Bug#560690: gnutls26: Handle client certificate files with included ca certificates more gracefully

[Friedrich Delgado Friedrichs]

Package: gnutls26
Severity: wishlist

Hi!

It hased caused me much confusion that gnutls does not handle client
certificates well, if they contain ca certificates together with the
client cert and key (at least that seems to be the case if the ca
certificate are listed *before* the client cert).

(You can see much of the resulting confusion as well as the discovery
of the real cause in
http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=530510 )

In particular,
,----
  gnutls-cli --print-cert --verbose -p 4711 --x509certfile \
    /home/user/secret/organisation-user.pem -p 443 \
    intern.organisation.org \
    --x509keyfile /home/user/secret/organisation-user.pem
`----

Fails with a key usage violation error if organisation-user.pem
contains the ca certificates before the client cert.

Unfortunately, some CAs generate client certs like this (i.e. first
key, then the certs in order of the chain, i.e. first the root-ca and
client-ca certs, then the client cert) and firefox and openssl export
them in the same order. Also openssl handles that case gracefully.

The pkcs12 manpage (from openssl) even states:

,----[ manual page pkcs12(1) ]

       If none of the -clcerts, -cacerts or -nocerts options are
       present then all certificates will be output in the order
       they appear in the input PKCS#12 files. There is no
       guarantee that the first certificate present is the one
       corresponding to the private key. Certain software which
       requires a private key and certificate and assumes the first
       certificate in the file is the one corresponding to the
       private key: this may not always be the case. Using the
       -clcerts option will solve this problem by only outputting
       the certificate corresponding to the private key. If the CA
       certificates are required then they can be output to a
       separate file using the -nokeys -cacerts options to just
       output CA certificates.
`----

Which was quite helpful once I discovered why it didn't work.

Unfortunately I could not find any reference to this behaviour in the
gnutls documentation. Also the error message "key usage violation
error" doesn't help a lot.

(http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=530510 documents we
looked at the key usage bits in the client and server certs first,
which were all correct.)

In order of preference, I'd like one or all of the following resolutions:

 - If the certificate doesn't fit the key, try another one in the same
   file.

 - "key usage violation error" could output some information about
   which certificate it actually tried to use. (Which would give a
   hint that it tried to use a CA cert.)

 - Document in a prominent place that gnutls does not support
   client certificate files with CA certificates in them. (Sorry if I
   simply overlooked it.)

Should 530510 be closed or merged with this wishlist bug?

Kind regards
     Friedel
-- System Information:
Debian Release: squeeze/sid
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  APT policy: (990, 'testing'), (500, 'unstable'), (500, 'stable'), (1, 'experimental')
Architecture: amd64 (x86_64)

Kernel: Linux 2.6.30-2-amd64 (SMP w/1 CPU core)
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