Best way to generate NSData object with random bytes of a specific length?

Question

If I create a new NSData object of a specific size using dataWithBytes:length:, what is the most efficient way to create the input bytes (20 Mb worth) of random characters, pref

Answer 1

void * bytes = malloc(numberOfBytes);
NSData * data = [NSData dataWithBytes:bytes length:numberOfBytes];
free(bytes);

The bytes are not 'random', but will contain garbage values (whatever was on the heap before this was run). The advantage being its fast and the code is concise.