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If i want to use client certificates for authentication to a certain part of my website, is it possible to make the client certificate only work on a certain domain name?

I know when requesting the client certificate you can request the CA. But i want it so if my site is domain.com and the client visits a fake website domainn.com then when the client certificate is requested on that fake website it will be impossible for the real client certificate to be used as it wont match to the correct domain.

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    What's your concern with cert reuse? – Neil Smithline May 22 '18 at 3:20
  • Would fake website domainn.com be any less convincing if it does not retrieves the client certificate? – curiousguy May 24 '18 at 9:16
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You can't regulate where the cert goes as it's handled by the client (browser in your case). There's nothing in a client cert to restrict it to specific domains. The browser is free to send it wherever it wishes. There are settings in the browser that lets users control where the certs go, but that too is out of your control.

That said, I'm not sure why you care who gets the cert. If you're using client certs, there's no chance of phishing or MiTMing.

  • do you know of any documents that go into detail of how phishing is not possible? – PixelPaul May 22 '18 at 23:49
  • Phishing attacks credentials - passwords and sometimes OTPs (eg: Google Authenticator). When you're using client certs, you generally don't have passwords. If you're using passwords with client certs as a 2FA, then phishing would be possible, though the user would likely get a browser popup asking them to select the cert for the website. And they still wouldn't get the cert's private key as that is never transmitted. So it is safe against all but browser vulnerabilities and malware installed on the computer. – Neil Smithline May 23 '18 at 15:00
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    What are you concerned that will be phished? – Neil Smithline May 23 '18 at 15:01
  • Phishing is always "possible", it's a user issue: as long as a user is willing to enter data in a form in a random website, and able to connect to that website (not possible if you're on an intranet with only access to a few white listed legit domains), and able to remember that secret code (not possible if you don't remember the code and have a browser autofill feature that only works on a given domain), phishing is possible. – curiousguy May 24 '18 at 9:14
  • @curiousguy I'm not sure how phishing is possible if mutual auth SSL is the only authentication in use,. What would be phisbed? The private key? Seems unlikely to me. – Neil Smithline May 25 '18 at 2:50

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