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Inside Windows Product Activation
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Inside Windows Product Activation | |
A Fully Licensed Paper | |
July 2001 | |
Fully Licensed GmbH, Rudower Chaussee 29, 12489 Berlin, Germany | |
http://www.licenturion.com | |
>> INTRODUCTION | |
The current public discussion of Windows Product Activation (WPA) is | |
characterized by uncertainty and speculation. In this paper we supply | |
the technical details of WPA - as implemented in Windows XP - that | |
Microsoft should have published long ago. | |
While we strongly believe that every software vendor has the right to | |
enforce the licensing terms governing the use of a piece of licensed | |
software by technical means, we also do believe that each individual | |
has the right to detailed knowledge about the full implications of the | |
employed means and possible limitations imposed by it on software | |
usage. | |
In this paper we answer what we think are currently the two most | |
important open questions related to Windows Product Activation. | |
* Exactly what information is transmitted during activation? | |
* How do hardware modifications affect an already activated | |
installation of Windows XP? | |
Our answers to these questions are based on Windows XP Release | |
Candidate 1 (build 2505). Later builds as well as the final version of | |
Windows XP might differ from build 2505, e.g. in the employed | |
cryptographic keys or the layout of some of the data | |
structures. | |
However, beyond such minor modifications we expect Microsoft to cling | |
to the general architecture of their activation mechanism. Thus, we | |
are convinced that the answers provided by this paper will still be | |
useful when the final version of Windows XP ships. | |
This paper supplies in-depth technical information about the inner | |
workings of WPA. Still, the discussion is a little vague at some | |
points in order not to facilitate the task of an attacker attempting | |
to circumvent the license enforcement supplied by the activation | |
mechanism. | |
XPDec, a command line utility suitable for verifying the presented | |
information, can be obtained from http://www.licenturion.com/xp/. It | |
implements the algorithms presented in this paper. Reading its source | |
code, which is available from the same location, is highly | |
recommended. | |
We have removed an important cryptographic key from the XPDec source | |
code. Recompiling the source code will thus fail to produce a working | |
executable. The XPDec executable on our website, however, contains | |
this key and is fully functional. | |
So, download the source code to learn about the inner workings of WPA, | |
but obtain the executable to experiment with your installation of | |
Windows XP. | |
We expect the reader to be familiar with the general procedure of | |
Windows Product Activation. | |
>> INSIDE THE INSTALLATION ID | |
We focused our research on product activation via telephone. We did | |
so, because we expected this variant of activation to be the most | |
straight-forward to analyze. | |
The first step in activating Windows XP via telephone is supplying the | |
call-center agent with the Installation ID displayed by msoobe.exe, | |
the application that guides a user through the activation process. The | |
Installation ID is a number consisting of 50 decimal digits that are | |
divided into groups of six digits each, as in | |
002666-077894-484890-114573-XXXXXX-XXXXXX-XXXXXX-XXXXXX-XX | |
In this authentic Installation ID we have substituted digits that we | |
prefer not to disclose by 'X' characters. | |
If msoobe.exe is invoked more than once, it provides a different | |
Installation ID each time. | |
In return, the call-center agent provides a Confirmation ID matching | |
the given Installation ID. Entering the Confirmation ID completes the | |
activation process. | |
Since the Installation ID is the only piece of information revealed | |
during activation, the above question concerning the information | |
transmitted during the activation process is equivalent to the | |
question | |
'How is the Installation ID generated?' | |
To find an answer to this question, we trace back each digit of the | |
Installation ID to its origins. | |
>>> Check digits | |
The rightmost digit in each of the groups is a check digit to guard | |
against simple errors such as the call center agent's mistyping of one | |
of the digits read to him or her. The value of the check digit is | |
calculated by adding the other five digits in the group, adding the | |
digits at even positions a second time, and dividing the sum by | |
seven. The remainder of the division is the value of the check | |
digit. In the above example the check digit for the first group (6) is | |
calculated as follows. | |
