05/18 Enhanced codes and functionalities 4

app/static/js/sharing.js

@@ -151,6 +151,38 @@ const SharingCrypto = (() => {
     return JSON.parse(new TextDecoder().decode(plaintext));
   }
 
+  /**
+   * Encrypt a display name string with the ECDH shared key.
+   * Uses the same AES-256-GCM primitive as encryptForShare but operates on
+   * a plain string rather than a JSON-serialised object.
+   */
+  async function encryptName(sharedKey, name) {
+    const iv = window.crypto.getRandomValues(new Uint8Array(12));
+    const plaintext = new TextEncoder().encode(name);
+    const ciphertext = await subtle.encrypt({ name: 'AES-GCM', iv }, sharedKey, plaintext);
+    return {
+      enc_name: bytesToBase64(new Uint8Array(ciphertext)),
+      iv_name: bytesToBase64(iv),
+    };
+  }
+
+  /**
+   * Decrypt an encrypted display name.
+   * Returns null on failure (e.g. legacy share with no enc_name).
+   */
+  async function decryptName(sharedKey, enc_name, iv_name) {
+    try {
+      const plaintext = await subtle.decrypt(
+        { name: 'AES-GCM', iv: base64ToBytes(iv_name) },
+        sharedKey,
+        base64ToBytes(enc_name),
+      );
+      return new TextDecoder().decode(plaintext);
+    } catch {
+      return null;
+    }
+  }
+
   // ── Public API ────────────────────────────────────────────────────────────
 
   return {
@@ -162,6 +194,8 @@ const SharingCrypto = (() => {
     deriveSharedKey,
     encryptForShare,
     decryptShare,
+    encryptName,
+    decryptName,
   };
 })();