DCP developer here. DCP track files are MXF. SMPTE ST 377:2004 (MXF) predates SMPTE ST 429-3:2007 (DCP Sound and Picture.) ST 377 is a normative reference of ST 429-3. There is no zip file. There is no central registration for encryption. Each Media Block has a 2k RSA key (usually generated inside the FIPS 140 boundary), and each content distributor has a collection of the respective X.509 certificates.