Specification Overview

THIS SECTION IS NOT NORMATIVE

3.1 Prerequisites

According to W3C specifications and as a requirement for the deigns of this method, the DID needs to fulfil the basic premise principles listed below:

• A Permanent identifier (URN).

• Be cryptographically verifiable.

• Be decentralised (no central registration authority required).

• Easy and economical to create.

• The DID is always required to resolve (associated with) to a DID Document.

• The DID Subject is not always the administrator of its DID. It depends on use case scenario.

Similarly, the DID Document needs to satisfy the following:

• The DID Document needs to be publicly available.

• The DID Document must contain:

  • One or more keys to authenticate the DID subject.

  • One or more Services associated with DID subject.

  • Additional metadata like digital signatures, timestamps, and other cryptographic proofs.

3.2 UTXO DID Method

In this section we present an overview of the DID method. Our proposal introduces a new Decentralized Identifier (DID) method that links a UTXO and the DID with the public key of the subject and manages the DID status and revocation through transaction spending checks. We use the BSV Blockchain as the verifiable data registry.

The UTXO DID method uses the following method name: bsv

3.2.1 The DID

The issuance of a DID using this method is performed by publishing a blockchain transaction:Tx0. This transaction has a single input and a single output. The transaction ID (TxID) becomes the DID for the subject. The TxID can be easily calculated by either controller or subject and, because of the properties of blockchain it would never be repeated. It is also easily recognisable by independent third-party platforms, such as blockchain explorers.

1. Representation of a DID as per W3C specification

DID:example:123456789abcdefghi

Where fields are broken down as follows:

Scheme	DID Method	DID Method-Specific Identifier
DID:	example:	123456789abcdefghi

2. Representation of a DID using UTXO method

DID:bsv:21f2dae26817752b8f92c51a49a898e287ad133a4e7ed64b4909f7b62f0bbb6e

Where fields are broken down as follows:

Scheme	DID Method	DID Method-Specific Identifier
DID:	Blockchain	TXID
DID:	bsv:	21f2dae26817752b8f92c51a49a898e287ad133a4e7ed64b4909f7b62f0bbb6e

3.2.2 The DID Document

The DID Document is published via a subsequent transaction Tx1 that spends the output of Tx0. The relationship between the DID, the DID document, and the blockchain transactions is given in Figure 1. The transaction Tx1 contains a single input and a single output. The output contains the locking script, the DID Document and the funds covering the mining fee of the next transaction. Tx1 spending the output of Tx0 allows an external observer to conclude that there is a link between both blockchain transactions. The status of Tx1 output indicates the latest status of the DID Document.

Figure 1: DID UTXO Status

3.2.2.1 The DID Document Data Model

Our current implementation uses W3C DID Document Data Model and is referenced in the DID Document. Below is a representative example of a DID Document data model.

"@context": "https://www.w3.org/ns/did/v1", 
  "id": "did:bsv:5909468ac49f960e191faba2dd7da60bd1775ccf59e90b8390c971d04741b710",
  "controller": "did:bsv:b6333300b727ae4d355ffe2fee06ebe9ed5565cb1321e02637fa971bd523272e",
  "verificationMethod": 
         [ { 
             "id": "did:bsv:5909468ac49f960e191faba2dd7da60bd1775ccf59e90b8390c971d04741b710#subject-key",
             "type": "JsonWebKey2020", 
             "controller": "did:bsv:5909468ac49f960e191faba2dd7da60bd1775ccf59e90b8390c971d04741b710",
             "publicKeyJwk": 
              { 
                  "kty": "EC", 
                  "x": "xJxFTwL183Hmz19WnLAgBa1wpljMuaYk_rBnAKlol-g", 
                  "y": "585wM9i1dGHr6qgL5NG5N2EAxel3Son9HpkGpl-hY-I", 
                  "crv": "secp256k1" 
              } } ]
  "authentication": [ "did:bsv:5909468ac49f960e191faba2dd7da60bd1775ccf59e90b8390c971d04741b710#subject-key" ]