From e3bba6a0da3a0de14b11431259cedc503a911ea9 Mon Sep 17 00:00:00 2001
From: Chris Duncan <chris@codecow.com>
Date: Fri, 14 Aug 2026 16:29:17 -0700
Subject: [PATCH] Avoid writing seed to output buffer of derive since the
 private key bytes are discarded by JS caller anyway.

---
 src/assembly/index.ts | 13 +++++--------
 src/lib/nano25519.ts  |  2 +-
 2 files changed, 6 insertions(+), 9 deletions(-)

diff --git a/src/assembly/index.ts b/src/assembly/index.ts
index 51e1b6d..da1d0ee 100644
--- a/src/assembly/index.ts
+++ b/src/assembly/index.ts
@@ -36,8 +36,7 @@ function crypto_derive (sk: StaticArray<u8>, seed: StaticArray<u8>): void {
 	clamp(sk)
 
 	ge_scalarmult_base_tobytes(pk, sk)
-	memory.copy(changetype<usize>(sk), changetype<usize>(seed), PRIVATEKEY_BYTES)
-	memory.copy(changetype<usize>(sk) + 32, changetype<usize>(pk), PUBLICKEY_BYTES)
+	memory.copy(changetype<usize>(sk), changetype<usize>(pk), PUBLICKEY_BYTES)
 }
 
 const crypto_sign_az = new StaticArray<u8>(64)
@@ -137,16 +136,14 @@ export function getMessagePointer (): usize {
 }
 
 /**
- * Derives a Nano public key from a private key and writes it to the static
- * output buffer. This mirrors the functionality of
- * `nacl.sign.keyPair.fromSeed()`, returning both private and public keys as a
- * concatenated `secretKey` property.
+ * Uses a private key to derive a Nano public key which is then written to the
+ * static output buffer.
  */
 export function derive (): void {
-	const sk = changetype<StaticArray<u8>>(OUTPUT_BUFFER)
+	const pk = changetype<StaticArray<u8>>(OUTPUT_BUFFER)
 	const seed = changetype<StaticArray<u8>>(INPUT_BUFFER)
 	memory.fill(OUTPUT_BUFFER, 0, SECRETKEY_BYTES)
-	crypto_derive(sk, seed)
+	crypto_derive(pk, seed)
 	memory.fill(INPUT_BUFFER, 0, PRIVATEKEY_BYTES)
 }
 
diff --git a/src/lib/nano25519.ts b/src/lib/nano25519.ts
index da2def5..ca2fe32 100644
--- a/src/lib/nano25519.ts
+++ b/src/lib/nano25519.ts
@@ -85,7 +85,7 @@ export const nano25519_init = (bytes: number[]): { derive: typeof derive, sign:
 			const outPtr = exports.getOutputPointer()
 			buffer = new DataView(exports.memory.buffer)
 			for (let i = 0; i < 32; i++) {
-				out[i] = buffer.getUint8(outPtr + i + 32)
+				out[i] = buffer.getUint8(outPtr + i)
 			}
 			clear(buffer)
 			if (typeof k === 'string') {
-- 
2.52.0