Le 02/07/2012 10:34, Johannes Bauer a écrit :
I have a rather simple question regarding X.509 subjects that is not
entirely clear to me and for which I cannot find the appropriate
reference (pointers greatly appreciated). The trouble starts when trying
to compare two subjects of *different* certificates for equality and
becomes worse when certain fields are appearing more than once. To
clarify, by "equal" I mean 'should behave in exactly the same way by all
well-behaved implementations.
Let's start easy. Consider the following subjects:
subject1= /C=SE/O=FooBar/OU=BarFoo/CN=moo.koo.com
subject2= /C=SE/OU=BarFoo/CN=moo.koo.com/O=FooBar
Are these to be considered equal or not?
Not equal.
I.e.: Does the order of
elements matter? Does the order matter when fields are duplicate, i.e. are:
The order of elements in a SEQUENCE matters. The order of elements in a
SET doesn't matter (read X.690 to get DER rules).
Comparison rules for AttributeAndValue elements follow X.520
recommendation (you have to canonicalize them before comparison).
subject1= /CN=foo/CN=bar
subject2= /CN=bar/CN=foo
equal?
Not equal.
If they are not equal, does the first one have a special meaning? For
example, assume a webserver with a duplicate common name field. Are both
names valid as the server name then? I.e. could I access a webserver
with the certificate subject as stated above by DNS "foo" *and* "bar" or
only by one of them?
This is not specified by X.509. Browsers tend to accept such a
certificate for an accessed FQDN equal to either "foo" or "bar". But you
SHOULD place at most the first FQDN in a CN element in the subject, and
other FQDN values in the subjectAlternativeName extension.
One reason to ask for equality is that there maybe is a certificate X:
issuerX = /O=myCA/OU=greatCA/CN=not
subjectX= /CN=foo/CN=bar
and it has a valid signature by a CA with the following subject:
issuerX = /OU=greatCA/O=myCA/CN=not
Is the certificate signature then valid?
The signature may be cryptographically valid, but the names don't match,
so "/OU=greatCA/O=myCA/CN=not" is not the issuer of "/CN=foo/CN=bar" (at
least not in what you described, "/CN=foo/CN=bar" may have another
certificate).
--
Erwann ABALEA
-----
Pas de panique, ça sera pire.
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