There's an entertaining article about one such attack here: http://blog.cryptographyengineering.com/2011/10/attack-of-week-xml-encryption.html http://blog.cryp

There's an entertaining article about one such attack here: http://blog.cryptographyengineering.com/2011/10/attack-of-week-xml-encryption.html http://blog.cryptographyengineering.com/2011/10/attack-of-we... For some mind-boggling reason, the designers of the XML Encryption standard decided to make authentication optional, so an attacker can simply avoid sending an incorrect MAC.