This is a joke, but also everyone is on vacation, so how about a thread where we actually *do* decode this, because Windows license keys aren't actually random. https://twitter.com/SwiftOnSecurity/status/1343583153475231749

License keys use a 24-letter alphabet designed to avoid letters that look like numbers (like 1 and I and L) to make them easier to type. Specifically:

B C D F G H J K M P Q R T V W X Y 2 3 4 6 7 8 9

These are arranged into 5 blocks of 6, with hyphen separators for easier typing

The letters, then, are really just a base-24 encoding of the *actual* license key. In this case, that's the binary sequence:

46 40 4b cc f9 45 ec c0 e1 80 b8 f1 d5 c8 00

Ultimately the license key resolves to a Product ID, and the Product ID is what gets validated. Product IDs are of the form AAAAA-BBB-CCCCCCC-DDDDD

Here, the BBB and CCCCCCC values are derived from the first four bytes of the base-24 decoded value.

To do this, we take the first four bytes: 0x46, 0x40, 0x4b, 0xcc, and interpret them into a 32-bit signed integer (0xcc4b4046), drop the sign bit to get 0x4c4b4046, and shift it left by 1 to get 0x2625a023, which is 640000035 in decimal

We divide that number by 1000000 to get the BBB component, i.e. 640 here. 640 in the BBB column means "volume licensing".

The CCCCCC column also comes from this value, and acts as a check. We compute it as follows:

Take the number we previously had (640000035) and find its remainder modulo 1000000 to get 35

We now need to append a number to this value, such that the sum of all the digits in this number are divisible by 7.

Our remainder so far is 35, and 3+5=8, so we pick the number 6 (since 8+6=14, which is divisible by 7) to get the CCCCC component 356

OK, so what about the AAAAA and DDDDD values in the Product ID? Those come from the OS itself. AAAAA is the "Microsoft Product Code" of the software. Here it'll be 55274, which means "Windows XP Pro OEM"

And the DDDDD is really itself two components. The last three digits are a randomly chosen number, and the first two are the index of the public key that validated the digital signature on the Windows Genuine Advantage check (and will be 23 for this key).

So long story short is the famous pirated license key "FCKGW-RHQQ2-YXRKT-8TG6W-2B7Q8" does actually encode some information! It says "I am a Windows XP Pro OEM volume licensing key", and if you used it to pirate XP, you'd have ended up with Product ID 55274-640-0000356-23XXX.