Re: [PATCH] apache: generating unique prime numbers and forbit use of weak DH cipher suites

[IT Superhack <itsuperhack@web.de>]

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Michael Tremer:
> On Thu, 2015-06-04 at 21:48 +0200, IT Superhack wrote:
>> Hello Michael,
>>
>> Michael Tremer:
>>> Hi,
>>>
>>> On Wed, 2015-06-03 at 10:27 +0200, IT Superhack wrote:
>>>> Hello Michael,
>>>>
>>>> I tested a bit in the last hours. There were a few issues I discovered
>>>> and I had to change my patch.
>>>>
>>>> First, the prime number generation is much slower than I expected - it
>>>> took up to 20 minutes on my system. (I guess I had a lucky moment when I
>>>> wrote the last mail to you...)
>>>
>>> That is a no-go then. The key will be generated when the system boots up
>>> for the first time. Nobody will wait half an hour until that has
>>> completed. We always prefer security over usability but it must still be
>>> possible to set up a fresh system within minutes.
>> I expected this answer and completly agree with you. If a user has to
>> wait 1-2 minutes, fine. But 20 minutes are way too much.
>>>
>>> I am not opposed to the idea in general. In fact I would like to use an
>>> own DH key for each system as this patch suggests, but the solution must
>>> be less interruptive to the user.
>> Hm, I'm afraid the solution of this won't be very easy, but I'm going to
>> think about it.
>>>
>>>> Second, Apache seems to ignore the DH prime numbers. On
>>>> https://weakdh.org/sysadmin.html it says that Apache 2.4.8 or newer is
>>>> required for the "SSLOpenSSLConfCmd" option.
>>>>
>>>> I have therefore decided to switch DH off, and use ECDHE only, which is
>>>> more safe and - by the way - faster than DH. This is not a problem,
>>>> because modern browsers support ECDHE, except for some exotic clients
>>>> such as Android 2.3.7 and Java Client 6u45.
>>>
>>> We can definitely not use only ECDHE. Many OSes do not support elliptic
>>> curve cryptography not only because of their age but often because of
>>> patents.
>> Oh yes, I forgot.
>>>
>>> RedHat still disables all ECC in openssl for all their distributions.
>> Could you update Apache to 2.4.8 or newer? Then the "SSLOpenSSLConfCmd"
>> would be supported and _this_ part of the problem would be solved.
> 
> For a start we could update apache and add a script that adds the DH
> params. In that way the security-aware users can execute the script,
> wait for an hour or so and then can use their own key.
That is a good idea. We can just use a version of "httpscert", which
would have an extra option, maybe "gendhparams" or something similar for
generating DH prime numbers.

However, as you already said, this is not a permanent solution. Many
systems will be unprotected since their owners don't have the time to
run the script. We need something fast and maybe automated here, without
annoying the user.

How about this scenario:
You (= the developers) ship a script with the next update. This script
generates DH primes in background and then modifies the apache config
file so it uses the DH primes after they have been successfully created.
This way, the user would not be blocked; the generation could also take
place at night, when usually nothing important else happens.

