From 7b6378283c03d85d095500c92585095346c92fa8 Mon Sep 17 00:00:00 2001
From: Chris Duncan <chris@zoso.dev>
Date: Sat, 2 Aug 2025 22:40:12 -0700
Subject: [PATCH] Convert index to bytes with buffers instead of string
 manipulation.

---
 src/lib/blake2b-ckd.ts | 13 ++++++-------
 src/lib/blake2b.ts     |  8 ++++----
 2 files changed, 10 insertions(+), 11 deletions(-)

diff --git a/src/lib/blake2b-ckd.ts b/src/lib/blake2b-ckd.ts
index b347a5e..7f75f07 100644
--- a/src/lib/blake2b-ckd.ts
+++ b/src/lib/blake2b-ckd.ts
@@ -2,7 +2,6 @@
 //! SPDX-License-Identifier: GPL-3.0-or-later
 
 import { Blake2b } from '#src/lib/blake2b.js'
-import { hex } from '#src/lib/convert.js'
 
 /**
 * Derives account private keys from a wallet seed using the BLAKE2b hashing
@@ -14,15 +13,15 @@ import { hex } from '#src/lib/convert.js'
 * https://docs.nano.org/integration-guides/the-basics/
 *
 * @param {ArrayBuffer} seed - 32-byte secret seed of the wallet
-* @param {number} index - Account to derive
+* @param {number} index - 4-byte index of account to derive
 * @returns {ArrayBuffer} Private key for the account
 */
 export class Blake2bCkd {
 	static ckd (seed: ArrayBuffer, index: number): ArrayBuffer {
-		return new Blake2b(32)
-			.update(new Uint8Array(seed))
-			.update(hex.toBytes(index.toString(16).padStart(8, '0')))
-			.digest()
-			.buffer
+		const b = new ArrayBuffer(4)
+		new DataView(b).setUint32(0, index, false)
+		const s = new Uint8Array(seed)
+		const i = new Uint8Array(b)
+		return new Blake2b(32).update(s).update(i).digest().buffer
 	}
 }
diff --git a/src/lib/blake2b.ts b/src/lib/blake2b.ts
index 47c1297..319e73b 100644
--- a/src/lib/blake2b.ts
+++ b/src/lib/blake2b.ts
@@ -256,12 +256,12 @@ export class Blake2b {
 		}
 	}
 
-	update (input: Uint8Array<ArrayBuffer>): Blake2b {
+	update (input: Uint8Array): Blake2b {
 		if (input instanceof ArrayBuffer) {
 			input = new Uint8Array(input)
 		}
 		if (!(input instanceof Uint8Array)) {
-			throw new TypeError(`input must be Uint8Array or Buffer`)
+			throw new TypeError('Input must be Uint8Array or Buffer')
 		}
 		this.#blake2bUpdate(input)
 		return this
@@ -272,8 +272,8 @@ export class Blake2b {
 	digest (out: 'binary' | Uint8Array<ArrayBuffer>): Uint8Array<ArrayBuffer>
 	digest (out?: 'binary' | 'hex' | Uint8Array<ArrayBuffer>): string | Uint8Array<ArrayBuffer> {
 		const buf = (!out || out === 'binary' || out === 'hex') ? new Uint8Array(this.#outlen) : out
-		if (!(buf instanceof Uint8Array)) throw new TypeError(`out must be "binary", "hex", Uint8Array, or Buffer`)
-		if (buf.length < this.#outlen) throw new RangeError(`out must have at least outlen bytes of space`)
+		if (!(buf instanceof Uint8Array)) throw new TypeError('out must be "binary", "hex", Uint8Array, or Buffer')
+		if (buf.length < this.#outlen) throw new RangeError('out must have at least outlen bytes of space')
 		this.#blake2bFinal(buf)
 		return (out === 'hex')
 			? Blake2b.#toHex(buf)
-- 
2.47.3