Today, I was looking at how to add password protection to an app. The basic design was the user could set a password via the options, then when they relaunched the app, would be asked to re-enter the numeric sequence. If they got it right, the app would proceed as normal otherwise, terminate.
Ultimately, I went with the solution proposed by Jeff LaMarche on his blog. But, many of the other solutions I found via Google appeared to use private APIs (such as addTextFieldWithValue:) which is a sure fire way to get rejected these days.
If you haven’t read the blog, or even better – his book, they are both great. The book offers a very easy introduction to the iPhone SDK using practical examples. It’s a great starting place for developers new to the SDK.