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Because messages are exchanged encapsulated in XML, there are two well defined ways to handle signing of the messages. One is XML Signatures, the other - and somewhat simpler - is Cryptographic Message Syntax - also known as PKCS#7. As one of the objectives is to prevent message tampering, there is no need for the granularity of XML Signatures. Therefore Cryptographic Message Syntax is chosen for signing and optionally encrypting messages. The identity of the signer is embedded in the public certifice certificate