This would be also an idea for the installation. Only the HTTPS certs
are generated on the first boot, the DH prime can be created later or at
the users request. If some DH prime is present, a script updates the
apache config file.
> 
> That way we can also get some more experience about how long the whole
> process takes and where potential problems are.
Provided that some people would like to share their results with us,
this would be nice.
> 
> Apache has not been updated in recent time because the release we are
> currently using is still supported. But there is no reason why we should
> not try an update, either. Will you have a go at that?
I'm not sure what you're meaning with your last sentence (bad english,
sorry :-) ), but i can take care about this issue.
> 
>>>> And yes, you were right: The DES-suites were ignored. Please see the new
>>>> cipher list in the patch below. In my opinion, the patch is now ready
>>>> for merging, unless you have someting against it.
>>>>
>>>> Signed-off-by: Timmothy Wilson <itsuperhack(a)web.de>
>>>> ---
>>>> diff --git a/config/httpd/vhosts.d/ipfire-interface-ssl.conf
>>>> b/config/httpd/vhosts.d/ipfire-interface-ssl.conf
>>>> index daac757..a8bbae7 100644
>>>> --- a/config/httpd/vhosts.d/ipfire-interface-ssl.conf
>>>> +++ b/config/httpd/vhosts.d/ipfire-interface-ssl.conf
>>>> @@ -9,7 +9,7 @@
>>>>      TransferLog /var/log/httpd/access_log
>>>>      SSLEngine on
>>>>      SSLProtocol all -SSLv2 -SSLv3
>>>> -    SSLCipherSuite
>>>> ECDHE-RSA-AES128-GCM-SHA256:ECDHE-ECDSA-AES128-GCM-SHA256:ECDHE-RSA-AES256-GCM-SHA384:ECDHE-ECDSA-AES256-GCM-SHA384:DHE-RSA-AES128-GCM-SHA256:DHE-DSS-AES128-GCM-SHA256:kEDH+AESGCM:ECDHE-RSA-AES128-SHA256:ECDHE-ECDSA-AES128-SHA256:ECDHE-RSA-AES128-SHA:ECDHE-ECDSA-AES128-SHA:ECDHE-RSA-AES256-SHA384:ECDHE-ECDSA-AES256-SHA384:ECDHE-RSA-AES256-SHA:ECDHE-ECDSA-AES256-SHA:DHE-RSA-AES128-SHA256:DHE-RSA-AES128-SHA:DHE-DSS-AES128-SHA256:DHE-RSA-AES256-SHA256:DHE-DSS-AES256-SHA:DHE-RSA-AES256-SHA:AES128-GCM-SHA256:AES256-GCM-SHA384:AES128:AES256:HIGH:!RC4:!aNULL:!eNULL:!EXPORT:!DES:!3DES:!MD5:!PSK
>>>> +    SSLCipherSuite
>>>> ECDHE-RSA-AES128-GCM-SHA256:ECDHE-ECDSA-AES128-GCM-SHA256:ECDHE-RSA-AES256-GCM-SHA384:ECDHE-ECDSA-AES256-GCM-SHA384:DHE-RSA-AES128-GCM-SHA256:DHE-DSS-AES128-GCM-SHA256:kEDH+AESGCM:ECDHE-RSA-AES128-SHA256:ECDHE-ECDSA-AES128-SHA256:ECDHE-RSA-AES128-SHA:ECDHE-ECDSA-AES128-SHA:ECDHE-RSA-AES256-SHA384:ECDHE-ECDSA-AES256-SHA384:ECDHE-RSA-AES256-SHA:ECDHE-ECDSA-AES256-SHA:AES128-GCM-SHA256:AES256-GCM-SHA384:AES128-SHA256:AES256-SHA256:CAMELLIA:HIGH:!DH:!LOW:!aNULL:!eNULL:!EXPORT:!3DES:!DES:!RC4:!MD5:!PSK:!aECDH
>>>>      SSLHonorCipherOrder on
>>>>      SSLCertificateFile /etc/httpd/server.crt
>>>>      SSLCertificateKeyFile /etc/httpd/server.key
>>>
>>>> Sorry for my harsh words in my last mail about pseudonyms and this stuff.
>>>
>>> No worries.
>>>
>>>>
>>>> Best regards,
>>>> Timmothy Wilson
>>>
>>> -Michael
>>>
>> So, to sum it up, there are two things to do:
>> 1: Find a way so generating DH group doesn't block the user for hours
>> 2: Find a way to use DH "safe" for legacy clients (might be solved by
>> updating Apache)
>>
>> Best regards,
>> Timmothy Wilson
>>
>>
> 
> -Michael
> 
Best regards,
Timmothy Wilson



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