* Decrypt a message using the session's encryption context
     *
     * @param encryptedMessage the encrypted message with transform header
     * @return decrypted message
     * @throws CIFSException if decryption fails or encryption is not enabled
     */
    public byte[] decryptMessage(byte[] encryptedMessage) throws CIFSException {
        if (this.encryptionContext == null) {

        } else {
            throw new SmbUnsupportedOperationException("SMB3 required for encryption, negotiated: " + dialect);
        }

        try {
            // Derive encryption and decryption keys using SMB3 KDF
            final int dialectInt = dialect.getDialect();
            final byte[] encryptionKey = Smb3KeyDerivation.deriveEncryptionKey(dialectInt, sessionKey, preauthHash);