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Comment by jameshart

11 years ago

There's no such thing in X509 as a cert which is authorized only to sign certs within a certain subdomain. A CA is either trusted or not; if it's trusted, it can sign off on a cert for www.google.com.

A system where there's a .com root cert that can sign authority certs for .com subdomains, which themselves can only sign for their own subdomains - that's a great idea. Not part of the standard, though.

8 comments

jameshart

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pzb  11 years ago

There is such a thing -- name constraints. It allows exactly what you describe, limiting the valid names for certificates signed by the certificate.

  • jameshart  11 years ago

    Interesting - that's news to me, and does allow a domain-registry-based hierarchy. I guess there's the old revocation-check problem, though - when someone transfers a domain or it expires, you'd need to be able to revoke the authority cert. Potentially leads to a lot of revocation checks to validate a cert chain correctly...

    • h4xar  11 years ago

      You mention that the revocation-check problem is old, which is certainly true, but I think you allude to the possibility that a domain-registry-based hierarchy will exacerbate that problem in the form of an increase in revocation checks. I'm not sure that would be the case; it should be about the same. What difference does it make if I owned a domain, got a cert from a CA, and stopped owning the domain -- vs -- got that cert from my registrar? If anything this helps the process, because my registrar knows when I stop owning the domain whereas a CA has no clue and relies on the cert's expiration date exclusively.

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  • jessaustin  11 years ago

    I think this is kind of backwards? I.e. a CA that implements name constraints for one of its sub-CAs does limit the certs that sub-CA may sign. However, name constraints do not allow one to say "for this domain, only this sub-CA may sign certs", which is more what I feel we're looking for here?

darkarmani  11 years ago

> There's no such thing in X509 as a cert which is authorized only to sign certs within a certain subdomain. A CA is either trusted or not; if it's trusted, it can sign off on a cert for www.google.com.

As currently implemented this is mostly correct. I don't think the CAs want that situation to change, but it really harms the usability of the entire system.