reworking the lowercase to use an appropriate format as opposed to lowercaseString

CryptoSwift/NSDataExtension.swift

@@ -91,9 +91,9 @@ extension NSData {
         
         var s:String = "";
         for byte in bytesArray {
-            s = s + String(format:"%02X", byte)
+            s = s + String(format:"%02x", byte)
         }
-        return s;
+        return s
     }
     
     public func arrayOfBytes() -> [UInt8] {