Recently
I was asked an advice about Lok-it encrypted USB keys which presented
4 interesting points :
-
hardware AES256-CBC encryption
-
FIPS 140-2 level 3 certification
-
trusted path for pin entry (physical pin pad)
-
fully hardware system, no need to execute untrusted code or require
admin privileges
The
two questions were : is it a secure product ? and Is it backdoored ?
Before
focusing on this particular product, let's have a look on security
issues related to encrypted USB sticks.
Secure
Sticks
Numerous
USB encrypted devices had some security issues (yes, even with 256 bit AES
encryption and FIPS 140-2-L2 certification), and as a blackbox system
it is difficult to assess the quality of the implementation.
It
is very important to remember that the quality of the implementation
and the operational conditions of use are as important as the quality
of the algorithm of the key length ; and that a FIPS certification
does not make a product secure.
But
unfortunately marketing always focuses on algorithm, length and
certification.
Example
of broken secure Sticks
Some
excellent analysis of encrypted devices can be found on SpritesMods
site.
SySS
made also a very good analysis of different products.
A
very good example is the QNAP crypto backdoor (based on LUKS, when
the users creates a key, a second one is automatically generated and
hidden in the flash memory ; but easily retrievable)
Crypto-backdoors
The
previous examples were “implementation errors” or “basic”
crypto backdoors, but much more subtle ones can be
designed, see :
Chapter
10: An Elliptic Curve Asymmetric Backdoor in OpenSSL RSA Key
Generation
BuildingRobust Backdoors in Secret Symmetric Ciphers
, Adam L. Young MITRE
Corporation
joint work with Moti Yung Columbia Univ./RSA Labs
BlackHat 2005
Back
to Lock-it
I
did not make a security evaluation of this product, but as it is
derived from a ClevX technology, which is FIPS certified, we can have a look at the
FIPS security policy. Some parts seems interesting :
“LOK-IT®
is pre-programmed with a unique set of encryption keys created during
the manufacturing process. A list of 6 AES keys is supplied by a
random number generator
(RNG) executing on the manufacturer's
computer. The RNG complies with ANSI X9.31
Appendix 2.4
specification for the generation of random numbers.” (p7)
If
you were wondering were a potential crypto backdoor could be
placed
... I'm not actually saying that the product is backdoored or
not, but that if I had to backdoor the product, this would be a nice
place among others.
Especially if the manufacturer uses a good RNG and keeps a copy of the keys : he can access the data but he is the only one (we do not consider here other persons who may access the key escrow system ; or legal compelling), and the device is secure for your own use.
Especially if the manufacturer uses a good RNG and keeps a copy of the keys : he can access the data but he is the only one (we do not consider here other persons who may access the key escrow system ; or legal compelling), and the device is secure for your own use.
Note
: having keys which do not only depend on the PIN code is a good
thing as the entropy of a 7 number PIN code is terribly low)
“Each
LOK-IT® module is manufactured with 6 AES encryption keys. Only 1 of
these keys is
used to encrypt / decrypt data. The remaining 5 keys
have no relationship to stored data.
When zeroization occurs, the
AES encryption key at the top of the list is erased; the next
key
becomes the key used to encrypt the private partition. Given enough
zeroizations, all
keys will be consumed and the drive becomes
inoperable.
”
This
is rather a good thing (not as good as an embedded smart card, but
for the price it is a good deal), as keying material is zeroized
after a set of wrong attempts, rather than a simple time delay.
The
trusted path is also a very good thing, avoiding keyloggers related
issues (both OS and hardware).
Some
other information from the sec pol :
Physical
security
“•
Production grade
components
•
Hard, opaque epoxy
covering the cryptographic boundary
•
EEPROM memory protect
fuse is set in the security controller
”
“The
module is a multi-chip standalone cryptographic module, as defined by
FIPS 140-2 and
consists of an Initio 1861 USB controller, NAND Flash
memory and a Microchip PIC16F688
security controller. All components
are encased in hard, opaque, production grade
integrated circuit
packaging. The cryptographic boundary is defined as the boundary of
the
module's PCB and hard epoxy coating.
”
By
the way ClevX pro technology is used in Corsair Padlock 2 (same as the
non FIPS Lok-it) and
the Datalock Personal is used in SDG Secret Diary
Conclusion
Is
it backdoored ?
Without
a proper security analysis we can not say if there is or not a
backdoor, but as the crypto system is hardware implemented and as we
don't have the hand on the key generation process we can not assume
that the device implementation is secure.
