Yesterday the IDPF published on their Website an "informational document" on
Font Embedding for Open Container Format Files. This document describes a font-obfuscation method which is similar to Adobe's, but incompatible. The format of META-INF/encryption.xml means there is no confusion about which method is used, but a single file can't be obfuscated with both methods.
Come on, IDPF -- so Adobe has gone unilateral in extending EPUB in directions they want, but does recommending an incompatible obfuscation method (which no one implements) really help anyone?