1 | 2 | 3 | 4 | 5 <- position | |
---+---+---+---+--- | |
0 | 0 | 2 | 6 | 6 <- digits | |
0 + 0 + 2 + 6 + 6 = 14 (step 1: add all digits) | |
0 + 6 + 14 = 20 (step 2: add even digits again) | |
step 3: division | |
20 / 7 = 2, remainder is 20 - (2 * 7) = 6 | |
=> check digit is 6 | |
Adding the even digits twice is probably intended to guard against the | |
relatively frequent error of accidentally swapping two digits while | |
typing, as in 00626 vs. 00266, which yield different check digits. | |
>>> Decoding | |
Removing the check digits results in a 41-digit decimal number. A | |
decimal number of this length roughly corresponds to a 136-bit binary | |
number. In fact, the 41-digit number is just the decimal encoding of | |
such a 136-bit multi-precision integer, which is stored in little | |
endian byte order as a byte array. Hence, the above Installation ID | |
can also be represented as a sequence of 17 bytes as in | |
0xXX 0xXX 0xXX 0xXX 0xXX 0xXX 0xXX 0xXX | |
0x94 0xAA 0x46 0xD6 0x0F 0xBD 0x2C 0xC8 | |
0x00 | |
In this representation of the above Installation ID 'X' characters | |
again substitute the digits that we prefer not to disclose. The '0x' | |
prefix denotes hex notation throughout this paper. | |
>>> Decryption | |
When decoding arbitrary Installation IDs it can be noticed that the | |
most significant byte always seems to be 0x00 or 0x01, whereas the | |
other bytes look random. The reason for this is that the lower 16 | |
bytes of the Installation ID are encrypted, whereas the most | |
significant byte is kept in plaintext. | |
The cryptographic algorithm employed to encrypt the Installation ID is | |
a proprietary four-round Feistel cipher. Since the block of input | |
bytes passed to a Feistel cipher is divided into two blocks of equal | |
size, this class of ciphers is typically applied to input blocks | |
consisting of an even number of bytes - in this case the lower 16 of | |
the 17 input bytes. The round function of the cipher is the SHA-1 | |
message digest algorithm keyed with a four-byte sequence. | |
Let + denote the concatenation of two byte sequences, ^ the XOR | |
operation, L and R the left and right eight-byte input half for one | |
round, L' and R' the output halves of said round, and First-8() a | |
function that returns the first eight bytes of an SHA-1 message | |
digest. Then one round of decryption looks as follows. | |
L' = R ^ First-8(SHA-1(L + Key)) | |
R' = L | |
The result of the decryption is 16 bytes of plaintext, which are - | |
together with the 17th unencrypted byte - from now on interpreted as | |
four double words in little endian byte order followed by a single | |
byte as in | |
name | size | offset | |
-----+-------------+------- | |
H1 | double word | 0 | |
H2 | double word | 4 | |
P1 | double word | 8 | |
P2 | double word | 12 | |
P3 | byte | 16 | |
H1 and H2 specify the hardware configuration that the Installation ID | |
is linked to. P1 and P2 as well as the remaining byte P3 contain the | |
Product ID associated with the Installation ID. | |
>>> Product ID | |
The Product ID consists of five groups of decimal digits, as in | |
AAAAA-BBB-CCCCCCC-DDEEE | |
If you search your registry for a value named 'ProductID', you will | |
discover the ID that applies to your installation. The 'About' window | |
of Internet Explorer should also yield your Product ID. | |
>>>> Decoding | |
The mapping between the Product ID in decimal representation and its | |
binary encoding in the double words P1 and P2 and the byte P3 is | |
summarized in the following table. | |
digits | length | encoding | |
--------+---------+--------------------------------------- | |
AAAAA | 17 bits | bit 0 to bit 16 of P1 | |
BBB | 10 bits | bit 17 to bit 26 of P1 | |
CCCCCCC | 28 bits | bit 27 to bit 31 of P1 (lower 5 bits) | |
| | bit 0 to bit 22 of P2 (upper 23 bits) | |
DDEEE | 17 bits | bit 23 to bit 31 of P2 (lower 9 bits) | |
| | bit 0 to bit 7 of P3 (upper 8 bits) | |
The meaning of each of the five groups of digits is documented in the | |
next table. | |
digits | meaning | |
--------+------------------------------------------------- | |
AAAAA | apparently always 55034 (in Windows XP RC1) | |
BBB | most significant three digits of Raw Product Key | |
| (see below) | |
CCCCCCC | least significant six digits of Raw Product Key | |
| plus check digit (see below) | |
DD | index of the public key used to verify the | |
| Product Key (see below) | |
EEE | random value | |
As can be seen, the (Raw) Product Key plays an important role in | |
generating the Product ID. | |
>>>> Product Key | |
The Raw Product Key is buried inside the Product Key that is printed | |
on the sticker distributed with each Windows XP CD. It consists of | |
five alphanumeric strings separated by '-' characters, where each | |
string is composed of five characters, as in | |
FFFFF-GGGGG-HHHHH-JJJJJ-KKKKK | |
