From 908bde8f2f7cfc79c5d6183f7ab7e38f1313937a Mon Sep 17 00:00:00 2001
From: Chris Duncan <chris@codecow.com>
Date: Thu, 14 May 2026 13:32:57 -0700
Subject: [PATCH] Reuse text encoder to avoid initializing on every call.
 Consolidate redundant assignments in CKDpriv. Alias byte arrayts for
 legibility. Pass buffers to HMAC.

---
 src/lib/crypto/bip44.ts | 27 ++++++++++++++-------------
 1 file changed, 14 insertions(+), 13 deletions(-)

diff --git a/src/lib/crypto/bip44.ts b/src/lib/crypto/bip44.ts
index 135bae7..922b7d1 100644
--- a/src/lib/crypto/bip44.ts
+++ b/src/lib/crypto/bip44.ts
@@ -3,6 +3,7 @@
 
 import { Point, getPublicKey as secp256k1_getPublicKey } from '@noble/secp256k1'
 
+type Bytes = Uint8Array<ArrayBuffer>
 type Curve = 'Bitcoin seed' | 'ed25519 seed'
 type ExtendedKey = {
 	privateKey: ArrayBuffer
@@ -11,6 +12,7 @@ type ExtendedKey = {
 }
 const BIP44_PURPOSE: 44 = 44
 const HARDENED_OFFSET: 0x80000000 = 0x80000000
+const ENCODER: TextEncoder = new TextEncoder()
 
 /**
  * Derives a private child key for a coin by following the specified BIP-32 and
@@ -74,8 +76,8 @@ function ckd (curve: Curve, seed: ArrayBuffer, coin: number, account: number, ch
 }
 
 function slip10 (curve: string, S: ArrayBuffer): Promise<ExtendedKey> {
-	const key = new Uint8Array(new TextEncoder().encode(curve))
-	const data = new Uint8Array(S)
+	const key = ENCODER.encode(curve).buffer
+	const data = S
 	return hmac(key, data)
 		.then(I => {
 			const IL = I.slice(0, I.byteLength / 2)
@@ -89,18 +91,17 @@ function CKDpriv (curve: Curve, { privateKey, chainCode }: ExtendedKey, index?:
 		return Promise.resolve({ privateKey, chainCode })
 	}
 	const pk = new Uint8Array(privateKey)
-	const key = new Uint8Array(chainCode)
-	const data = new Uint8Array(37)
+	const t = new Uint8Array(37)
 	if (index >= HARDENED_OFFSET) {
-		data.set([0])
-		data.set(pk, 1)
-		data.set(ser32(index), 33)
+		t.set(pk, 1)
 	} else if (curve === 'ed25519 seed') {
 		throw new RangeError('Only hardened child keys are supported for ed25519')
 	} else {
-		data.set(secp256k1_getPublicKey(pk))
-		data.set(ser32(index), 33)
+		t.set(secp256k1_getPublicKey(pk))
 	}
+	t.set(ser32(index), 33)
+	const key = chainCode
+	const data = t.buffer
 	return hmac(key, data)
 		.then(I => {
 			const IL = I.slice(0, I.byteLength / 2)
@@ -122,13 +123,13 @@ function CKDpriv (curve: Curve, { privateKey, chainCode }: ExtendedKey, index?:
 		})
 }
 
-function ser32 (integer: number): Uint8Array<ArrayBuffer> {
+function ser32 (integer: number): Bytes {
 	const view = new DataView(new ArrayBuffer(4))
 	view.setUint32(0, integer, false)
 	return new Uint8Array(view.buffer)
 }
 
-function ser256 (integer: bigint): Uint8Array<ArrayBuffer> {
+function ser256 (integer: bigint): Bytes {
 	let bytes = new Uint8Array(32)
 	for (let i = bytes.byteLength - 1; i >= 0; i--) {
 		bytes[i] = Number(integer & 0xffn)
@@ -137,7 +138,7 @@ function ser256 (integer: bigint): Uint8Array<ArrayBuffer> {
 	return bytes
 }
 
-function parse256 (integer: Uint8Array<ArrayBuffer>): bigint {
+function parse256 (integer: Bytes): bigint {
 	let result = 0n
 	for (let i = 0; i < integer.byteLength; i++) {
 		result = (result << 8n) | BigInt(integer[i])
@@ -145,7 +146,7 @@ function parse256 (integer: Uint8Array<ArrayBuffer>): bigint {
 	return result
 }
 
-function hmac (key: Uint8Array<ArrayBuffer>, data: Uint8Array<ArrayBuffer>): Promise<ArrayBuffer> {
+function hmac (key: ArrayBuffer, data: ArrayBuffer): Promise<ArrayBuffer> {
 	return crypto.subtle
 		.importKey('raw', key, { name: 'HMAC', hash: 'SHA-512' }, false, ['sign'])
 		.then(pk => crypto.subtle.sign('HMAC', pk, data))
-- 
2.47.3