fix: memory zeroing for shared secrets and npub input rejection

Zero shared secret buffers after AES key import in encrypt/decrypt.
Zero private key bytes after public key derivation in generateKeyPair.
Reject npub-prefixed inputs in getPublicKeyHex with guidance to use nip19.decode().

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: vveerrgg

src/crypto.ts

@@ -151,6 +151,7 @@ export function getSchnorrPublicKey(privateKeyBytes: Uint8Array): Uint8Array {
 export async function generateKeyPair(): Promise<KeyPair> {
   const privateKeyBytes = randomBytes(32);
   const privateKey = bytesToHex(privateKeyBytes);
+  privateKeyBytes.fill(0); // zero source material
   const publicKey = await getPublicKey(privateKey);
 
   return {
@@ -298,6 +299,10 @@ export async function encrypt(
       ['encrypt']
     ));
 
+    // Zero shared secret material now that AES key is imported
+    sharedX.fill(0);
+    sharedPoint.fill(0);
+
     // Encrypt the message
     const data = new TextEncoder().encode(message);
     const encrypted = await customCrypto.getSubtle().then((subtle) => subtle.encrypt(
@@ -355,6 +360,10 @@ export async function decrypt(
       ['decrypt']
     ));
 
+    // Zero shared secret material now that AES key is imported
+    sharedX.fill(0);
+    sharedPoint.fill(0);
+
     const decrypted = await customCrypto.getSubtle().then((subtle) => subtle.decrypt(
       { name: 'AES-CBC', iv },
       key,

src/nips/nip-04.ts

@@ -117,6 +117,10 @@ export async function encryptMessage(
       ['encrypt']
     );
 
+    // Zero shared secret material now that AES key is imported
+    sharedX.fill(0);
+    sharedPoint.fill(0);
+
     // Generate IV and encrypt
     const iv = new Uint8Array(16);
     await cryptoImpl.getRandomValues(iv);
@@ -179,6 +183,10 @@ export async function decryptMessage(
       ['decrypt']
     );
 
+    // Zero shared secret material now that AES key is imported
+    sharedX.fill(0);
+    sharedPoint.fill(0);
+
     // Parse NIP-04 standard format: base64(ciphertext) + "?iv=" + base64(iv)
     // Also support legacy hex format (iv + ciphertext concatenated) as fallback
     let iv: Uint8Array;

src/utils/validation.ts

@@ -74,7 +74,10 @@ export function validateEvent(event: NostrEvent): ValidationResult {
  * @returns Hex representation of the public key
  */
 export function getPublicKeyHex(pubkey: string): string {
-  return pubkey.startsWith('npub1') ? pubkey.slice(5) : pubkey;
+  if (pubkey.startsWith('npub1')) {
+    throw new Error('npub inputs require bech32 decoding — use nip19.decode() instead');
+  }
+  return pubkey;
 }
 
 /**