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Re: [saag] subordinate vs intermediate certification authority

Michael Richardson <mcr+ietf@sandelman.ca> Thu, 04 February 2021 17:13 UTC

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From: Michael Richardson <mcr+ietf@sandelman.ca>
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Date: Thu, 04 Feb 2021 12:13:22 -0500
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Subject: Re: [saag] subordinate vs intermediate certification authority
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Viktor Dukhovni <ietf-dane@dukhovni.org> wrote:
    > On Wed, Feb 03, 2021 at 11:10:43PM -0500, Michael Richardson wrote:

    >> I thought I had cross-posted this, but apparently I did not:
    >>
    >> https://mailarchive.ietf.org/arch/msg/anima/3tNwWb9gBacdYMTr1TtXzSa_3_Q/
    >>
    >> RFC5280 uses the term "intermediate certificates", and they are
    >> RFC4949 defines "intermediate CA" RFC4949 defines "subordinate CA" in
    >> a way that implies it is part of the same RFC5280 uses the term
    >> "subordinate" in section 3.2, but later in referring to
    >>
    >> At this point, in 2020, can someone give me some guidance on using
    >> these terms?

    > FWIW, in the context of OpenSSL, Postfix, etc., I see/use the terms
    > "root CA certificate", "intermediate CA certificate" and "end-entity
    > certificate".  Where "root CA certificates" are self-signed,
    > "end-entity certificates" are the certificates of the peer, and
    > everything in between is just intermediate certificates.

    > From a verifier perspective there is little reason to make distictions
    > on a more granular level.

Yes, I agree that there is no important distinction from a chain validation
point of view.

    >> However, if the Anchor (level N) and the Level N+1 certification
    >> authority are in different organizations (such as for an "Enterprise
    >> Certificate"), then the Level N+1 is a subordinate CA.

    > Again, from the vantage point of the verifier, there's no practical way
    > to know.  Some of the Let's Encrypt CA certs are issued by DST others
    > by ISRG.  In common usage, I typically see these referred to as
    > intermediate certificates, but e.g. the ISRG CPS appears to prefer
    > "subordinate":

That seems to be consistent with my hypothesis that the term "subordinate"
represents a split in administrative authority.

    > So as I see it, "intermediate" and "subordinate" are essentially
    > synonymous, with some technical communities using the former and others
    > the latter to mean basically the same thing.


--
Michael Richardson <mcr+IETF@sandelman.ca>   . o O ( IPv6 IøT consulting )
           Sandelman Software Works Inc, Ottawa and Worldwide

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