Many manufacturers obfuscate their RAW data, including Canon.

Posted Apr 2, 2007 21:33 UTC (Mon) by pizza (subscriber, #46)
In reply to: Working with raw images on Linux by vondo
Parent article: Working with raw images on Linux

To quote Dave Coffin (of dcraw fame)"

A firestorm of controversy recently erupted when Thomas Knoll of Adobe accused Nikon of encrypting the white balance data in the D2X and D2Hs cameras, thus preventing Adobe from fully supporting these cameras.
I cracked this encryption on April 15, and updated dcraw.c and parse.c on April 17. So "dcraw -w" now works correctly with all Nikon cameras.
This is not a new problem. Phase One, Sony, Foveon, and Canon all apply some form of encryption to their RAW files. Dcraw decodes them all -- you can easily find decryption code by searching for the ^ operator.
Compression is not encryption. Phase One and Sony do encryption only. Kodak does compression only. Canon, Nikon, and Foveon compress the image data and encrypt some of the metadata.