RSA keys under 1024 bits are blocked
Public key based cryptographic algorithms strength is determined based on the time taken to derive the private key using brute force methods. The algorithm is deemed to be strong enough when the time required to derive private key is prohibitive enough using the computing power at disposal. The threat landscape continues to evolve. As such, we are further hardening our criteria for the RSA algorithm with key length less than 1024 bits.
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.
Some issues that you may encounter after applying this update may include:
- Error messages when browsing to web sites that have SSL certificates with keys that are less than 1024 bits
- Problems enrolling for certificates when a certificate request attempts to utilize a key that is less than 1024 bits
- Creating or consuming email (S/MIME) messages that utilize less than 1024 bit keys for signatures or encryption
- Installing Active X controls that were signed with less than 1024 bit signatures
- Installing applications that were signed with less than 1024 bit signatures (unless they were signed prior to January 1, 2010, which will not be blocked by default)
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 security advisory is located at http://technet.microsoft.com/security/advisory/2661254.
- The KB article is available at http://support.microsoft.com/kb/2661254.