Also
I don't like the idea on relying on manufacturer generated keys (I do
not only wonder about the quality of the (P)RNG, but also about the
risk of a keys copy being kept).
Even
if we could load our own keys, a backdoor can still allow an attacker
to retrieve the key : for example by sending specific commands to the
microchip which will directly surrender the key, or specific commands which will just bypass the PIN verification process, etc.
In
a few words : or you can trust the system, by having access to the
full implementation (software and hardware) and checking it or
have it validated by a trusted organization which will perform a full
analysis (FIPS, EAL, etc is not sufficient by itself).
Remember
also that numerous manufacturers tend to add backdoors, for
“recovery” purposes or at law enforcement agencies request.
I'm not saying that Lok-it or ClevX backdoored the product. I am only saying just that this kind of “enhancement” is a tradition in the crypto industry (see Général Jean-Louis Desvignes lesson at INSA Lyon, in French).
I'm not saying that Lok-it or ClevX backdoored the product. I am only saying just that this kind of “enhancement” is a tradition in the crypto industry (see Général Jean-Louis Desvignes lesson at INSA Lyon, in French).
So
is it a good product ?
Well
as always, it depends on the use and the security target.
High
security use
Especially
if you need assurance of the correct implementation of the crypto
system (in France we are a bit “sensitive” on crypto sovereignty,
especially when we have to rely on US/UK blackbox crypto systems –
even when US products are often much better and/or cheaper than their French equivalents),
I would advice to stick to open source, evaluated and well
engineered software such as truecrypt, LUKS or GPG but you have
to keep in mind all the issues linked to software encryption ; and if
possible use it with a smartcard.
Of
course, if you are working for a company which is allowed to buy
government accredited encryption products, there is no such
question.
Other
cases
When
the information is sensitive but not confidential, Lok-it FIPS seems
to be a very good product : very competitive price, trusted path for
PIN entry, intuitive use, OS independent and FIPS 140-2 L3 (which is not a full guarantee of security, but at least validates some points, especially as cryptographic operations and PIN entry only take place on the key)
In
a lot of cases it is preferable to have an untrusted encryption system
always used rather than a high level encryption system scarcely used
because it is too complicated to use in operational conditions.
We
often encounter this issue during audits, when we have to retrieve
data from a server where we are not allowed to install a software, or
if we have to share the data with non IT persons which may have some
difficulties to use crypto software.
At
least with this kind of USB key, it is impossible not to encrypt the
data, and the PIN is not entered on and untrusted system ; even if
the user is not security aware, very tired or under heavy stress.
The
OS independence is also very interesting when you have to deal with
different populations (ex : design team using MAC, sysadmins using Un*x).
So
I would recommend to use by default hardware encrypted USB keys, and
for sensitive information use a truecrypt/dmcrypt-LUKS partition on
top of it.
But
always consider the device as “password protected” rather than
“securely encrypted” ; and of course to securely backup the data.
Note
: A nice combination would be to install a bootable linux on the
stick : this will make it much more difficult for an attacker to
tamper the kernel (I would still recommend to encrypt the root with
dmcrypt-LUKS)
Note 2 : the GPF Crypto Stick v2 seems very promising (encypted storage + a GPG card)
Note 2 : the GPF Crypto Stick v2 seems very promising (encypted storage + a GPG card)
===============
Case
examples :
SanDisk
Cruzer Enterprise - FIPS Edition
http://www.syss.de/fileadmin/ressources/040_veroeffentlichungen/dokumente/SySS_Cracks_SanDisk_USB_Flash_Drive.pdf
(the paper also refers to flawed MXI Security FIPS 140-2-L2 keys).
Here
are the main parts :
“• FIPS
140-2 level 2 certified
• Hardware
based 256-bit AES encryption
• Mandatory
access control for all files (100% private partition)
• Strong
password enforcement
• “Lockdown”
mode when a set number of incorrect password attempts is made
”
“The
reason for this is the way how user-supplied passwords are verified.
The first security
problem here is that the actual password
verification is not done in hardware – i.e. on
the USB mass
storage device itself – but in software on the PC of the user. This
fact
makes it possible to analyze the password-based authentication
process in detail with
the help of a software debugger like OllyDbg2
, for instance. The second and bigger
problem is, however, that
secure cryptographic algorithms, like AES in this case, are
used in
an insecure way.
”
“The
research of the SySS GmbH showed that the password verification works
in the
following way:
1.
The user-supplied password is converted from ASCII to WideChar
2.