Each character is one of the following 24 letters and digits: | |
B C D F G H J K M P Q R T V W X Y 2 3 4 6 7 8 9 | |
Very similar to the decimal encoding of the Installation ID the 25 | |
characters of the Product Key form a base-24 encoding of the binary | |
representation of the Product Key. Decoding the Product Key yields a | |
multi-precision integer of roughly 115 bits, which is stored - again | |
in little endian byte order - in an array of 15 bytes. Decoding the | |
above Product Key results in the following byte sequence. | |
0x6F 0xFA 0x95 0x45 0xFC 0x75 0xB5 0x52 | |
0xBB 0xEF 0xB1 0x17 0xDA 0xCD 0x00 | |
Of these 15 bytes the least significant four bytes contain the Raw | |
Product Key in little endian byte order. The least significant bit is | |
removed by shifting this 32-bit value (0x4595FA6F - remember the | |
little endian byte order) to the left by one bit position, resulting | |
in a Raw Product Key of 0x22CAFD37, or | |
583728439 | |
in decimal notation. | |
The eleven remaining bytes form a digital signature, allowing | |
verification of the authenticity of the Product Key by means of a | |
hard-coded public key. | |
>>>> Product Key -> Product ID | |
The three most significant digits, i.e. 583, of the Raw Product Key's | |
nine-digit decimal representation directly map to the BBB component of | |
the Product ID described above. | |
To obtain the CCCCCCC component, a check digit is appended to the | |
remaining six digits 728439. The check digit is chosen such that the | |
sum of all digits - including the check digit - is divisible by | |
seven. In the given case, the sum of the six digits is | |
7 + 2 + 8 + 4 + 3 + 9 = 33 | |
which results in a check digit of 2, since | |
7 + 2 + 8 + 4 + 3 + 9 + 2 = 33 + 2 = 35 | |
which is divisible by seven. The CCCCCCC component of the Product ID | |
is therefore 7284392. | |
For verifying a Product Key, more than one public key is available. If | |
verification with the first public key fails, the second is tried, | |
etc. The DD component of the Product ID specifies which of the public | |
keys in this sequence was successfully used to verify the Product Key. | |
This mechanism might be intended to support several different parties | |
generating valid Product Keys with different individual private keys. | |
However, the different private keys might also represent different | |
versions of a product. A Product Key for the 'professional' release | |
could then be signed with a different key than a Product Key for the | |
'server' release. The DD component would then represent the product | |
version. | |
Finally, a valid Product ID derived from our example Product Key might | |
be | |
55034-583-7284392-00123 | |
which indicates that the first public key (DD = index = 0) matched and | |
123 was chosen as the random number EEE. | |
The randomly selected EEE component is the reason for msoobe.exe | |
presenting a different Installation ID at each invocation. Because of | |
the applied encryption this small change results in a completely | |
different Installation ID. | |
So, the Product ID transmitted during activation will most probably | |
differ in the last three digits from your Product ID as displayed by | |
Internet Explorer or as stored in the registry. | |
>>> Hardware Information | |
As discussed above, the hardware configuration linked to the | |
Installation ID is represented by the two double words H1 and H2. | |
>>>> Bit-fields | |
For this purpose, the double words are divided into twelve | |
bit-fields. The relationship between the computer hardware and the | |
bit-fields is given in the following table. | |
double word | offset | length | bit-field value based on | |
------------+--------+--------+---------------------------- | |
H1 | 0 | 10 | volume serial number string | |
| | | of system volume | |
H1 | 10 | 10 | network adapter MAC address | |
| | | string | |
H1 | 20 | 7 | CD-ROM drive hardware | |
| | | identification string | |
H1 | 27 | 5 | graphics adapter hardware | |
| | | identification string | |
H2 | 0 | 3 | unused, set to 001 | |
H2 | 3 | 6 | CPU serial number string | |
H2 | 9 | 7 | harddrive hardware | |
| | | identification string | |
H2 | 16 | 5 | SCSI host adapter hardware | |
| | | identification string | |
H2 | 21 | 4 | IDE controller hardware | |
| | | identification string | |
H2 | 25 | 3 | processor model string | |
H2 | 28 | 3 | RAM size | |
H2 | 31 | 1 | 1 = dockable | |
| | | 0 = not dockable | |
Bit 31 of H2 specifies, whether the bit-fields represent a notebook | |
computer that supports a docking station. If docking is possible, the | |
activation mechanism will be more tolerant with respect to future | |
hardware modifications. Here, the idea is that plugging a notebook | |
into its docking station possibly results in changes to its hardware | |
