did:ckb

The did:ckb method is a Decentralized Identifier (DID) specification that leverages the CKB blockchain to create, manage, and resolve DIDs. It provides a decentralized way to establish digital identities with strong security guarantees.

At its core, did:ckb uses CKB’s unique Cell model to store DID metadata on the blockchain. Unlike traditional account-based blockchains, CKB uses a UTXO (Unspent Transaction Output) system where data is stored in “Cells” - flexible containers that can hold both value and arbitrary data.

The did:ckb achieves several key goals:

Decentralization: No central authority controls identity creation or management
Persistence: Identity data is permanently stored on the blockchain
Verifiability: All operations are cryptographically verifiable
Interoperability: Compatible with W3C DID standards

The formal specification for did:ckb can be found in the wip-01.

A mainnet-live implementation is available at the did-ckb-contract.

How DIDs are Created

A did:ckb identifier looks like this: did:ckb:qq2m72a2vas4e5ovcpxoedscguuu4nba

The identifier is generated through a deterministic process that ensures uniqueness:

A transaction is created that includes a special “DID Metadata Cell”
The cell contains the identity information and rules for future updates
A unique identifier is derived from transaction details using cryptographic hashing and type-id
The result is encoded in base32 format

This process guarantees that each DID is unique and tied to a specific blockchain transaction.

Core Operations

Creating a DID

To create a new did:ckb identity:

Define your identity metadata (verification methods, services, aliases)
Set up authorization rules (who can update this DID)
Create a CKB transaction that stores this data in a new Cell
Submit the transaction to the network

The DID becomes active once the transaction is confirmed on the blockchain.

Resolving a DID

When someone wants to verify or use your DID:

The resolver extracts the identifier from the DID string
Searches the blockchain for the corresponding DID Metadata Cell
Retrieves the stored identity information
Converts it to standard DID Document format

Since the did:ckb is type-id based, it has unique identifiers tied to specific blockchain transactions hence no duplicates.

Updating a DID

To modify your identity information:

Create a new transaction that consumes the current DID Cell
Generate a new Cell with updated metadata
Authorize the transaction using the current ownership rules
Submit to the network

The update maintains the same DID identifier while changing the underlying data.

Deactivating a DID

To permanently disable a DID:

Create a transaction that consumes the DID Cell without creating a replacement
Authorize using current ownership rules
Submit to the network

Warning: Deactivation is irreversible. Once a DID is deactivated, it cannot be reactivated.

Protecting Against Attacks

Double-spending: Prevented by CKB’s UTXO model and POW consensus
Key compromise: Mitigated through multi-signature and quantum-resistant options
Front-running: Impossible due to identifier generation from transaction inputs
Denial of service: Economic protections via transaction fees

Privacy Features

did:ckb provides privacy through:

Pseudonymous identifiers: DIDs don’t reveal personal information
Selective disclosure: Users control what information to share
Multiple identities: Users can maintain separate DIDs for different contexts

Privacy Considerations

Correlation risks: Transaction patterns might link different uses of the same DID
Metadata leakage: Transaction details could reveal information

Users should use separate DIDs for different purposes and consider privacy-enhancing techniques like transaction mixing.

Understanding CKB Cells

To fully grasp did:ckb, it’s helpful to understand CKB’s Cell model:

Cell Basics

A Cell is CKB’s fundamental storage unit, containing:

Capacity: Storage space and value (measured in CKBytes)
Data: Arbitrary content (like DID metadata)
Lock Script: Controls who can use the Cell
Type Script: Defines how the Cell can be modified

Live vs Dead Cells

Live Cells: Available for use in new transactions
Dead Cells: Already consumed and cannot be reused

DID updates work by consuming the old Cell and creating a new one with the same identifier.

Transactions

CKB transactions represent state changes:

Consume existing Cells as inputs
Create new Cells as outputs
Scripts validate all operations

This model ensures that DID operations are atomic and verifiable.

Integration with Web5

did:ckb is designed to work seamlessly with the broader Web5 ecosystem, providing a blockchain-based identity layer that complements other off-chain components.

The protocol’s compatibility with did:plc metadata format means it can leverage existing tooling and libraries for DID document generation and verification.