An article that recently made the rounds, though it was written back in September, is called Apple’s Idioten Vektor. It’s a discussion of how the
CCCrypt() function in Apple’s CommonCrypto library, when used in its default cipher block chaining mode, treats the IV (Initialization Vector) parameter as optional. If you don’t supply an IV, it provides its own IV of
Professional Cocoa Application Security also covers CommonCrypto, CBC mode, and the Initialization Vector. Pages 79-88 discuss block encryption. The section includes sample code for both one-shot and staged use of the API. It explains how to set the IV using a random number generator, and why this should be done. Mercifully when the author of the above blog post reviewed the code in my book section, he decided I was doing it correctly.
So both publications cover the same content. There’s a clear difference in presentation technique, though. I realise that the blog post is categorised as a “rant” by the author, and that I’m about to be the pot that calls the kettle black. However, I do not believe that the attitude taken in the post—I won’t describe it, you can read it—is constructive. Calling people out is not cool, helping them get things correct is. Laughing at the “fail” is not something that endears people to us, and let’s face it, security people could definitely be more endearing. We have a difficult challenge: we ask developers to do more work to bring their products to market, to spend more money on engineering (and often consultants), in return for potentially protecting some unquantified future lost revenue and customer hardship.
Yes there is a large technical component in doing that stuff, but solving the above challenge also depends very strongly on relationship management. Security experts need to demonstrate that we’re all on the same side; that we want to work with the rest of the software industry to help make better software. Again, a challenge arises: a lot of the help provided by security engineers comes in the form of pointing out mistakes. But we shouldn’t be self promoting douchebags about it. Perhaps we’re going about it wrong. I always strive to help the developers I work with by identifying and discussing the potential mistakes before they happen. Then there’s less friction: “we’re going to do this right” is a much more palatable story than “you did this wrong”.
On the other hand, the Idioten Vektor approach generated a load of discussion and coverage, while only a couple of thousand people ever read Professional Cocoa Application Security. So there’s clearly something in the sensationalist approach too. Perhaps it’s me that doesn’t get it.
Note that the book was written while iPhone OS 3 was the current version, which is why the file protection options are not discussed. If I were covering the same topic today I would recommend eschewing CCCrypto for all but the most specialised of purposes, and would suggest setting an appropriate file protection level instead. The book also didn’t put encryption into the broader context of cryptographic protocols; a mistake I have since rectified.