Microsoft, the NSA, and You

Here is the press release; for the full details, look here.

A sample program which replaces the NSA's key is here.

FOR IMMEDIATE RELEASE 

Microsoft Installs US Spy Agency with Windows 

Research Triangle Park, NC - 31 August 1999 - Between Hotmail hacks and
browser bugs, Microsoft has a dismal track record in computer security. Most
of us accept these minor security flaws and go on with life. But how is an IT
manager to feel when they learn that in every copy of Windows sold, Microsoft
has installed a 'back door' for the National Security Agency (NSA - the USA's
spy agency) making it orders of magnitude easier for the US government to
access their computers? 

While investigating the security subsystems of WindowsNT4, Cryptonym's
Chief Scientist Andrew Fernandes discovered exactly that - a back door
for the NSA in every copy of Win95/98/NT4 and Windows2000. Building on
the work of Nicko van Someren (NCipher), and Adi Shamir (the 'S' in
'RSA'), Andrew was investigating Microsoft's "CryptoAPI" architecture
for security flaws. Since the CryptoAPI is the fundamental building
block of cryptographic security in Windows, any flaw in it would open
Windows to electronic attack.

Normally, Windows components are stripped of identifying information. If the
computer is calculating "number_of_hours = 24 * number_of_days", the only
thing a human can understand is that the computer is multiplying "a = 24 * b".
Without the symbols "number_of_hours" and "number_of_days", we may have no
idea what 'a' and 'b' stand for, or even that they calculate units of time. 

In the CryptoAPI system, it was well known that Windows used special numbers
called "cryptographic public keys" to verify the integrity of a CryptoAPI
components before using that component's services. In other words, programmers
already knew that windows performed the calculation "component_validity =
crypto_verify(23479237498234...,crypto_component)", but no-one knew exactly
what the cryptographic key "23479237498234..." meant semantically. 

Then came WindowsNT4's Service Pack 5. In this service release of software
from Microsoft, the company crucially forgot to remove the symbolic
information identifying the security components. It turns out that there are
really two keys used by Windows; the first belongs to Microsoft, and it allows
them to securely load CryptoAPI services; the second belongs to the NSA. That
means that the NSA can also securely load CryptoAPI services... on your
machine, and without your authorization. 

The result is that it is tremendously easier for the NSA to load unauthorized
security services on all copies of Microsoft Windows, and once these security
services are loaded, they can effectively compromise your entire operating
system. For non-American IT managers relying on WinNT to operate highly secure
data centers, this find is worrying. The US government is currently making it
as difficult as possible for "strong" crypto to be used outside of the US;
that they have also installed a cryptographic back-door in the world's most
abundant operating system should send a strong message to foreign IT managers.

There is good news among the bad, however. It turns out that there is a flaw
in the way the "crypto_verify" function is implemented. Because of the way the
crypto verification occurs, users can easily eliminate or replace the NSA key
from the operating system without modifying any of Microsoft's original
components. Since the NSA key is easily replaced, it means that non-US
companies are free to install "strong" crypto services into Windows, without
Microsoft's or the NSA's approval. Thus the NSA has effectively removed export
control of "strong" crypto from Windows. A demonstration program that replaces
the NSA key can be found on Cryptonym's website. 

Cryptonym: Bringing you the Next Generation of Internet Security,
using cryptography, risk management, and public key infrastructure. 

Interview Contact:
   Andrew Fernandes
   Telephone: +1 919 469 4714
   email: andrew@cryptonym.com
   Fax: +1 919 469 8708 

Cryptonym Corporation
1695 Lincolnshire Boulevard
Mississauga, Ontario
Canada  L5E 2T2 

http://www.cryptonym.com 

# # #

The Full Details

These details are essentially the contents of the "Rump Session" talk that Andrew Fernandes gave at the Crypto'99 Conference, on 15 August 1999, in Santa Barbara, California.

An Overview of the Microsoft's CryptoAPI

Microsoft's CryptoAPI allows independent software vendors (ISVs) to dynamically load Cryptographic Serivce Providers (CSPs) as in the following diagram:

This arrangement of having Windows verify the CSP signature is what allows Microsoft to add cryptographic functionality to Windows. They will not digitally sign a CSP unless you first agree to abide by US export rules. Translation: Microsoft will not allow non-US companies to add strong crypto functions to Windows.

Fortunately, the verification of the CSP's digital signature opens up a security flaw in this picture.

Observations

Using NT4 Server, SP5 (domestic, 128-bit encryption version), and Visual C++ 6, SP3. These same results have been found in Win95osr2, Win98, Win98gold, WinNT4 (all versions), and Win2000 (up to and including build 2072, RC1).

Before CSP loading		in ADVAPI32.DLL
Address 0x77DF5530	->	A9 F1 CB 3F DB 97 F5 ... ... ...
Address 0x77DF55D0	->	90 C6 5F 68 6B 9B D4 ... ... ...
After RC4 encryption using		we see
A2 17 9C 98 CA	=>	R S A 1 ... 00 01 00 01 ... (looks like an RSA public key)
A0 15 9E 9A CB	=>	R S A 1 ... 00 01 00 01 ... (looks like an RSA public key)
Looking at SP5 debugging symbols		in "_CProvVerifyImage@8"
Address 0x77DF5530	<-	has data tag "_KEY"
Address 0x77DF55D0	<-	has data tag "_NSAKEY"

Screenshots One, Two, Three, Four, and Five showing the actual debugging information.

The Flaw

An attack:

• Replace "_KEY" with your own key...
• ...but Windows will stop working since it cannot verify it's own security subsystem!

An better attack:

• Replace "_NSAKEY" with your own key...
• ... Windows keeps working, since Microsoft's key is still there
• stops the NSA
• works becaus Windows tries to verify the CSP first using "_KEY", and then silently fails over to "_NSAKEY"

The Result:

• Windows CryptoAPI system still functional
• the NSA is kicked out
• the user can load an arbitrary CSP, not just one that Microsoft or the NSA signed!

Implications

1. What is the purpose of "_NSAKEY"? Espionage? Or do they simply not want to rely on Microsoft when installing their own CSPs?
2. Using RSA's Data Security's (now Security Dynamics) "BSafe" toolkit actually makes analysis of a program easier.
3. We do not need to modify the "advapi32.dll" file in order to remove the NSA key, nor do we need special privilleges on the machine.
   1. use self-modifying code
   2. needs undocumented vxd calls under Win95 and Win98
   3. needs special memory features under WinNT and Win2k
4. It is easy for any process to bypass any CSP and substitute its own.
5. Export controll is effectively dead for Windows.
6. Note for Win2k - there appear to be three keys in Win2k; Microsoft's, the NSA's, and an unknown third party's. Thanks to Nicko van Someren for bringing this to our attention.

Removing the NSA

A sample program which replaces the NSA key with a test key, and leaves the rest of the CryptoAPI system intact, can be downloaded here (currently only for WinNT and Win2k). These files are provided for demonstration purposes only, and may not be redistributed or used for any purpose other than demonstration without the written authorization and license of Cryptonym Corporation. For more information, please contact:

Andrew Fernandes 
email: andrew@cryptonym.com
Phone +1 919 469 4714
Fax   +1 919 469 8708