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Grey Panther
Asked: 2009-12-26 09:02:50 +0800 CST

Are "unexportable" certificates a real security measure or just security theater?

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Recently I was working on recovering data from dead (bricked PSU) Windows XP machine, which included some client certificates installed into IE 6. I plugged in a temporary PSU and tried to export the certificate, only to be told that "these certificates are marked as non-exportable, and thus the private key can not be exported".

I've done some searching around the intertubes, however the only advices I could find were related to pre-install scenarios (ie. there is apparently an option which you can check during the installation to avoid this situation).

My questions would be:

  • Is this a real security measure? It seems to me that you can simply patch the verification logic in IE6 (or the CryptoAPI) and force the export of the certificate / private-key
  • Is there a ready-made tool to do this? (for backup purposes for example)
backup

3 Answers

  1. Best Answer

    Exporting private keys on certificates that have been marked non-exportable? Uh, how about a tool called Jailbreak...

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  2. "Unexportable" means the private key is inaccessible to CryptExportKey(). It might be possible to patch CryptoAPI in memory, but I haven't found any references to it.

    There also might be a way to load the registry "hive" in another system and either copy the certificates or edit the "unexportable" bit... but again, no such things on the googlenet.

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  3. Update:

    There is a new version of mimikatz that also supports CNG Export (Windows Vista / 7 / 2008 ...)

    1. download (and launch with administrative privileges; trunk version for last version)
    2. privilege::debug (or not if you're already system or target only CryptoApi)
    3. crypto::patchcng (nt 6) and/or crypto::patchcapi (nt 5 & 6)
    4. crypto::exportCertificates and/or crypto::exportCertificates CERT_SYSTEM_STORE_LOCAL_MACHINE

    pfx files are passwords protected "mimikatz"

    Old post:

    Maybe can you try another tool with other private keys functions : "mimikatz", it export other keys that other cannot export (non exportable, medium protected, orphan, etc..) The "bit" is not altered on system file, only the program context is altered :) For example, an user (not administrator) can export his own protected / non exportable keys without particulars rights.

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