From: Chris Duncan <chris@codecow.com>
Date: Fri, 15 May 2026 08:05:42 +0000 (-0700)
Subject: Extract child key algorithm steps 2-6 to its own function.
X-Git-Url: https://git.codecow.com/?a=commitdiff_plain;h=f957b11014ad62a6c1b204f686b4c8cc46c5331d;p=libnemo.git

Extract child key algorithm steps 2-6 to its own function.
---

diff --git a/src/lib/crypto/bip44.ts b/src/lib/crypto/bip44.ts
index 922b7d1..040bdc6 100644
--- a/src/lib/crypto/bip44.ts
+++ b/src/lib/crypto/bip44.ts
@@ -103,24 +103,26 @@ function CKDpriv (curve: Curve, { privateKey, chainCode }: ExtendedKey, index?:
 	const key = chainCode
 	const data = t.buffer
 	return hmac(key, data)
-		.then(I => {
-			const IL = I.slice(0, I.byteLength / 2)
-			const IR = I.slice(I.byteLength / 2)
-			if (curve === 'ed25519 seed') {
-				return ({ privateKey: IL, chainCode: IR })
-			} else {
-				const ILparsed = parse256(new Uint8Array(IL))
-				if (ILparsed >= Point.CURVE().n) {
-					throw new Error('Invalid child key is greater than the order of the curve')
-				}
-				const pkParsed = parse256(pk)
-				const childKey = (ILparsed + pkParsed) % Point.CURVE().n
-				if (childKey === 0n) {
-					throw new Error('Invalid child key is zero')
-				}
-				return ({ privateKey: ser256(childKey).buffer, chainCode: IR })
-			}
-		})
+		.then(I => childKey(curve, pk, I))
+}
+
+function childKey (curve: Curve, pk: Bytes, I: ArrayBuffer): ExtendedKey {
+	const IL = I.slice(0, I.byteLength / 2)
+	const IR = I.slice(I.byteLength / 2)
+	if (curve === 'ed25519 seed') {
+		return ({ privateKey: IL, chainCode: IR })
+	} else {
+		const ILparsed = parse256(new Uint8Array(IL))
+		if (ILparsed >= Point.CURVE().n) {
+			throw new Error('Invalid child key is greater than the order of the curve')
+		}
+		const pkParsed = parse256(pk)
+		const childKey = (ILparsed + pkParsed) % Point.CURVE().n
+		if (childKey === 0n) {
+			throw new Error('Invalid child key is zero')
+		}
+		return ({ privateKey: ser256(childKey).buffer, chainCode: IR })
+	}
 }
 
 function ser32 (integer: number): Bytes {