iOS7 app backward compatible with iOS5 regarding unique identifier

Question

My app is compatible with iOS5 and iOS6. Until now I had no problem using:

NSString DeviceID = [[UIDevice currentDevice] uniqueIdentifier];

Answer 1

Why just not to use CFUUIDRef and be independent with iOS verion?

CFUUIDRef uuidRef = CFUUIDCreate(kCFAllocatorDefault);

self.uuidString = (NSString *)CFUUIDCreateString(NULL,uuidRef);

CFRelease(uuidRef);

And of course remember calculated uuidString in the Keychain(in case of application removal)?

Here is written how to use keychain