If you need a valid product key for any version of Windows, you must purchase it from an authorized source or use a legally acquired volume license. Using unauthorized keys violates Microsoft’s terms of service and may expose you to security risks from non-genuine software.
While there isn't a single "official" legend specifically for the 64-bit version's key, the story of Windows XP product keys is dominated by the , a catastrophic leak that defined an entire era of software piracy. The Legend of the "FCKGW" Key windows xp professional 64 bit product key