ISO 26430-3:2008提供了一种通用额外影院消息（ETM）格式的规范，该格式用于数字电影系统安全通信中使用的单向通信信道。 ETM规范是一个通用的可扩展标记语言（XML）安全包装器，其中包含特定字段，可以扩展这些字段以承载不同类型的信息，以满足各种应用程序级别的要求。ETM使用W3C XML来表示信息负载。它使用XML加密和签名原语提供安全性。

ISO 26430-3:2008 presents a specification for a generic extra-theater message (ETM) format for use with unidirectional communications channels used in security communications for digital cinema systems. The ETM specification is a generic extensible markup language (XML) security wrapper that includes specific fields which can be extended to carry different kinds of information to meet various application-level requirements. The ETM uses W3C XML to represent the information payload. It provides security using the XML encryption and signature primitives.