Microsoft Warns Of Looming Digital Certificate Deadline

To improve Windows security, a Microsoft security update soon will block access to RSA digital certificates that have a key length of less than 1,024 bits.



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Memo from Microsoft to Windows administrators: Make sure all of your digital certificates have at least 1,024 bits.

That warning comes as Microsoft prepares to release an automatic security update for Windows on Oct. 9, 2012, that will make longer key lengths mandatory for all digital certificates that touch Windows systems.

Notably, Internet Explorer won't be able to access any website secured using an RSA digital certificate with a key length of less than 1,024 bits. Likewise, without a strong enough certificate, certificate authority service in Windows won't be able to start, ActiveX controls might be blocked, users might not be able to install applications, and Outlook 2010 won't be able to encrypt or digitally sign emails, or communicate with an Exchange server for SSL/TLS communications. In addition, Microsoft warned that after its security update, Operations Manager will be unable to monitor--or discover new instances of--any HP-UX PA-RISC computers that don't have an RSA digital certificate of least 1,024 bits.

Microsoft's move reflects the relative ease with which digital certificates of less than 1,024 bits can now be cracked--or derived--via brute-force attacks. "The private keys used in these certificates can be derived and could allow an attacker to duplicate the certificates and use them fraudulently to spoof content, perform phishing attacks, or perform man-in-the-middle attacks," according to Microsoft.

[ Read Cryptographers Discover Public Key Infrastructure Flaw. ]

The "fix" for keeping up with Microsoft's mandatory security improvement is simple. "For those who find they are using certificates with RSA key lengths of less than 1,024 bits, those certificates will be required to be reissued with at least a 1,024-bit key length," according to a Microsoft Security Resource Center blog post. It also noted that "1,024 should, by the way, be considered a minimum length; the most up-to-date security practices recommend 2048 bits or even better."

Microsoft's security update is available now for download. The company recommends that IT administrators gain familiarity with it, and test any existing processes that might break, before it releases the update via Microsoft Update in October. To help, a Microsoft knowledgebase article, Microsoft Security Advisory: Update for minimum certificate key length details tips and techniques for discovering any digital certificates in use that have a key length of less than 1,024, as well as recommendations for updating them.

The timing of Microsoft's digital certificate spring cleaning has no doubt been driven by the Flame malware, discovered in May, and inside which security experts found built a "collision attack" against the Microsoft Terminal Services encryption algorithm, which allowed the malware to successfully spoof that Windows service and automatically install itself on targeted PCs.

In the eyes of Marc Stevens, a crypto-analyst at the Centrum Wiskunde and Informatica (CWI) in Amsterdam who studied Flame, whoever created that collision attack was practicing "world-class cryptanalysis." But when it comes to malware attacks, what's leading edge quickly becomes commonplace, as known attack techniques get emulated by other attackers, and included as automated options in crimeware toolkits and the open source Metasploit penetration testing toolkit.

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