feat: digest multibase utility fn

package.json

@@ -99,6 +99,7 @@
     "zod-to-json-schema": "^3.23.0"
   },
   "dependencies": {
+    "@aws-crypto/sha256-universal": "^5.2.0",
     "@govtechsg/jsonld": "^0.1.0",
     "buffer": "^6.0.3",
     "cross-fetch": "^3.1.5",

src/4.0/computeDigestMultibase.ts

@@ -0,0 +1,20 @@
+import { Sha256 } from "@aws-crypto/sha256-universal";
+import { base58 } from "ethers/lib/utils";
+
+/**
+ * Computes a SHA-256 digest of the provided data and encodes it in Base58 with a 'z' prefix,
+ * conforming to the Multibase encoding standard. This function is intended for generating
+ * a multibase-encoded multihash, specifically using SHA-2 with 256-bits of output.
+ * The multibase value is fixed as 'z' to match the specifications.
+ *
+ * @param {ArrayBuffer|string} data - The data to hash. This can be either a string or an ArrayBuffer.
+ * @returns {Promise<string>} A promise that resolves to the Base58 encoded SHA-256 hash of the input data,
+ *                            prefixed with 'z' as per the Multibase specification.
+ */
+export async function computeDigestMultibase(data: ArrayBuffer | string): Promise<string> {
+  const sha256 = new Sha256();
+  sha256.update(data);
+  const sha256Digest = await sha256.digest();
+  // manually prefix with 'z' as per https://w3c-ccg.github.io/multibase/#mh-registry
+  return `z${base58.encode(sha256Digest)}`;
+}

src/4.0/exports/utils.ts

@@ -4,3 +4,4 @@ export {
   isV4WrappedDocument as isWrappedDocument,
   isV4SignedWrappedDocument as isSignedWrappedDocument,
 } from "../types";
+export { computeDigestMultibase } from "../computeDigestMultibase";