Re: Client Certificate Verification

> On Dec 17, 2023, at 12:13, John Levine <johnl@iecc.com> wrote:
> 
> It appears that Doug Hardie <bc979@lafn.org <mailto:bc979@lafn.org>> said:
>> -=-=-=-=-=-
>> 
>> I have an application to which clients connect using a browser over SSL.  I have a LetsEncrypt certificate for the app that lets the client authenticate the app. 
>> However, I need to have a multitude of client certificates (one per client machine).  I am generating these certificates from a self-signed root certificate.  I can get
>> the client to verify the app and provide the client certificate to it.  The app is unable to verify the client certificate.  I have not been able to figure out how to
>> have openssl distribute one certificate (from LetsEncrytp), but verify the received client certificate using different certificate chain.  Openssl will pass me some of
>> the received certificate fields.  However, without certificate verification I cannot be sure that those values came from a certificate I generated.  Is there a way to do
>> this either with openssl or libtls?
> 
> OpenSSL gets its list of trusted root signers from a big list in
> /etc/ssl so you want to add your CA to that list. See the certctl
> command for more details on how it's managed.
> 
> Most FreeBSD systems use the ca_root_nss package to update that list,
> so the trick is to keep your cert from getting deleted the next time
> the package is updated. You might try putting your cert in
> /usr/local/share/certs/ rather than /usr/share/certs/trusted where the
> standard certs are.

Finally got some time to work on this again.  That approach works very well.  My client certificates are properly accepted.  However, I am unable to tell just what SSL_accept validates.  I have not been able to find any documentation on what it actually checks.  My testing shows that the client certificate must be signed by a known root certificate, but does SSL_accept verify that the signing certificate is the one indicated in the client certificate, and how does it check that?  In my server, I am checking the certificate serial number.  The subject CN is being used to send the real user id.   Is that necessary and sufficient to ensure that the certificate is the one I generated and not a fake?

 It seems that it might be possible to create a CA that is certified by one of the known root certificates and use it to generate a client certificate with the identical issuer information.  Obtaining the proper issuer serial number would take some work, but I suspect it is possible.  The rest of that information is trivial.  Thanks,

-- Doug