At the bottom of https://tools.ietf.org/html/rfc5280#page-12 and
top of https://tools.ietf.org/html/rfc5280#page-13 (last paragraph
of above https://tools.ietf.org/html/rfc5280#section-3.3), we see:
This specification covers two classes of certificates: CA
certificates and end entity certificates. CA certificates may be
further divided into three classes: cross-certificates, self-issued
certificates, and self-signed certificates. Cross-certificates are
CA certificates in which the issuer and subject are different
entities. Cross-certificates describe a trust relationship between
the two CAs. Self-issued certificates are CA certificates in which
the issuer and subject are the same entity. Self-issued certificates
are generated to support changes in policy or operations. Self-
signed certificates are self-issued certificates where the digital
signature may be verified by the public key bound into the
certificate. Self-signed certificates are used to convey a public
key for use to begin certification paths. End entity certificates
are issued to subjects that are not authorized to issue certificates.
that the term "self-issued" is only applicable to CAs, not end-entity
certificates. In https://tools.ietf.org/html/rfc5280#section-4.2.1.9
the description of path length constraints says:
The pathLenConstraint field is meaningful only if the cA boolean is
asserted and the key usage extension, if present, asserts the
keyCertSign bit (Section 4.2.1.3). In this case, it gives the
maximum number of non-self-issued intermediate certificates that may
follow this certificate in a valid certification path. (Note: The
last certificate in the certification path is not an intermediate
certificate, and is not included in this limit. Usually, the last
certificate is an end entity certificate, but it can be a CA
certificate.)
This makes it clear that exclusion of self-issued certificates from
the path length count applies only to some *intermediate* CA
certificates. A leaf certificate whether it has identical issuer
and subject or whether it is a CA or not is never part of the
intermediate certificate count. The handling of all leaf certificates
must be the same, in the case of our code to post-increment the
path count by 1, so that we ultimately reach a non-self-issued
intermediate it will be the first one (not zeroth) in the chain
of intermediates.
Reviewed-by: Matt Caswell <matt@openssl.org>
(cherry picked from commit ed422a2d01)
bb6923945e