Microsoft roots out obsolete MD5 certificates, disallows RSA keys shorter than 1024 bits

In August, Windows computers will receive a critical update via Windows Update.  The patch is designed to close a security loophole in Windows' encryption that is being actively exploited by malware authored by the U.S. government and Israel.

I. Exploiting Trust in Microsoft

Currently, Windows allows 256-, 384-, and 512-bit keys.  Some Microsoft Corp. (MSFT) Terminal Server Licensing (MSTL) certificates until recently also used the weak MD5 hashing algorithm, despite the algorithm being officially discontinued in 2009.

The weaknesses, both on the hashing and the key-length front, allowed "world-class" malware authors -- believed to be in the employ of the U.S. government and Israel -- to write a piece of malware called Flame, which uses a MTSL certificate cracked by a hitherto unknown attack called MD5 chosen prefix collision.

Certificate in hand, Flame was able to masquerade as a Windows Update from the ultimate trusted source in the Windows world -- Microsoft.  Thus the malware quickly proliferated in its intended target location -- Iran and the Middle East.

Flame infographic
Flame has narrowly targeted the Middle East, particularly Iran. [Image Source: Kapersky Labs]

II. Microsoft Fights Back With Patch

Kurt L. Hudson, a senior technical writer at Microsoft, has posted a Windows PKI blog regarding next month's Windows Update, which is expected to tighten key restrictions to prevent further abuse.

He writes:

To further reduce the risk of unauthorized exposure of sensitive information, Microsoft has created a software update that will be released in August 2012 for the following operating systems: Windows XP, Windows Server 2003, Windows Server 2003 R2, Windows Vista, Windows Server 2008, Windows 7, and Windows Server 2008 R2. This update will block the use of cryptographic keys that are less than 1024 bits.
To prepare for this update, you should determine whether your organization is currently using keys less than 1024 bits. If it is, then you should take steps to update your cryptographic settings such that keys under 1024 bits are not in use.

The update could render applications with signatures shorter than 1024-bits unable to install.  It may also create difficulties with certain websites, SSL certificates, and Active X controls.  

Windows key chain error
Shorter keys will no longer be considered valid in Windows. [Image Source: Microsoft]

Corporate users are given a series of suggestions to prepare the signature length bump.  It remains to be seen exactly how difficult the transition will be for everyday consumers.

1024-bit signatures will be short-lived, as well.  The National Institute of Science and Technology in 2011 designated [PDF] Dec. 31, 2013 as the official target date to black out 1024-bit key encryption using the RSA and DSA algorithms.

key in door
Key-based encryption algorithms are only as secure as the enemy is weak hardware- and algorithm-wise. [Image Source: Margie Stibora]

The security community must constantly bump encryption algorithm strength and length in the face of ever increasing computing power and clever new attacks.  No encryption standard is safe from individuals with sufficient computing power and savvy in the long run -- even quantum encryption has proved susceptible to attacks on the hardware used to encrypt the quantum bits (qBits).  Thus security is measured in fleeting moments of safety, using technology that in years will be rendered useless.

III. Did the U.S. go to War With Iran?

Since Flame was discovered, Microsoft has also conducted a vigorous screen of its licensing certificates and discovered 28 other certificates that did not live up to its current standards, but had escaped correction in past cleanups.

Flame remains a hot topic, as both it and Stuxnet are the subject of lively debate over whether the U.S. "declared war" on Iran by unleashing the malware on it.   

Flame worm
Rooting out the Flame worm is a top priority for Microsoft. [Image Source: Krishnan Vasuvedan]

Presidents George W. Bush Jr. and Barack H. Obama both allegedly authorized the use of the malware against the Asian nation.  Stuxnet primarily targeted Iran's nuclear weapons refining facilities, while Flame offered a general attack on Iran's oil industry -- one of the key sources of GDP for the nation.

Source: Microsoft

"We don't know how to make a $500 computer that's not a piece of junk." -- Apple CEO Steve Jobs

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