[pkix] Self-issued certificates

Peter Bowen <pzbowen@gmail.com> Sun, 12 July 2015 22:02 UTC

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Date: Sun, 12 Jul 2015 15:02:53 -0700
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From: Peter Bowen <pzbowen@gmail.com>
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Subject: [pkix] Self-issued certificates
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I'm trying to make sense of the definition of "self-issued
certificates" in RFC 5280 (and X.509)

Section 3.2 provides a definition: "Self-issued certificates are CA
certificates in which the issuer and subject are the same entity."
However section 6.1 says "A certificate is self-issued if the same DN
appears in the subject and issuer fields."

While it is clear that all certificates with the same DN for subject
and issue are self-issued, it is unclear to me whether a certificate
with different DNs could be self-issued.  Section 6.1 could be giving
one example of how a certificate could be self-issued or section 6.1
could be a limiting definition.

Consider the following example:
Example Trust Services has two different private keys.  Each key has a
single associated DN:
Key0 has DN O=Example Trust Services, OU=Global Trust Anchor
Key1 has DN O=Example Trust Services, OU=Commercial Trust Anchor

There is a CA certificate created with
Subject: O=Example Trust Services, OU=Commercial Trust Anchor
Subject Public Key: Key1
Issuer: O=Example Trust Services, OU=Global Trust Anchor
Signed by Key0

Is this CA certificate considered a self-issued certificate?

Thanks,
Peter