3 ms·

As far as I know, X.509 doesn't currently have such a concept, and web browsers don't have it either. If you install a certificate as a CA, it is a CA for any

As far as I know, X.509 doesn't currently have such a concept, and web browsers don't have it either. If you install a certificate as a CA, it is a CA for any domain. If a CA signs another certificate with the "Certificate Sign" flag (intermediate certificate), that other certificate is also a CA for any domain. The subject name fields are not used when validating authority as a CA.

pabs3 5y ago
Well, there is the name constraints mechanism, but I'm not sure how well supported that is in TLS libraries and web browsers. https://datatracker.ietf.org/doc/html/rfc5280#section-4.2.1.10 https://datatracker.ietf.org/doc/html/rfc5280#section-4.2.1.... https://timothy-quinn.com/name-constraints-in-x509-certificates/ https://timothy-quinn.com/name-constraints-in-x509-certifica... https://www.sysadmins.lv/blog-en/x509-name-constraints-certificate-extension-all-you-should-know.aspx https://www.sysadmins.lv/blog-en/x509-name-constraints-certi... https://blog.codekills.net/2012/04/08/adventures-in-x509-the-utterly-ignored-nameconstraints/ https://blog.codekills.net/2012/04/08/adventures-in-x509-the...
- maxdamantus 5y ago
  Thanks, I wasn't aware of that. I guess I'd feel a bit more comfortable installing a CA with those constraints, though I'd wonder how many administrators actually know to do it—seems like a feature that's not currently well known and something that can be easily overlooked. There would also be risks to users if installing these custom CAs became common practice. It might be safe to do it for certificates with suitable name constraints, but until certificate installation UIs add something special for this ("this certificate has authority over X, Y, Z"), users aren't going to distinguish between safe/unsafe (constrained/unconstrained) CAs.
- btown 5y ago
  They seem decently well supported, see e.g. https://nameconstraints.bettertls.com/#!view?results=chrome_63_osx10.13.3 https://nameconstraints.bettertls.com/#!view?results=chrome_... and https://nameconstraints.bettertls.com/#!view?results=firefox_50_windows https://nameconstraints.bettertls.com/#!view?results=firefox...
  - tialaramex 5y ago
    However, note that some relatively modern versions of Safari (because of course) don't support this constraint. This might be no problem for you, or, it might be a complete showstopper.
jesboat 5y ago
It does; they're called "name constraints". This page https://systemoverlord.com/2020/06/14/private-ca-with-x-509-name-constraints.html https://systemoverlord.com/2020/06/14/private-ca-with-x-509-... claims they're supported by "all current browsers". x509 extensions can be marked "critical" or not. If the name constraint was marked critical, then AIUI old software should (in theory) fail secure, and reject everything signed by the CA.

pabs3 5y ago

Well, there is the name constraints mechanism, but I'm not sure how well supported that is in TLS libraries and web browsers. https://datatracker.ietf.org/doc/html/rfc5280#section-4.2.1.10 https://datatracker.ietf.org/doc/html/rfc5280#section-4.2.1.... https://timothy-quinn.com/name-constraints-in-x509-certificates/ https://timothy-quinn.com/name-constraints-in-x509-certifica... https://www.sysadmins.lv/blog-en/x509-name-constraints-certificate-extension-all-you-should-know.aspx https://www.sysadmins.lv/blog-en/x509-name-constraints-certi... https://blog.codekills.net/2012/04/08/adventures-in-x509-the-utterly-ignored-nameconstraints/ https://blog.codekills.net/2012/04/08/adventures-in-x509-the...

maxdamantus 5y ago
Thanks, I wasn't aware of that. I guess I'd feel a bit more comfortable installing a CA with those constraints, though I'd wonder how many administrators actually know to do it—seems like a feature that's not currently well known and something that can be easily overlooked. There would also be risks to users if installing these custom CAs became common practice. It might be safe to do it for certificates with suitable name constraints, but until certificate installation UIs add something special for this ("this certificate has authority over X, Y, Z"), users aren't going to distinguish between safe/unsafe (constrained/unconstrained) CAs.
btown 5y ago
They seem decently well supported, see e.g. https://nameconstraints.bettertls.com/#!view?results=chrome_63_osx10.13.3 https://nameconstraints.bettertls.com/#!view?results=chrome_... and https://nameconstraints.bettertls.com/#!view?results=firefox_50_windows https://nameconstraints.bettertls.com/#!view?results=firefox...
- tialaramex 5y ago
  However, note that some relatively modern versions of Safari (because of course) don't support this constraint. This might be no problem for you, or, it might be a complete showstopper.

jesboat 5y ago

It does; they're called "name constraints". This page https://systemoverlord.com/2020/06/14/private-ca-with-x-509-name-constraints.html https://systemoverlord.com/2020/06/14/private-ca-with-x-509-... claims they're supported by "all current browsers". x509 extensions can be marked "critical" or not. If the name constraint was marked critical, then AIUI old software should (in theory) fail secure, and reject everything signed by the CA.