I am new to the xcode and also in MAC envronment. I want to know what are the API or methods used for Digital Signing in objective-c using xcode 3.2.5.Xcode 3.2.5? Really?That version of Xcode is very old. What version of OS X are you running it on?With regards signing, there's a specific issue at play. IIRC Xcode 3.2 is for Mac OS X 10.6, and the API you want to use (SecSignTransformCreate) was introduced in OS X 10.7. If you really are stuck on 10.6 then you'll have to use the much older CDSA APIs. These are long-since deprecated, so there's not a lot of information about how to use them. Specifically, I can't help you with them because I never got around to learning them myself. Moreover, I can't recommend that you write new code that targets these APIs because, well, they're deprecated. If there's any chance you can upgrade to OS X 10.7 and Xcode 4.x, the situation will be a lot clearer. Here you'll