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

Swift 3:

import Security

func randomBytes(length: Int) -> Data {
    var data = Data(capacity: length)
    data.withUnsafeMutableBytes { (bytes: UnsafeMutablePointer) -> Void in
        let _ = SecRandomCopyBytes(kSecRandomDefault, length, bytes)
    }
    return data
}