Understanding DIDs

What is DID?

DID is a unique identity address calculated from a set of credentials, and we extend DID as unique identifiers for everything in ArcBlock Ecosystem, such as:

Account
Token
NFT
NFT Factory
Stake
Delegation
Blocklet
Server

How to Create DID?

Tip

Please note that sometimes the terms DID and address is used interchangeably in this documentation.

DID Notation

A typical DID provided by ArcBlock looks like this:

did:abt:z1muQ3xqHQK2uiACHyChikobsiY5kLqtShA
  DID            DID String
schema

DID Type

Bitcoin and Ethereum use secp256k1 for the public key encryption of their wallets, to generate the wallet address, they used fixed hash algorithms. In ArcBlock, we make this process flexible and extensible - developers and users can choose their favorite algorithm combination. For example, by default, we use ED25519 for public key encryption, SHA3 for public key hashing, and base58 for address encoding.

To make sure the address contains the info about the algorithm combination, we pack this algorithm combination as DID Type and include them in the DID generating process.

DID type is the first 2 bytes of the DID string's binary format. It contains three sections:

The first six bits are the RoleType of DID, e.g., account = 0
The following 5 bits denote the KeyType, the algorithm to convert the secret key to the public key, e.g., ED25519 = 0
The latter 5 bits represent the HashType function to calculate the hash of the public key, e.g., SHA3 = 1

So DID type bytes 0x0C01 can be interpreted as follows:

+-------------+-----------+------------+
| 000011      | 00000     | 00001      |
+-------------+-----------+------------+
| application | ed25519   | sha3       |
+-------------+-----------+------------+

See Appendix for the full list of RoleType, KeyType and HashType.

DID Generate Algorithm

It's calculated with the following algorithm:

Step 1: Choose the RoleType, KeyType and Hash from above, let's use application, ed25519 and sha3 in this example.
Step 2: Choose a secret key randomly, e.g. javascript D67C071B6F51D2B61180B9B1AA9BE0DD0704619F0E30453AB4A592B036EDE644E4852B7091317E3622068E62A5127D1FB0D4AE2FC50213295E10652D2F0ABFC7
Step 3: Generate the public key of this secret key by using the KeyType. So we can get public key javascript E4852B7091317E3622068E62A5127D1FB0D4AE2FC50213295E10652D2F0ABFC7
Step 4: Get the Hash of the public key javascript EC8E681514753FE5955D3E8B57DAEC9D123E3DB146BDDFC3787163F77F057C27
Step 5: Take the first 20 bytes of the public key hash javascript EC8E681514753FE5955D3E8B57DAEC9D123E3DB1
Step 6: Add the DID type bytes 0x0C01 in front of the hash of Step 4 javascript 0C01EC8E681514753FE5955D3E8B57DAEC9D123E3DB1
Step 7: Get the hash of the extended hash in Step 6 javascript 42CD815145538F8003586C880AF94418341F9C4B8FA0394876553F8A952C7D03
Step 8: Take the first 4 bytes in step 7 javascript 42CD8151
Step 9: Append the 4 bytes in step 8 to the extended hash in step 6. This is the binary DID string javascript 0C01EC8E681514753FE5955D3E8B57DAEC9D123E3DB142CD8151
Step 10: Encode the binary value by using the Bitcoin Base58 method. Note, we are using IPFS's multibase to encode as base58_btc type, it will add a z in the beginning of the base58 encoded string javascript zNKtCNqYWLYWYW3gWRA1vnRykfCBZYHZvzKr
Step 11: Assemble the parts and get the full DID javascript did:abt:zNKtCNqYWLYWYW3gWRA1vnRykfCBZYHZvzKr

For a detailed explanation of the algorithm, please check out ArcBlock DID Explained

Appendix

RoleType

const RoleType = {
  ROLE_ACCOUNT: 0,
  ROLE_NODE: 1,
  ROLE_DEVICE: 2,
  ROLE_APPLICATION: 3,
  ROLE_SMART_CONTRACT: 4,
  ROLE_BOT: 5,
  ROLE_ASSET: 6,
  ROLE_STAKE: 7,
  ROLE_VALIDATOR: 8,
  ROLE_GROUP: 9,
  ROLE_TX: 10,
  ROLE_TETHER: 11,
  ROLE_SWAP: 12,
  ROLE_DELEGATION: 13,
  ROLE_VC: 14,
  ROLE_BLOCKLET: 15,
  ROLE_STORE: 16,
  ROLE_TOKEN: 17,
  ROLE_FACTORY: 18,
  ROLE_ROLLUP: 19,
  ROLE_STORAGE: 20,
  ROLE_ANY: 63,
};

KeyType

const KeyType = {
  ED25519: 0,
  SECP256K1: 1,
  ETHEREUM: 2,
};

HashType

const HashType = {
  KECCAK: 0,
  SHA3: 1,
  KECCAK_384: 2,
  SHA3_384: 3,
  KECCAK_512: 4,
  SHA3_512: 5,
  SHA2: 6,
};

References

W3C DID Core