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Always set alg and kid on expansion #502

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40 changes: 37 additions & 3 deletions packages/dids/src/methods/did-dht.ts
Original file line number Diff line number Diff line change
Expand Up @@ -32,6 +32,7 @@ import { extractDidFragment } from '../utils.js';
import { DidError, DidErrorCode } from '../did-error.js';
import { DidVerificationRelationship } from '../types/did-core.js';
import { EMPTY_DID_RESOLUTION_RESULT } from '../types/did-resolution.js';
import { getJoseSignatureAlgorithmFromPublicKey } from '@web5/crypto/utils';

/**
* Represents a BEP44 message, which is used for storing and retrieving data in the Mainline DHT
Expand Down Expand Up @@ -347,6 +348,15 @@ export enum DidDhtRegisteredKeyType {
secp256r1 = 2
}

/**
* Private helper that maps did dht registered key types to their corresponding default algorithm identifiers.
*/
const KeyTypeToDefaultAlgorithmMap = {
[DidDhtRegisteredKeyType.Ed25519] : 'EdDSA',
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[DidDhtRegisteredKeyType.secp256k1] : 'ES256K',
[DidDhtRegisteredKeyType.secp256r1] : 'ES256',
} as const;
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/**
* Maps {@link https://www.w3.org/TR/did-core/#verification-relationships | DID Core Verification Relationship}
* values to the corresponding record name in the DNS packet representation of a DHT DID document.
Expand Down Expand Up @@ -1014,17 +1024,31 @@ export class DidDhtDocument {
case dnsRecordId.startsWith('k'): {
// Get the method ID fragment (id), key type (t), Base64URL-encoded public key (k), and
// optionally, controller (c) from the decoded TXT record data.
const { id, t, k, c } = DidDhtUtils.parseTxtDataToObject(answer.data);
const { id, t, k, c, alg: parsedAlg } = DidDhtUtils.parseTxtDataToObject(answer.data);

// Convert the public key from Base64URL format to a byte array.
const publicKeyBytes = Convert.base64Url(k).toUint8Array();

// Use the key type integer to look up the cryptographic curve name.
const namedCurve = DidDhtRegisteredKeyType[Number(t)];

// TODO: Remove after testing
// Determine the algorithm from the key type or use the initial algorithm if provided.
// const alg = parsedAlg || DidDhtRegisteredKeyType[Number(t)];

// Convert the public key from a byte array to JWK format.
let publicKey = await DidDhtUtils.keyConverter(namedCurve).bytesToPublicKey({ publicKeyBytes });

// Always set the algorithm on did:dht expansion.
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publicKey.alg = parsedAlg || getJoseSignatureAlgorithmFromPublicKey(publicKey);
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Sanity: getJoseSignatureAlgorithmFromPublicKey() does not seem to return Ed25519 that will be expected of vector 3.

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am I using this correctly?

export function getJoseSignatureAlgorithmFromPublicKey(publicKey: Jwk): string {
  const curveToJoseAlgorithm: Record<string, string> = {
    'Ed25519'   : 'EdDSA',
    'P-256'     : 'ES256',
    'P-384'     : 'ES384',
    'P-521'     : 'ES512',
    'secp256k1' : 'ES256K',
  };

  // If the key contains an `alg` property that matches a JOSE registered algorithm identifier,
  // return its value.
  if (publicKey.alg && Object.values(curveToJoseAlgorithm).includes(publicKey.alg)) {
    return publicKey.alg;
  }

  // If the key contains a `crv` property, return the corresponding algorithm.
  if (publicKey.crv && Object.keys(curveToJoseAlgorithm).includes(publicKey.crv)) {
    return curveToJoseAlgorithm[publicKey.crv];
  }

  throw new Error(
    `Unable to determine algorithm based on provided input: alg=${publicKey.alg}, crv=${publicKey.crv}. ` +
    `Supported 'alg' values: ${Object.values(curveToJoseAlgorithm).join(', ')}. ` +
    `Supported 'crv' values: ${Object.keys(curveToJoseAlgorithm).join(', ')}.`
  );
}

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@nitro-neal nitro-neal May 2, 2024

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I think the alg is always there for our jwks, but is that not necessarily the case for outside jwks inside the did dht??

if the alg is always there we can just do

if(parsedAlg) {
   publicKey.alg = parsedAlg
}

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I don't get if(parsedAlg) { publicKey.alg = parsedAlg }, if parsedAlg is always defined, then there is nothing do right? since:

const { id, t, k, c, a: parsedAlg } = DidDhtUtils.parseTxtDataToObject(answer.data);

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parsed alg will not always be defined, but publicKey.alg is always defined


// Determine the Key ID (kid): '0' for the identity key or JWK thumbprint for others. Always set alg on expansion.
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if (id !== '0' && publicKey.kid === undefined) {
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For my understanding: why would kid be defined when id is not 0? May have opportunity to simplify the condition here?

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simplifying to:

          if (id === '0') {
            publicKey.kid = '0';
          } else if (publicKey.kid === undefined) {
            publicKey.kid = await computeJwkThumbprint({ jwk: publicKey });
          }

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the publicKey.kid should be defined, but if it is not, we can recompute it deterministically with computeJwkThumbprint

publicKey.kid = await computeJwkThumbprint({ jwk: publicKey });
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} else if (id === '0') {
publicKey.kid = '0';
}

// Initialize the `verificationMethod` array if it does not already exist.
didDocument.verificationMethod ??= [];

Expand Down Expand Up @@ -1159,7 +1183,11 @@ export class DidDhtDocument {
let methodId = vm.id.split('#').pop()!; // Remove fragment prefix, if any.
idLookup.set(methodId, dnsRecordId);

const publicKey = vm.publicKeyJwk;
const publicKey = vm.publicKeyJwk!;

if(methodId === '0') {
publicKey.kid = '0';
}
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if (!(publicKey?.crv && publicKey.crv in AlgorithmToKeyTypeMap)) {
throw new DidError(DidErrorCode.InvalidPublicKeyType, `Verification method '${vm.id}' contains an unsupported key type: ${publicKey?.crv ?? 'undefined'}`);
Expand All @@ -1168,14 +1196,20 @@ export class DidDhtDocument {
// Use the public key's `crv` property to get the DID DHT key type.
const keyType = DidDhtRegisteredKeyType[publicKey.crv as keyof typeof DidDhtRegisteredKeyType];

let alg;
if(KeyTypeToDefaultAlgorithmMap[keyType] !== getJoseSignatureAlgorithmFromPublicKey(publicKey))
{
alg = getJoseSignatureAlgorithmFromPublicKey(publicKey);
}

// Convert the public key from JWK format to a byte array.
const publicKeyBytes = await DidDhtUtils.keyConverter(publicKey.crv).publicKeyToBytes({ publicKey });

// Convert the public key from a byte array to Base64URL format.
const publicKeyBase64Url = Convert.uint8Array(publicKeyBytes).toBase64Url();

// Define the data for the DNS TXT record.
const txtData = [`id=${methodId}`, `t=${keyType}`, `k=${publicKeyBase64Url}`];
const txtData = [`id=${methodId}`, `t=${keyType}`, `k=${publicKeyBase64Url}`, ...(alg ? [`alg=${alg}`] : [])];
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// Add the controller property, if set to a value other than the Identity Key (DID Subject).
if (vm.controller !== didDocument.id) txtData.push(`c=${vm.controller}`);
Expand Down
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