feat: add deriveChildKey function

src/index.ts

@@ -9,4 +9,5 @@ export * from "./stringifyJSON.js";
 export * from "./types.js";
 export * from "./cid.js";
 export * from "./encoding.js";
+export * from "./keys.js";
 export { ed25519, sha512 };

src/keys.ts

@@ -0,0 +1,11 @@
+import { blake3 } from "@noble/hashes/blake3";
+import { concatBytes } from "@noble/hashes/utils";
+
+export function deriveChildKey(
+  parentKey: Uint8Array,
+  tweak: string,
+): Uint8Array {
+  const tweakHash = blake3(tweak);
+
+  return blake3(concatBytes(parentKey, tweakHash));
+}