On 03.07.2012 08:11, Alex Rousskov wrote:
Hello,
Awaken by DigiNotar CA compromise, various web agents now try
harder
to validate SSL certificates (see 2011 squid-dev thread titled "SSL
Bump
Certificate Blacklist" for a good intro). From user point of view, a
bumping Squid is the ultimate authority on server certificate
validation, so we need to go beyond basic OpenSSL checks as well.
Various protocols and other validation approaches are floating
around:
CRLs, OCSP, SCVP, DNSSEC DANE, SSL Notaries, etc. There is no
apparent
winner at the moment so we are in a stage of local experimentation
through trial-and-error. We have seriously considered implementing
one
of the above mentioned approaches in Squid, but it looks like it
would
be better to add support for a general validation helper instead, so
that admins can experiment with different approaches.
The helper will be optionally consulted after a successful internal
OpenSSL validation we do now. It will receive the origin server
certificate [chain] and the intended domain name. On errors, the
helper
will return the validation error name (see %err_name error page macro
and %err_details logformat code), error reason (%ssl_lib_error
macro),
and possibly the offending certificate (%ssl_subject and %ssl_ca_name
macros) -- similar to what the internal validation code returns now.
Squid may maintain a cache of certificate validation results to
reduce
validation performance burden (indexed by certificate fingerprint?).
On this point. If you are using the helper API you will be wanting to
have a helper result cache. These are keyed on the input string sent to
the helper.
Squid will provide a dummy helper. Eventually, full-featured helpers
may
be contributed (but I am currently not planning on writing one).
If there are no objections, I would like to detail the above on Squid
wiki and eventually submit a patch implementing this feature in v3.3.
Do
you think that is a good idea?
I think it would be good to provide the extra flexibility.
I am in the process of modifying the helper API for consistency across
all helpers starting with 3.3. It would be great if you could design
your helper to use a generic output format for data sent back to Squid:
[channel-ID] (OK/ERR/BH) [key-pairs] <terminator>
* With BH optionally as a broken-helper failure state as per the NTLM
helper API.
* Noticing how there are *no* fixed-position fields beyond the result
code.
For data from Squid to helper please design with minimum number of
fixed-position/type fields and define [key-pair] as optional
extension(s) to hold whatever data is optionally sent to the helper.
Ideally we will never transmit any fields which could be "-"/"[unknown]"
to or from the helper.
Amos
