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Security, Technology

Need help: Removing old certificate revocation lists in Windows

July 9th, 2009 by Jeff | Dump Core

I have a bit of a quandary that’s got me effectively stuck on a task at my day job. Thus far, Google and every other resource I’ve searched have been little help. In the unlikely event somebody out there that reads this blog (or at least gets the update notices via RSS, Twitter, or the other various feeds) can help me, I’m going throw this out and hope it garners some feedback.

I’ll try to keep this as short as possible. Our production Web site, built in ASP.NET and C# and running in IIS on Windows Server 2003, recently added authentication via client certificates stored on users’ smart cards. We allow users to attach their smart card certificates to their existing account, then authenticate them by verifying their certificate, looking up the user account by that certificate’s fingerprint, and loading their profile. These certificates are signed by a trusted third-party certificate authority (CA) owned by the client and every morning we download the latest certificate revocation lists (CRLs) so we can reject certificates as they are revoked by the CA. My download process is working fine and dandy, so that’s not the problem; neither is the actual import process, as I know the command line options for Microsoft’s certutil command that will import the CRLs.

My problem stems from removing the old CRLs, which so far I haven’t been able to accomplish without going into the Microsoft Management Console and clicking through the GUI. We’ve had problems with the size of the certificate store, as the CRLs tend to be very large and we have to remove the old ones before the new ones can be imported. I’ve tried the few suggestions I’ve found online that haven’t seemed to work, such as a command-line switch for certutil that’s supposed to overwrite the old CRL with the new one (it just imports the new one and leaves the old one in place). We want to automate this process into a scheduled task, so it can run early in the morning when our users aren’t on the system and without human intervention.

Here are the tools available to me:

  • As previously stated, certutil (part of Microsoft’s Certificate Services package);
  • Windows PowerShell;
  • Anything I can throw into a .NET assembly and build an executable out of (preferably C# code);
  • Good old fashioned batch files.

I’ll tell you, I’m pretty frustrated and exhausted by this task. It’s not that I can’t do the research and figure it out for myself; I have done the research, and everything I’ve read applies to certificates and not CRLs, and they’re not exactly a direct swap in usage. I’d prefer not to provide much more detail than this for security reasons.

For the time being, I’ve been manually removing the old CRLs through MMC and then running a batch script to do the import every morning as my first task. That’s working fine for now, when I’m in the office every morning, but I’ll be taking some vacation time soon that will start to cause problems. I swear, if this was OpenSSL and Apache on Linux, I’d have this solved in a heartbeat (or at least an afternoon). If you have any suggestions, please feel to post a comment or shoot me a direct e-mail at the usual address.

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