digitalbazaardid:key method driver (@digitalbazaar/did-method-key)
A DID (Decentralized Identifier) method driver for the
did-iolibrary and for standalone use
Table of Contents
Background
See also (related specs):
A did:key method driver for the did-io
client library and for standalone use.
The did:key method is used to express public keys in a way that doesn't
require a DID Registry of any kind. Its general format is:
did:key:<multibase encoded, multicodec identified, public key>So, for example, the following DID would be derived from a base-58 encoded ed25519 public key:
did:key:z6MkpTHR8VNsBxYAAWHut2Geadd9jSwuBV8xRoAnwWsdvktHThat DID would correspond to the following DID Document:
Example DID Document
{
"@context": [
"https://www.w3.org/ns/did/v1",
"https://w3id.org/security/suites/ed25519-2020/v1",
"https://w3id.org/security/suites/x25519-2020/v1"
],
"id": "did:key:z6MkpTHR8VNsBxYAAWHut2Geadd9jSwuBV8xRoAnwWsdvktH",
"verificationMethod": [
{
"id": "did:key:z6MkpTHR8VNsBxYAAWHut2Geadd9jSwuBV8xRoAnwWsdvktH#z6MkpTHR8VNsBxYAAWHut2Geadd9jSwuBV8xRoAnwWsdvktH",
"type": "Ed25519VerificationKey2020",
"controller": "did:key:z6MkpTHR8VNsBxYAAWHut2Geadd9jSwuBV8xRoAnwWsdvktH",
"publicKeyMultibase": "z6MkpTHR8VNsBxYAAWHut2Geadd9jSwuBV8xRoAnwWsdvktH"
}
],
"authentication": [
"did:key:z6MkpTHR8VNsBxYAAWHut2Geadd9jSwuBV8xRoAnwWsdvktH#z6MkpTHR8VNsBxYAAWHut2Geadd9jSwuBV8xRoAnwWsdvktH"
],
"assertionMethod": [
"did:key:z6MkpTHR8VNsBxYAAWHut2Geadd9jSwuBV8xRoAnwWsdvktH#z6MkpTHR8VNsBxYAAWHut2Geadd9jSwuBV8xRoAnwWsdvktH"
],
"capabilityDelegation": [
"did:key:z6MkpTHR8VNsBxYAAWHut2Geadd9jSwuBV8xRoAnwWsdvktH#z6MkpTHR8VNsBxYAAWHut2Geadd9jSwuBV8xRoAnwWsdvktH"
],
"capabilityInvocation": [
"did:key:z6MkpTHR8VNsBxYAAWHut2Geadd9jSwuBV8xRoAnwWsdvktH#z6MkpTHR8VNsBxYAAWHut2Geadd9jSwuBV8xRoAnwWsdvktH"
],
"keyAgreement": [
{
"id": "did:key:z6MkpTHR8VNsBxYAAWHut2Geadd9jSwuBV8xRoAnwWsdvktH#z6LSbysY2xFMRpGMhb7tFTLMpeuPRaqaWM1yECx2AtzE3KCc",
"type": "X25519KeyAgreementKey2020",
"controller": "did:key:z6MkpTHR8VNsBxYAAWHut2Geadd9jSwuBV8xRoAnwWsdvktH",
"publicKeyMultibase": "z6LSbysY2xFMRpGMhb7tFTLMpeuPRaqaWM1yECx2AtzE3KCc"
}
]
}Security
The keyAgreement key is a Curve25519 public key (suitable for
Diffie-Hellman key exchange) that is deterministically derived from the source
Ed25519 key, using ed2curve-js.
Note that this derived key is optional -- there's at least one proof that this is safe to do.
Install
Requires Node.js 16+
To install from npm:
npm install --save @digitalbazaar/did-method-keyTo install locally (for development):
git clone https://github.com/digitalbazaar/did-method-key.git
cd did-method-key
npm installUsage
use()
This method registers a multibase-multikey header and a multibase-multikey deserializer and configures a driver to use a multibase-multikey deserializer to handle data using that multibase-multikey header.
import * as EcdsaMultikey from '@digitalbazaar/ecdsa-multikey';
import {driver} from '@digitalbazaar/did-method-key';
const didKeyDriverMultikey = driver();
didKeyDriverMultikey.use({
multibaseMultikeyHeader: 'zDna',
fromMultibase: EcdsaMultikey.from
});createFromMultibase()
This utility function can be used to adapt legacy verification suites such as
Ed25519VerificationSuite2018 to work properly with fromMultibase()
calls in DidKeyDriver.
import {driver} from '@digitalbazaar/did-method-key';
import {Ed25519VerificationKey2018} from
'@digitalbazaar/ed25519-verification-key-2018';
const didKeyDriver2018 = driver();
didKeyDriver2018.use({
multibaseMultikeyHeader: header,
fromMultibase: createFromMultibase(Ed25519VerificationKey2018)
});fromKeyPair()
To generate a new key and get its corresponding did:key method DID Document
from a verification keypair.