configuration, e.g. a SCSI host adapter built into the docking station | |
may become available. | |
Bits 2 through 0 of H2 are unused and always set to 001. | |
If the hardware component corresponding to one of the remaining ten | |
bit-fields is present, the respective bit-field contains a non-zero | |
value describing the component. A value of zero marks the hardware | |
component as not present. | |
All hardware components are identified by a hardware identification | |
string obtained from the registry. Hashing this string provides the | |
value for the corresponding bit-field. | |
>>>> Hashing | |
The hash result is obtained by feeding the hardware identification | |
string into the MD5 message digest algorithm and picking the number of | |
bits required for a bit-field from predetermined locations in the | |
resulting message digest. Different predetermined locations are used | |
for different bit-fields. In addition, a hash result of zero is | |
avoided by calculating | |
Hash = (Hash % BitFieldMax) + 1 | |
where BitFieldMax is the maximal value that may be stored in the | |
bit-field in question, e.g. 1023 for a 10-bit bit-field, and 'x % y' | |
denotes the remainder of the division of x by y. This results in | |
values between 1 and BitFieldMax. The obtained value is then stored in | |
the respective bit-field. | |
>>>> RAM bit-field | |
The bit-field related to the amount of RAM available to the operating | |
system is calculated differently. The seven valid values specify the | |
approximate amount of available RAM as documented in the following | |
table. | |
value | amount of RAM available | |
------+--------------------------- | |
0 | (bit-field unused) | |
1 | below 32 MB | |
2 | between 32 MB and 63 MB | |
3 | between 64 MB and 127 MB | |
4 | between 128 MB and 255 MB | |
5 | between 256 MB and 511 MB | |
6 | between 512 MB and 1023 MB | |
7 | above 1023 MB | |
It is important to note that the amount of RAM is retrieved by calling | |
the GlobalMemoryStatus() function, which reports a few hundred | |
kilobytes less than the amount of RAM physically installed. So, 128 MB | |
of RAM would typically be classified as "between 64 MB and 127 MB". | |
>>>> Real-world example | |
Let us have a look at a real-world example. On one of our test systems | |
the hardware information consists of the following eight bytes. | |
0xC5 0x95 0x12 0xAC 0x01 0x6E 0x2C 0x32 | |
Converting the bytes into H1 and H2, we obtain | |
H1 = 0xAC1295C5 and H2 = 0x322C6E01 | |
Splitting H1 and H2 yields the next table in which we give the value | |
of each of the bit-fields and the information from which each value is | |
derived. | |
dw & | | | |
offset | value | derived from | |
-------+-------+----------------------------------------------- | |
H1 0 | 0x1C5 | '1234-ABCD' | |
H1 10 | 0x0A5 | '00C0DF089E44' | |
H1 20 | 0x37 | 'SCSI\CDROMPLEXTOR_CD-ROM_PX-32TS__1.01' | |
H1 27 | 0x15 | 'PCI\VEN_102B&DEV_0519&SUBSYS_00000000&REV_01' | |
H2 0 | 0x1 | (unused, always 0x1) | |
H2 3 | 0x00 | (CPU serial number not present) | |
H2 9 | 0x37 | 'SCSI\DISKIBM_____DCAS-34330______S65A' | |
H2 16 | 0x0C | 'PCI\VEN_9004&DEV_7178&SUBSYS_00000000&REV_03' | |
H2 21 | 0x1 | 'PCI\VEN_8086&DEV_7111&SUBSYS_00000000&REV_01' | |
H2 25 | 0x1 | 'GenuineIntel Family 6 Model 3' | |
H2 28 | 0x3 | (system has 128 MB of RAM) | |
H2 31 | 0x0 | (system is not dockable) | |
>>> Using XPDec | |
XPDec is a utility to be run from the command prompt. It may be | |
invoked with one of four command line options to carry out one of four | |
tasks. | |
>>>> XPDec -i | |
This option enables you to access the information hidden in an | |
Installation ID. It decodes the Installation ID, decrypts it, and | |
displays the values of the hardware bit-fields as well as the Product | |
ID of your product. Keep in mind that the last three digits of the | |
Product ID contained in the Installation ID are randomly selected and | |
differ from the Product ID displayed by Internet Explorer. | |
The only argument needed for the '-i' option is the Installation ID, | |
as in | |
XPDec -i 002666-077894-484890-114573-XXXXXX-XXXXXX-XXXXXX-XXXXXX-XX | |
>>>> XPDec -p | |
To help you trace the origin of your Product ID, this option decodes a | |
Product Key and displays the Raw Product Key as it would be used in a | |
Product ID. | |
The only argument needed for the '-p' option is the Product Key, as in | |
XPDec -p FFFFF-GGGGG-HHHHH-JJJJJ-KKKKK | |
Note that this option does not verify the digital signature of the | |
Product Key. | |
>>>> XPDec -v | |
This option calculates the hash of a given volume serial number. It | |
was implemented to illustrate our description of string hashing. First | |
use '-i' to display the hardware bit-fields. Then use this option to | |
verify our claims concerning the volume serial number hash. | |
The only argument needed for the '-v' option is the volume serial | |
