This section provides four examples of XML digital signatures, starting with simple cases and working toward more complex cases. Two of the examples are protocol oriented, and two are form/paper oriented.
Assume you want to efficiently secure protocol messages between two parties. One technique would be to use efficient shared secret key message authentication, like that shown in Example 10-6. In this example, the Data element in a protocol message needs to be authenticated. Because we assume that it is an established connection for a simple protocol, the sender and receiver have already agreed on a key, and thus no KeyInfo is present.