import {driver} from '@digitalbazaar/did-method-key';
import {Ed25519VerificationKey2020} from
'@digitalbazaar/ed25519-verification-key-2020';
const didKeyDriver = driver();
didKeyDriver.use({
multibaseMultikeyHeader: 'z6Mk',
fromMultibase: Ed25519VerificationKey2020.from
});
const publicKeyMultibase = 'z6MkpTHR8VNsBxYAAWHut2Geadd9jSwuBV8xRoAnwWsdvktH';
const verificationKeyPair = await Ed25519VerificationKey2020.from({
publicKeyMultibase
});
// or perhaps:
// const verificationKeyPair = await Ed25519VerificationKey2020.generate();
const {didDocument, keyPairs, methodFor} = await didKeyDriver.fromKeyPair({
verificationKeyPair
});
// print the DID Document above
console.log(JSON.stringify(didDocument, null, 2));
// keyPairs will be set like so =>
Map(2) {
'did:key:z6MknCCLeeHBUaHu4aHSVLDCYQW9gjVJ7a63FpMvtuVMy53T#z6MknCCLeeHBUaHu4aHSVLDCYQW9gjVJ7a63FpMvtuVMy53T' => Ed25519VerificationKey2020 {
id: 'did:key:z6MknCCLeeHBUaHu4aHSVLDCYQW9gjVJ7a63FpMvtuVMy53T#z6MknCCLeeHBUaHu4aHSVLDCYQW9gjVJ7a63FpMvtuVMy53T',
controller: 'did:key:z6MknCCLeeHBUaHu4aHSVLDCYQW9gjVJ7a63FpMvtuVMy53T',
revoked: undefined,
type: 'Ed25519VerificationKey2020',
publicKeyMultibase: 'z6MknCCLeeHBUaHu4aHSVLDCYQW9gjVJ7a63FpMvtuVMy53T',
privateKeyMultibase: undefined
},
'did:key:z6MknCCLeeHBUaHu4aHSVLDCYQW9gjVJ7a63FpMvtuVMy53T#z6LSotGbgPCJD2Y6TSvvgxERLTfVZxCh9KSrez3WNrNp7vKW' => X25519KeyAgreementKey2020 {
id: 'did:key:z6MknCCLeeHBUaHu4aHSVLDCYQW9gjVJ7a63FpMvtuVMy53T#z6LSotGbgPCJD2Y6TSvvgxERLTfVZxCh9KSrez3WNrNp7vKW',
controller: 'did:key:z6MknCCLeeHBUaHu4aHSVLDCYQW9gjVJ7a63FpMvtuVMy53T',
revoked: undefined,
type: 'X25519KeyAgreementKey2020',
publicKeyMultibase: 'z6LSotGbgPCJD2Y6TSvvgxERLTfVZxCh9KSrez3WNrNp7vKW',
privateKeyMultibase: undefined
}
}methodFor is a convenience function that returns a key pair instance that
contains publicKeyMultibase for given purpose. For example, a verification key
(containing a signer() and verifier() functions) are frequently useful for
jsonld-signatures or
vc-js operations. After generating
a new did:key DID, you can do:
// For signing Verifiable Credentials
const assertionKeyPair = methodFor({purpose: 'assertionMethod'});
// For Authorization Capabilities (zCaps)
const invocationKeyPair = methodFor({purpose: 'capabilityInvocation'});
// For Encryption using `@digitalbazaar/minimal-cipher`
const keyAgreementPair = methodFor({purpose: 'keyAgreement'});Note that methodFor returns a key pair that contains a publicKeyMultibase.
This makes it useful for verifying and encrypting operations.
publicKeyToDidDoc()
If you already have an Ed25519VerificationKey2020 public key object (as an
LDKeyPair instance, or a plain key description object), you can turn it into
a DID Document:
const {didDocument} = await didKeyDriver.publicKeyToDidDoc({publicKeyDescription});get()
Getting a full DID Document from a did:key DID
To get a DID Document for an existing did:key DID:
const did = 'did:key:z6MknCCLeeHBUaHu4aHSVLDCYQW9gjVJ7a63FpMvtuVMy53T';
const didDocument = await didKeyDriver.get({did});(Results in the example DID Doc above).
Getting the DID Document from key id
You can also use a .get() to retrieve an individual key, if you know its id
already (this is useful for constructing documentLoaders for JSON-LD Signature
libs, and the resulting key does include the appropriate @context).
const verificationKeyId = 'did:key:z6MknCCLeeHBUaHu4aHSVLDCYQW9gjVJ7a63FpMvtuVMy53T#z6MknCCLeeHBUaHu4aHSVLDCYQW9gjVJ7a63FpMvtuVMy53T';
const keyAgreementKeyId = 'did:key:z6MknCCLeeHBUaHu4aHSVLDCYQW9gjVJ7a63FpMvtuVMy53T#z6LSotGbgPCJD2Y6TSvvgxERLTfVZxCh9KSrez3WNrNp7vKW';
const didDocument = await didKeyDriver.get({url: verificationKeyId});
// OR
const didDocument = await didKeyDriver.get({url: keyAgreementKeyId});
// DID Document ->
console.log(JSON.stringify(didDocument, null, 2));publicMethodFor()
Often, you have just a did:key DID, and you need to get a key for a
particular purpose from it, such as an assertionMethod key to verify a
VC signature, or a keyAgreement key to encrypt a document for that DID's
controller.
For that purpose, you can use a combination of get() and publicMethodFor:
// Start with the DID
const didDocument = await didKeyDriver.get({did});
// This lets you use `publicMethodFor()` to get a key for a specific purpose
const keyAgreementMethod = didKeyDriver.publicMethodFor({
didDocument, purpose: 'keyAgreement'
});
const assertionMethod = didKeyDriver.publicMethodFor({
didDocument, purpose: 'assertionMethod'
});
// If you have a known key type, for example, `Ed25519VerificationKey2020`,
// you can create key instances which allow you to get access to a
// `verify()` function.
const assertionMethodPublicKey = await Ed25519VerificationKey2020.from(
assertionMethod);
const {verify} = assertionMethodPublicKey.verifier();publicMethodFor will throw an error if no key is found for a given purpose.
Contribute
See the contribute file!
PRs accepted.
If editing the Readme, please conform to the standard-readme specification.
Commercial Support
Commercial support for this library is available upon request from Digital Bazaar: support@digitalbazaar.com
License
New BSD License (3-clause) © Digital Bazaar