I uploaded a zip with source files for MD5 encryption on NSString.
http://cl.ly/1M420J0b1Y2f
If you put the sourcecode in your application, do the correct #import.
You should be able to call
NSString *md5string = [whateverStringToBeEncrypted md5];
Then your new md5string pointer will contain the md5 encrypted version of whateverStringToBeEncrypted.
Please do mind, there are several different MD5 encryptions, in this case 16 & 32 bit..
They are both in there, just comment the right one out (currently configured for 32 bit).