract.

For the sake of convenience, we refer to the ETHO DID management smart contract as 'the registry'.

Create (Register)

The ETHO DID creation is implicit and it does not require any interaction with the registry.

A subject who has an Ethereum address need not invoke any method and will automatically own an ETHO DID that concatenating "did:etho:" and the Ethereum address without a 0x prefix.

For instance, Alice, who has an Ethereum address 0x1f4B9d871fed2dEcb2670A80237F7253DB5766De, will automatically become the subject of did:etho:1f4B9d871fed2dEcb2670A80237F7253DB5766De.

Read (Resolve)

ETHO DID's associated DID document can be looked up by invoking the getDocument method of the registry.

To ensure the smart contract invocation result is trustworthy, the client could query a certain number of nodes and then compare the return values or deploy its own node.

The interface method for resolving an ETHO DID document is defined as follows:

get_document()

Besides this full-fledged resolver, the ETHO blockchain provides other simple resolvers, such as fetching the authentication property.

ETHO DID Document Example

{
  "@context": ["https://www.w3.org/ns/did/v1"],
  "id": "did:etho:1f4B9d871fed2dEcb2670A80237F7253DB5766De",
  "publicKey": [
	{
	  "id": "did:etho:1f4B9d871fed2dEcb2670A80237F7253DB5766De#keys-1",
	  "type": "EcdsaSecp256k1RecoveryMethod2020",
	  "controller": "did:etho:1f4B9d871fed2dEcb2670A80237F7253DB5766De",
	  "ethereumAddress": "0x1f4B9d871fed2dEcb2670A80237F7253DB5766De"
	}
  ],
  "authentication": [
	"did:etho:1f4B9d871fed2dEcb2670A80237F7253DB5766De#keys-1"
  ]
}

Update (Replace)

To update an ETHO DID document, the corresponding ETHO DID subject just need to invoke relevant functions.

For instance, the ETHO DID subject can invoke the addController method to add a delegate which has the authorization to insert a new verification method into the authentication property of the delegated ETHO DID.

The interface method for adding a delegate ETHO DID is defined as follows:

add_controller(delegate: String)

The delegate parameter specifies the to-be-added controller.

Similarly, the interface method for removing a delegate ETHO DID is defined as follows:

remove_controller(delegate: String)

The delegate parameter specifies the to-be-removed controller.

Here we do not provide the full list of supported update methods and will provide specific documentation which lists all of the related APIs.

Delete (Revoke)

To delete (or deactivate) an ETHO DID, it suffices to remove all the verification methods from its associated DID document and set a flag in the registry to indicate the DID is deactivated. In this case, there is no authentication method that can be used to authenticate the holder's identity.

The interface method for deactivating an ETHO DID document is defined as follows:

deactivate_did(did: String)

The did parameter specifies the to-be-deactivated ETHO DID.

More importantly, the deletion of an ETHO DID implies this DID cannot be registered or reactivated again.

Security and Privacy Considerations

There are several securities and privacy considerations that implementers would want to take into consideration when implementing this specification.

The current ETHO DID implementation does not allow an Ethereum address to have multiple ETHO DIDs, and if the ETHO DID is deactivated, the corresponding Ethereum address cannot access the deactivated ETHO DID. Hence, it loses all capability to perform operations on that ETHO DID.

Since the delegates specified in the controller property can change the value of authentication, they have the same privileges as the DID subject.

ETHO DID documents should be limited to verification methods and service endpoints, and should not store any personal information.

Reference Implementations

The reference implementation is available here: https://github.com/ontology-tech/DID-solidity/tree/etho-did

References

[1]. Ethereum github, https://github.com/ethereum

[2]. W3C Decentralized Identifiers (DIDs) v1.0, https://w3c.github.io/did-core/