[Dovecot] force ciphers order for clients

Robert Schetterer rs at sys4.de
Wed Aug 14 23:04:00 EEST 2013

Am 14.08.2013 21:30, schrieb Reindl Harald:
> Am 14.08.2013 21:19, schrieb Robert Schetterer:
>>>> thx Harald, upgrading openssl to 1.x and using dove 2.2.5 is no option
>>>> at my setup lucid ubuntu yeter
>>> so you can practically forget it
>> perhaps true forever, as long old clients are around, cause the server
>> can only workaround them
> not absolutely
> playing around with the setings below and https://www.ssllabs.com/ssltest/
> turned out that the order is what counts, and that is really tricky
> i played around 5 hours with this absoluetly crap

that sounds good, so you allready did many real world tests

> adding !MEDIUM results in open from CRIME or BEAST attack because
> some clients chosse a vulerable cipher, but it would raise up the
> overall points of the test BUT at the same time perfect forward
> secrecry for most clients while with settings below only
> for Apple iOS/Safari
> without the -SHA1 also vulernable for one of the new attacks
> sorry, i refused to notice what and tried ot achive best possible
> encryption while not fall back to classification B what is important
> for security audits
> BEAST attack is unlikely in context mail
> IMHO this is all bullshit currently *but* if recent clients start
> to act smarter they can choose the best possible cipher offered
> from the server and after that you have your copmpatibility net
> for old clients - currently this all is a tragedy, but having
> PRISM/NSA and the latest news about in mind most likely recent
> clients will be able to choose a "perfect forward secrecy"
> capable cipher if offered by the server independent of weaker ones
> the real problem in your case will most likely be that most
> of the shiny new things in this area will require recent
> openssl and TLS1.2 (sadly not supproted by Mozilla/NSS for now)

i will upgrade openssl and whole setup as soon as possible, meanwhile
looking for best working tmp solution

> ________________________________________________________________________________________________
> SSLProtocol All -SSLv2 -SSLv3
> SSLCompression Off
> SSLInsecureRenegotiation Off
> SSLHonorCipherOrder On
> SSLCipherSuite

i have a testing setup with newer openssl/dove i will try your settings
with a few clients there, but that will take time going on vacation soon


Best Regards
MfG Robert Schetterer

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