move low-level DID-related create & decode into separate folder (#120)

Co-authored-by: Trent Larson <trent@trentlarson.com>
Reviewed-on: trent_larson/crowd-funder-for-time-pwa#120
Co-authored-by: trentlarson <trent@trentlarson.com>
Co-committed-by: trentlarson <trent@trentlarson.com>

src/libs/crypto/vc/didPeer.ts

@@ -0,0 +1,96 @@
+import {Buffer} from "buffer/";
+import {decode as cborDecode} from "cbor-x";
+import {bytesToMultibase, multibaseToBytes} from "did-jwt";
+
+import {getWebCrypto} from "@/libs/crypto/vc/passkeyHelpers";
+
+const PEER_DID_PREFIX = "did:peer:";
+const PEER_DID_MULTIBASE_PREFIX = PEER_DID_PREFIX + "0";
+
+/**
+ *
+ *
+ * similar code is in crowd-funder-for-time-pwa libs/crypto/vc/passkeyDidPeer.ts verifyJwtWebCrypto
+ *
+ * @returns {Promise<boolean>}
+ */
+export async function verifyPeerSignature(
+  payloadBytes: Buffer,
+  issuerDid: string,
+  signatureBytes: Uint8Array,
+): Promise<boolean> {
+  const publicKeyBytes = peerDidToPublicKeyBytes(issuerDid);
+
+  const WebCrypto = await getWebCrypto();
+  const verifyAlgorithm = {
+    name: "ECDSA",
+    hash: { name: "SHA-256" },
+  };
+  const publicKeyJwk = cborToKeys(publicKeyBytes).publicKeyJwk;
+  const keyAlgorithm = {
+    name: "ECDSA",
+    namedCurve: publicKeyJwk.crv,
+  };
+  const publicKeyCryptoKey = await WebCrypto.subtle.importKey(
+    "jwk",
+    publicKeyJwk,
+    keyAlgorithm,
+    false,
+    ["verify"],
+  );
+  const verified = await WebCrypto.subtle.verify(
+    verifyAlgorithm,
+    publicKeyCryptoKey,
+    signatureBytes,
+    payloadBytes,
+  );
+  return verified;
+}
+
+export function cborToKeys(publicKeyBytes: Uint8Array) {
+  const jwkObj = cborDecode(publicKeyBytes);
+  if (
+    jwkObj[1] != 2 || // kty "EC"
+    jwkObj[3] != -7 || // alg "ES256"
+    jwkObj[-1] != 1 || // crv "P-256"
+    jwkObj[-2].length != 32 || // x
+    jwkObj[-3].length != 32 // y
+  ) {
+    throw new Error("Unable to extract key.");
+  }
+  const publicKeyJwk = {
+    alg: "ES256",
+    crv: "P-256",
+    kty: "EC",
+    x: arrayToBase64Url(jwkObj[-2]),
+    y: arrayToBase64Url(jwkObj[-3]),
+  };
+  const publicKeyBuffer = Buffer.concat([
+    Buffer.from(jwkObj[-2]),
+    Buffer.from(jwkObj[-3]),
+  ]);
+  return { publicKeyJwk, publicKeyBuffer };
+}
+
+export function toBase64Url(anythingB64: string) {
+  return anythingB64.replace(/\+/g, "-").replace(/\//g, "_").replace(/=+$/, "");
+}
+
+export function arrayToBase64Url(anything: Uint8Array) {
+  return toBase64Url(Buffer.from(anything).toString("base64"));
+}
+
+export function peerDidToPublicKeyBytes(did: string) {
+  return multibaseToBytes(did.substring(PEER_DID_MULTIBASE_PREFIX.length));
+}
+
+export function createPeerDid(publicKeyBytes: Uint8Array) {
+  // https://github.com/decentralized-identity/veramo/blob/next/packages/did-provider-peer/src/peer-did-provider.ts#L67
+  //const provider = new PeerDIDProvider({ defaultKms: LOCAL_KMS_NAME });
+  const methodSpecificId = bytesToMultibase(
+    publicKeyBytes,
+    "base58btc",
+    "p256-pub",
+  );
+  return PEER_DID_MULTIBASE_PREFIX + methodSpecificId;
+}