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TUCoPS :: Windows :: xpact.txt

Inside Windows XP Product Activation

Inside Windows XP Product Activation

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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

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
It implements the algorithms presented in this paper. Reading its
source code, which is available from the same location, is highly

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.


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


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

>>> 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

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

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

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


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

>>>> 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


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


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


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

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

>>>> 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


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.)


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

a) the bit-field values representing the current hardware


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

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.


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

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.


Fully Licensed GmbH is a start-up company focusing on novel
approaches to online software licensing and distribution.

Related Hyperlinks

WinXP product activation cracked

Windows Product Activation compromised

German press release (ASCII, 4.4 kb)
XPDec executable (zipped, 25.2 kb)
XPDec executable (self-extracting, 48.7 kb)
XPDec source code (zipped VC project, 49.4 kb)  (Only the
executables contain the cryptographic key.)

Credits and Copyrights

Fully Licensed GmbH, Rudower Chaussee 29, 12489 Berlin, Germany

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