[squid-users] ssl_bump with intermediate CA

[Amos Jeffries]

On 2017-01-06 21:27, senor wrote:
> Thank you for the response but I think my question is still unanswered.
> Comments below:
> 
> On 1/5/2017 16:57, Bruce Rosenberg wrote:
>> The cafile option specifies the "chain" file squid should send back to
>> the client along with the cert, exactly as you would normally do with
>> Apache httpd or Nginx.
> (For clarity: I'm using 3.5.23. cafile was replaced in squid-4)
> This may be what cafile is used for but that does not match the
> directive description.
> http://www.squid-cache.org/Versions/v3/3.5/cfgman/http_port.html
> My suspicion is that the description is a confusion between the same
> option in openssl and web server options (Apache SSLCACertificateFile
> and similar).
> What's it really used for? Chain completion, client cert verification 
> or
> both?

It is used for chain completion. *which* chain is being completed 
depends on the traffic mode.

clientca= should be the one used *only* for client cert verification (I 
think). But neither was used consistently in Squid-3, so YMMV based on 
the traffic modes.

> 
>> In the example the generated server cert is depth 0, CA2 is depth 1 
>> and
>> CA1 is depth 2.
>> If the client has CA1 installed as a trust anchor then technically you
>> don't need to send CA1 as it is discarded by the client once the trust
>> relationship for CA2 is established.
>> It's good practice to send the full chain though as it makes
>> troubleshooting easier.
>> From a client perspective you can quickly grab the whole chain with
>> openssl s_client and check if CA1 is in the trust store.
> I have to disagree with this. The anchor (CA1) is discarded regardless.
> It cannot be used. If included it bloats the TLS handshake. Even 
> openssl
> will discard it and then look in the trusted CA store.
> 
> I see with a packet cap that the mimicked server cert and the signing
> cert are both included even without the cafile option specified.
> 
> So is it safe to say that the referenced wiki page has just become
> outdated? If cafile is used to fill in the cert chain it wouldn't be
> needed unless there were additional intermediate certs between the mitm
> cert and the trusted CA known to the client. (As in CA1 is trusted by
> clients, CA1 signs CA2 which signs CA3 which is used as MITM cert,
> cafile=CA2)

That wiki page was incorrect at the time of creation. But the author 
refuses to agree that root cert are discarded so I left it there instead 
of inciting an edit war. Saving the root CA into the file should be 
harmless anyway.

Amos