Whew, that was a long title! Hi, folks. I'm a Fedora QA person who's been poking at SSL stuff as a sort of sideline lately; please don't give me too much credit for my email address, I'm not one of RH's official security / SSL folks, so please be gentle when I'm wrong ;) This is all with OpenSSL 1.0.1k on Fedora Rawhide. Lately I've been trying to figure out if it's possible / desirable to switch to using the OpenSSL 'trusted certificate' format (the one whose PEM-encoded certificates have 'BEGIN TRUSTED CERTIFICATE' rather than 'BEGIN CERTIFICATE') for a distribution's trust store. The case I'm (currently) interested in is what exactly happens if you try to distrust a CA using the 'trusted certificate' system. To this end, I've been doing some tests. I'm using the certificate chain that's used by my personal domain (https://www.happyassassin.net ), so it should be quite easy to reproduce. My certificate is a StartCom level 2 cert; the root CA cert is http://www.startssl.com/certs/ca.pem and the intermediate CA cert is http://www.startssl.com/certs/sub.class2.server.ca.pem , my server certificate is attached for convenience or can easily be retrieved from...the server. I'm using Fedora's p11-kit-based trust store generation system. If I put ca.pem in /etc/pki/ca-trust/source/blacklist , run `update-ca- trust` and then `trust extract --format=openssl-directory --filter blacklist black` , what p11-kit does is generate a 'TRUSTED CERTIFICATE' format certificate file named StartCom_Certification_Authority.pem for the blacklisted CA and place it in the directory 'black' (if you actually try this you'll also get a few other files in there, for CAs that are blacklisted by system policy). (The '--filter blacklist' stops it also generating files for all the trusted CAs, just to keep things clean). It also generates the necessary hash symlinks for OpenSSL to treat the directory as a CApath, of course. If you run `openssl x509 -in black/StartCom_Certification_Authority.pem -noout -text`, you see how p11-kit tries to use the 'TRUSTED CERTIFICATE' extensions to indicate that the CA should not be trusted: No Trusted Uses. Rejected Uses: TLS Web Server Authentication, TLS Web Client Authentication, Code Signing, E-mail Protection, IPSec End System, IPSec Tunnel, IPSec User, Time Stamping So, hopefully that picture's clear? The intent is that if you use black/ as the CApath for validation, certs issued by that CA should not be trusted. For comparison, I have the directory white/ , which contains p11-kit's output for the same CA when whitelisted / trusted: Trusted Uses: E-mail Protection, TLS Web Server Authentication, Code Signing No Rejected Uses. In one of my test cases, this seems to work pretty well. I just try to connect to my server with s_client, using the two different CApaths. black: [adamw at adam tmp]$ openssl s_client -CApath black/ -connect www.happyassassin.net:443 ... verify error:num=28:certificate rejected verify return:0 ... Verify return code: 28 (certificate rejected) white: [adamw at adam tmp]$ openssl s_client -CApath white/ -connect www.happyassassin.net:443 ... verify return:1 ... Verify return code: 0 (ok) However, if I use 'openssl verify' (and provide the intermediate cert with -untrusted), it doesn't work as expected. No errors occur, even with the 'black' CApath. [adamw at adam tmp]$ openssl verify -CApath black/ -untrusted sub.class2.server.ca.pem www.happyassassin.net.crt www.happyassassin.net.crt: OK Even if I pass a purpose: [adamw at adam tmp]$ openssl verify -purpose sslserver -CApath black/ -untrusted sub.class2.server.ca.pem www.happyassassin.net.crt www.happyassassin.net.crt: OK The outputs of `openssl x509 -in white/StartCom_Certification_Authority.pem -noout -purpose` and `openssl x509 -in black/StartCom_Certification_Authority.pem -noout - purpose` are identical. I've been staring at the code and docs for this for several hours to try and figure out what the difference between the 'verify' and 's_client' paths is, and I finally had to sort of throw up my hands and admit defeat, and come and ask for help :) It seems to me that it must be the case, somehow, that on the 'openssl verify' path the root certificate just isn't run through X509_check_trust(). But I can't see why not. To my idiot eyes, verify.c's check() and ssl_cert.c's ssl_verify_cert_chain() look like they do more or less the same thing, and verify.c's verify_callback doesn't seem to suppress any errors. After a lot of searching I did satisfy myself that anything that goes through ssl3_connect() gets a default purpose and trust (it had been suggested on the RH bug that only consumers which explicitly set these would get one), but that doesn't explain why 'openssl verify' works even with a -purpose. If anyone can point out what I'm missing I'd be very grateful :) As well as my server cert I'll attach the 'black' and 'white' .pem files and the intermediate cert. -- Adam Williamson Fedora QA Community Monkey IRC: adamw | Twitter: AdamW_Fedora | XMPP: adamw AT happyassassin . net http://www.happyassassin.net -------------- next part -------------- A non-text attachment was scrubbed... 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