/**
     * Encrypt using AES-GCM with constant-time operations
     */
    private EncryptionResult encryptWithGCM(byte[] message, byte[] nonce, byte[] associatedData) throws Exception {
        final Cipher cipher = createGCMCipher(true, nonce);
        cipher.updateAAD(associatedData);

        // Use constant-time encryption
        final byte[] encrypted = performConstantTimeEncryption(cipher, message);