A MD5 hash of the WideChar password is calculated
3.
A ASCII-HEX representation of the MD5 hash is generated and also
converted to
WideChar;
the first half of the result serves as key in the next step
4.
With the generated key, 32 bytes of data, which have been read from
the USB flash
drive
before, are decrypted via AES-256-ECB
5.
If the result of the decryption corresponds with a specific value,
the password is
correct and the protected data storage of the USB
flash drive can be accessed
In
the course of the security analysis it was found out that the result
of the decryption
in step 5 was always the same when supplying the
correct password. This did not
even change when a new password was
set or when the USB flash drive was formatted.
The
reason for this is that when setting a new password, always the same
32 bytes
are encrypted via AES-256-ECB and therefore must
consequently be the result of the
decryption during the password
verification process.
”
“In
order to gain access to the protected mass storage of the USB flash
drive, one just
has to make sure that the password verification
always results in these 32 bytes. In the
further login process those
32 bytes are used for unlocking the protected partition of the
USB
flash drive.” and “makes it possible to gain access to all stored
data by just a few mouse clicks fairly easily
”
ThumbDrive
CRYPTO
This
one also is very interesting :
“ThumbDrive
R CRYPTO ensures that 100% of the storage area is encrypted.
With
this 256-bit hardware AES engine, the ThumbDrive R CRYPTO offers
one
of the most advanced security solutions available today
”
Here
are the main parts :
“A
further analysis showed that the device configuration including the
administrative
password is stored in a special memory of the USB
flash drive. When the program
SecureLogin.exe is started, the device
configuration is read from this memory using a
controller-specific
command. In each reading operation one 8K data block (8192 bytes)
is
copied from the USB flash drive to the host PC.
”
“The
administrative password is stored in an encrypted manner (marked red)
along with
the
used encryption key (marked green). To be precise, only the first
eight characters
of
the password are encrypted (byte sequence 7FAB977474776DA6), the
remaining six
characters
are stored in plaintext (byte sequence 627230783432, which is the
ASCII
string
“br0x42”).
As
figure 4 illustrates, the used encryption algorithm is very simple
and completely
reversible
in contrast to cryptographically secure one-way hash algorithms. The
first 8
characters
are encrypted by adding the value of the one byte long encryption key
(26h)
followed
by a bitwise not-operation.
”
“In
the course of the security analysis, the SySS GmbH developed a
proof-of-concept
software tool for demonstration purposes. This
software tool named ThumbDrive
CRYPTO Unlocker extracts the correct
administrative password and automatically
unlocks the protected mass
storage device of a TREK ThumbDrive CRYPTO USB
flash drive with a
single mouse click. Figure 10 shows this proof-of-concept software
tool
in action.”
QNAP
crypto Backdoor
Even
when products rely on well engineered software like LUKS, it can be
poorly implemented or intentionally backdoored. For instance in this
case, when the user creates a new key, a second one is generated,
obfuscated and then stored in the flash memory. Accessing the data
can be easily done by reading the “backup” key, and
de-obfuscating it (and everything is documented here
http://www.baseline-security.de/downloads/BSC-Qnap_Crypto_Backdoor-CVE-2009-3200.txt).
“When
a user selects in the web GUI to encrypt a hard drive, he has to
supply a passphrase of 8-16 length. The Qnap solution is to use the
underlying Linux standard mechanisms of LUKS to create the encrypted
partition. The user supplied passphrase is crypt(3)'ed with the MD5
salt of $1$YCCaQNAP$ and used as the initial key to access the LUKS
master key for the drive.
Additionally,
the system creates a second key, which is 32 characters long and
contains all low case characters and the numbers 0-9, and adds it to
the LUKS keyring: /sbin/cryptsetup luksAddKey /dev/md0
/tmp/temp.wLbZNp --key-file=/tmp/temp.rUBxFo”
Source
: http://www.securityfocus.com/archive/1/506607
(2010)
Source: http://www.zdnet.co.uk/news/security-threats/2010/01/04/kingston-flash-drives-suffer-password-flaw-39963327/
(2010)
"Kingston Technology has asked customers to return certain models of its DataTraveler secure flash drives for an update, following the discovery of a flaw in the memory sticks.
The affected models include the DataTraveler BlackBox; DataTraveler Secure — Privacy Edition; and DataTraveler Elite — Privacy Edition."
Source: http://www.zdnet.co.uk/news/security-threats/2010/01/04/kingston-flash-drives-suffer-password-flaw-39963327/
