On Tue, Apr 24, 2001 at 12:27:28PM +0200, Peter Lindsäth wrote:
> I have the following certificates:
>
> root.cert - self signed CA
> node1root.cert - issued by root
> node2root.cert - issued by root
> daemon.cert - issued by node1root
> client1.cert - issued by node2root
>
> I have an SSL server which use the daaemon.cert and has root.cert and node1.cert
> in its certificateChain.
> I want to accept and authenticate clients issued by node2root. Not all
> 'children' to root.cert.
>
> My question is what do I put in SSL_CTX_add_client_CA() to make my CA list, and
> what should I put in the file SSL_CTX_load_verify_locations() loads?
Disclaimer: I haven't tested any of the following ideas!
1 You put node2root.cert into SSL_CTX_add_client_CA(). Therefore you advertise
that you trust node2root.cert. (You could also add root.cert instead, it
must be filtered out in step 3 anyway.)
2 You put root.cert to SSL_CTX_load_verify_locations(). When a client
certificate is presented, it will undergo the complete check of the
OpenSSL library including certificate purpose etc. If it fails in any
regard, further checks can be omitted anyway.
(When the root cert is not found, the error message appearing will depend
on the certificate chain sent (with/without root cert), so catching this
special condition may be difficult. Also, the certificate chain verification
has been carefully crafted by Steve Henson and I would rather trust this
verificatin routine and only later apply an additional check than
trying to hack something together myself.)
3 After establishing the connection, you call SSL_get_peer_cert_chain()
and examine the chain. If node2root.cert is not part of the chain
(use X509_cmp() to compare certificates), close the connection immediately
and remove the session, as it became invalid.
3a Step 3 can be modified in a way, that the verification already takes place
in the verify_callback. If you always know for sure, that node2root.cert
is issued by root.cert (level 1), you can check at level 1 whether
node2root.cert is matched and flag failure if not. This may however
become tricky later when you change your structure and want to change
your CA structure. You have forgotten about this special restriction
(level 1 checking) and spend weeks finding out why it fails with
your new structure...
Therefore the corresponding checks in verify_callback() must be
carefully crafted to be flexible enough. Maybe set a flag when the
"trusted" CA was found at any level and then on the last level, when
OK is found, check whether the "trusted" flag is set and only then
let the OK pass and change to "fail" otherwise....
I personally would tend to version 3a on the long run...
Best regards,
Lutz
--
Lutz Jaenicke [EMAIL PROTECTED]
BTU Cottbus http://www.aet.TU-Cottbus.DE/personen/jaenicke/
Lehrstuhl Allgemeine Elektrotechnik Tel. +49 355 69-4129
Universitaetsplatz 3-4, D-03044 Cottbus Fax. +49 355 69-4153
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