Question: I am in the process of building an application for the iMac and iPhone. The goal of the application is to encrypt plain text messages, e-mails, passwords, dates, etc. I have done some research and found that 3DES would work great and is very secure. Does anyone know how to implement 3DES in Objective-C for the iPhone or Mac? Any help would be appreciated! Thanks!

Answer: 
Both iOS and OS X have the [`CommonCrypto`](http://developer.apple.com/library/mac/#DOCUMENTATION/Darwin/Reference/ManPages/man3/CCCrypt.3cc.html) library, which provides implementations of AES, 3DES, and DES, among others. Writing your own crypto library is difficult, error prone, and likely to cause bugs. Besides which, if you write your own encryption library, then you have to declare it and go through a U.S. government approval process if you ever plan to put it in the App Store.
It probably doesn't make a lot of sense to try to re-implement DES or any other encryption algorithm in Objective-C when there are well-known versions implemented in C and/or C++. You can simply call any of those from your Objective-C program.