Add deriveSlip21Node

Author: steida

.changeset/small-lights-go.md

@@ -0,0 +1,5 @@
+---
+"@evolu/common": patch
+---
+
+Add deriveSlip21Node

eslint.config.mjs

@@ -94,6 +94,7 @@ export default tseslint.config(
       "@typescript-eslint/no-non-null-assertion": "off",
       "no-console": "error",
       "@typescript-eslint/restrict-template-expressions": "off",
+      "@typescript-eslint/triple-slash-reference": "off",
       "react-hooks/rules-of-hooks": "error",
       "react-hooks/exhaustive-deps": "error",
       "jsdoc/require-jsdoc": "off",

packages/common/src/Crypto.ts

@@ -22,6 +22,7 @@ import {
 } from "./Type.js";
 import { Brand } from "./Brand.js";
 import { assert } from "./Assert.js";
+import { utf8ToBytes } from "./Buffer.js";
 
 /** `Uint8Array` created by {@link createRandomBytes}. */
 export type RandomBytes = Uint8Array & Brand<"RandomBytes">;
@@ -56,25 +57,37 @@ export const mnemonicToMnemonicSeed = (mnemonic: Mnemonic): MnemonicSeed =>
  * https://github.com/satoshilabs/slips/blob/master/slip-0021.md
  */
 export const createSlip21 = (
-  seed: MnemonicSeed,
+  seed: Uint8Array,
   path: ReadonlyArray<string>,
 ): Uint8Array => {
   assert(
     seed.length >= 16 && seed.length <= 64,
     `Unusual SLIP-0021 seed length: ${seed.length} bytes`,
   );
 
-  let m = hmac(sha512, "Symmetric key seed", seed);
+  let m = hmac(sha512, utf8ToBytes("Symmetric key seed"), seed);
   for (const component of path) {
-    const p = new TextEncoder().encode(component);
-    const e = new globalThis.Uint8Array(p.byteLength + 1);
-    e[0] = 0;
-    e.set(p, 1);
-    m = hmac(sha512, m.slice(0, 32), e);
+    m = deriveSlip21Node(component, m);
   }
   return m.slice(32, 64);
 };
 
+/**
+ * Derives a single node in the SLIP-21 hierarchical key derivation.
+ *
+ * @see {@link createSlip21}
+ */
+export const deriveSlip21Node = (
+  component: string,
+  m: Uint8Array,
+): Uint8Array => {
+  const p = utf8ToBytes(component);
+  const e = new globalThis.Uint8Array(p.byteLength + 1);
+  e[0] = 0;
+  e.set(p, 1);
+  return hmac(sha512, m.slice(0, 32), e);
+};
+
 /**
  * Creates a 21-character Base64URL ID (also known as nanoid) from a SLIP-21
  * derived key.