15.5 Encryption Security Considerations

This section discusses some special security considerations in XML Encryption.

15.5.1 Combining XMLDSIG and XML Encryption

Special considerations apply when you use both authentication and confidentiality together. Refer to Chapter 16 for more details.

15.5.2 Information Revealed

As discussed in Chapter 2, when you share a symmetric key amongst multiple recipients, you can safely use that key only for data intended for all recipients. That is, any recipient not sent the data might intercept the information and decrypt it.

Application designers should not reveal any information in parameters or algorithm identifiers (e.g., in plain text URIs) that weakens the encryption or tends to compromise the plain text.

15.5.3 Care with Algorithms and Expressions

Take care when executing or interpreting algorithms, executable content such as XSLT stylesheets, or even XPath expressions. Such actions can consume unacceptable amounts of time, memory, or other resources, cause errors, or, in the worst case, release viruses or other malware. Some clients may be unable to decrypt even properly encrypted material that has been correctly encoded into XML because of algorithms or other optional capabilities they do not implement, URIs they cannot or will not dereference, insufficient resources, policy, or other reasons.

Stick to the simplest options, preferably those whose implementation is mandatory or at least recommended, to ensure the widest interoperability for your applications.