number of your system volume, as in | |
XPDec -v 1234-ABCD | |
(The volume serial number is part of the 'dir' command's output.) | |
>>>> XPDec -m | |
This option calculates the network adapter bit-field value | |
corresponding to the given MAC address. Similar to '-v' this option | |
was implemented as a proof of concept. | |
The only argument needed for the '-m' option is the MAC address of | |
your network adapter, as in | |
XPDec -m 00-C0-DF-08-9E-44 | |
(Use the 'route print' command to obtain the MAC address of your | |
network adapter.) | |
>> HARDWARE MODIFICATIONS | |
When looking at the effects of hardware modifications on an already | |
activated installation of Windows XP, the file 'wpa.dbl' in the | |
'system32' directory plays a central role. It is a simple | |
RC4-encrypted database that stores, among other things like expiration | |
information and the Confirmation ID of an activated installation, | |
a) the bit-field values representing the current hardware | |
configuration, | |
and | |
b) the bit-field values representing the hardware configuration | |
at the time of product activation. | |
While a) is automatically updated each time the hardware configuration | |
is modified in order to reflect the changes, b) remains fixed. Hence, | |
b) can be thought of as a snapshot of the hardware configuration at | |
the time of product activation. | |
This snapshot does not exist in the database before product activation | |
and if we compare the size of 'wpa.dbl' before and after activation, | |
we will notice an increased file size. This is because the snapshot is | |
added to the database. | |
When judging whether re-activation is necessary, the bit-field values | |
of a) are compared to the bit-field values of b), i.e. the current | |
hardware configuration is compared to the hardware configuration at | |
the time of activation. | |
>>> Non-dockable computer | |
Typically all bit-fields with the exception of the unused field and | |
the 'dockable' field are compared. If more than three of these ten | |
bit-fields have changed in a) since product activation, re-activation | |
is required. | |
This means, for example, that in our above real-world example, we | |
could replace the harddrive and the CD-ROM drive and substantially | |
upgrade our RAM without having to re-activate our Windows XP | |
installation. | |
However, if we completely re-installed Windows XP, the information in | |
b) would be lost and we would have to re-activate our installation, | |
even if we had not changed our hardware. | |
>>> Dockable computer | |
If bit 31 of H2 indicates that our computer supports a docking | |
station, however, only seven of the ten bit-fields mentioned above are | |
compared. The bit-fields corresponding to the SCSI host adapter, the | |
IDE controller, and the graphics board are omitted. But again, of | |
these remaining seven bit-fields, only up to three may change without | |
requiring re-activation. | |
>> CONCLUSIONS | |
In this paper we have given a technical overview of Windows Product | |
Activation as implemented in Windows XP. We have shown what | |
information the data transmitted during product activation is derived | |
from and how hardware upgrades affect an already activated | |
installation. | |
Looking at the technical details of WPA, we do not think that it is as | |
problematic as many people have expected. We think so, because WPA is | |
tolerant with respect to hardware modifications. In addition, it is | |
likely that more than one hardware component map to a certain value | |
for a given bit-field. From the above real-world example we know that | |
the PX-32TS maps to the value 0x37 = 55. But there are probably many | |
other CD-ROM drives that map to the same value. Hence, it is | |
impossible to tell from the bit-field value whether it is a PX-32TS | |
that we are using or one of the other drives that map to the same | |
value. | |
In contrast to many critics of Windows Product Activation, we think | |
that WPA does not prevent typical hardware modifications and, | |
moreover, respects the user's right to privacy. | |
>> ABOUT THE AUTHORS | |
Fully Licensed GmbH is a start-up company focusing on novel approaches | |
to online software licensing and distribution. Have a look at their | |
website at | |
http://www.licenturion.com | |
for more information. | |
Their research branch every now and then analyzes licensing solutions | |
implemented by other companies. | |
>> COPYRIGHT | |
Copyright (C) 2001 Fully Licensed GmbH (www.licenturion.com) | |
All rights reserved. | |
You are free to do whatever you want with this paper. However, you | |
have to supply the URL of its online version | |
http://www.licenturion.com/xp/ | |
with any work derived from this paper to give credit to its authors. |
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