[Full-Disclosure] Vulnerability: protected Adobe eBooks can be copied between computers
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From: email@example.com (firstname.lastname@example.org) Date: Tue, 30 Jul 2002 18:37:48 +0400
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Product Vulnerability Reporting Form
Adobe Content Server (now in use by more than 300 online retail sites) enables
the distribution of eBooks and electronic documents from any Web site as PDF
files with complete Digital Rights Management (DRM). To prevent unauthorized
reading or copying of eBooks, the Acrobat eBook Reader (client software for
reading eBooks) does not allow to read the same eBooks from more than one
computer or to copy eBook and data files from one computer to another. However,
there are a few defects in the implementation of this protection in Acrobat
eBook Reader, so eBooks can be still copied across different computers.
Name : ElcomSoft Co.Ltd.
E-mail : email@example.com
Phone / fax : +7 095 216-7937
+1 866 448-2703 (fax; US, toll-free)
Affiliation and address: 2-171 generala Antonova st.
Vendor (Adobe has been notifed about this vulnerability at July 23,
2002, but have hot replied.
Description of the vulnerability.
Adobe Content Server (http://www.adobe.com/products/contentserver/) makes it
easy for you to sell electronic books (eBooks) securely online. Adobe Content
Server packages and protects eBooks and distributes them in PDF format
directly from any Web site. Anyone with the free Adobe Acrobat eBook Reader
(http://www.adobe.com/products/ebookreader/) can purchase your content with
ease. When the file is encrypted, special master voucher for its distribution
is being created. The master voucher is a separate, XML-based file that
contains an encrypted key to the eBook and the set of privileges that
accompany it. When a customer purchases an Adobe PDF eBook directly from an
e-commerce site, it's automatically downloaded into the customer's personal
Acrobat eBook Reader library for immediate viewing. Acrobat eBook Reader
unlocks the encrypted key that came with the eBook and its master voucher.
Now the eBook is tied to the customer's Acrobat eBook Reader and can't be
transmitted elsewhere (by design) -- every other copy of the Reader uses
another (unique) encryption keys, so eBook purchased from one computer
cannot be open on other computers.
On January 29, Adobe representative (Mr. Thomas R. Dıaz, the Senior
Engineering Manager for eBook Development Group at Adobe Systems Incorporated),
advised that it is possible to back up collection of eBooks from one computer
and restore them to a different machine by making use of a back up feature
built into the Adobe eBook Reader (note: this process operates successfully on
your entire library of Adobe eBook Reader files regardless of where you
obtained them from and does not require you to consult with the ebookstore
that you purchased from):
Backing Up Adobe Acrobat eBook Reader eBooks
1. Make a copy of the 'Data' folder (including 'Vouchers' subfolder)
2. Install Adobe eBook Reader on another machine
3. Restore the 'Data' folder over the corresponding 'Data' folder in your
freshly installed Adobe Acrobat eBook Reader
4. Open Adobe Acrobat eBook Reader and attempt to open one of the eBooks.
You will receive the following message:
Voucher Update Required (Version 2.2 Build 203)
You will not be able to read your eBooks until you update you
installation of Acrobat eBook Reader. Please contact Adobe Systems
Customer Support at http://www.adobe.com/suport/[...] for assistance
in completing this update.
Challenge: E7P6 4K2D 7MU3 VUDT
5. Ring Adobe, quoting the Challenge code, then receive an Activation code.
6. eBooks can now be reopened.
However, activation code can be easily obtained for any given Challenge
without calling Adobe. Here is how Adobe Acrobat eBook Reader verifies the
1. The 'Challenge' is being encrypted using popular symmetric block cipher;
the encryption key (actually, there are two keys: one in Reader 2.1 and
older, and another in Reader 2.2) is constant and stored inside the
Adobe eBook Reader executable.
2. Encrypted 'Challenge' is being hashed using another popular algorithm.
3. First 10 bytes of the hash value (converted from binary to text using
MIME-like encoding) is the proper Activation code -- the Reader just
compares it with the one entered to the Reader.
The details (the names of the ciphers, and the encryption keys) are not
provided here for security reasons.
The impact of this vulnerability.
Even using standard method (by calling Adobe to receive proper Activation
code), anybody can create illegal copies of "protected" Adobe eBooks. But
even worse, any person with a basic knowledge of crypto algorithms can
write a program to generate an Acivation code from the Challenge, so
eliminating 'calling Adobe' step completely.
Workarounds and/or fixes.
No ones available at the moment. But to implement reliable and
secure challenge-response scheme, it is not enough just to "use
sophisticated, industry-standard levels of software encryption" - it
is necessary to use them *properly*.
The Activation code should be calculated at Adobe using asymmetric
algorithm like RSA (with a private key, known only to Adobe), while
the Reader should decrypt it using public key, and compare the
result with the Challenge. So the Reader itself will not contain
enough information needed to make proper Activation code from the
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