Update 7/15/17: The encoding is still base24, but the position of the N forms the first character. It now appears to be base 25 with the following alphabet (the newcomer being N): Going by the characters in the KMS client keys, Windows 8 and beyond changed the product key alphabet. The signature over the composite number appears to be a Schnorr signature over a truncated SHA-1 hash of the composite number. Windows XP also includes a file called pidgen.dll. This highly suggests that Windand XP all share the same product key validation algorithm. Looking at a few keys available to me for XP, it appears that the validation of the serial number itself works still the same as in 95 and NT 4.0, too.

Therefore, the decoded product composite number contains:Īt some point, the site IDs became called 'channel IDs' instead. It thus appears reasonable to assume that the format of the site ID was kept and the composite number indeed is the same as the CD key for retail in 95 and NT 4.0. This looks very reminiscent of the Windows 95 OEM key format, except 'OEM' was replaced with '583'. The paper also states that an installation ID for that product key would look something like this: 5503392-00123

The decoded product key (i.e., the raw binary of the key, converted from base 24) contains two parts:Ī digital signature over the composite numberįrom the paper's example, the product key FFFFF-GGGGG-HHHHH-JJJJJ-KKKKK gets decoded (after some rearrangement and a bit shift) to a composite number of 583728439. Īccording to a paper by Fully Licensed GmbH, the base 24 encoding stayed the same. Windows XP follows the same encoding as Windows.

Windows 2000 product key