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As part of my forensics, I want to determine if a given certificate has any indicator of which PKI software was used to create it.

So far, I see differences in the following properties for a Certificate Authority:

  • Serial Number (format, length, is ( not) random)
  • Issuer value (may align with internal AD forest name in MSFT)
  • Presence of "Certificate Template Information" (MSFT)
  • CRL Distribution Point contains a server name
  • Subject contains "DC = " (MSFT) versus other properties such as O, C present in Google.com

I'm sure there are comparable differences in end entity certificates, and CRL/CRL Dif certificates.

Question

  • Is there any resource that investigates the differences between the certificate output from various CA's (or makecert.exe for that matter)?

  • Is there any byte level fingerprinting within a certificate? (or is everything exposed via a certificate export?

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Not a direct answer, but maybe hints in the right direction

Cert linters

These might be interesting to spot anomalies: There is Peter Bowen's certlint (written in Ruby) and Kurt Roeckx's x509lint. Both of these are integrated into crt.sh. Here are some examples with interesting anomalies: cert for *.gmaptiles.co.kr and example.com

Also there is another certlint: GlobalSign's certlint (written in Go). I haven't tried that.

Pubkey generator identification

Also: There is some research on how to detect the library used to generate RSA pubkeys: From Usenix Sec 2016: The Million-Key Question—Investigating the Origins of RSA Public Keys (Archived here.)

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