dovecot - Feb 2015 - TLS config check

According to https://cipherli.st/
> ssl = yes
> ssl_cert = </etc/dovecot.cert
> ssl_key = </etc/dovecot.key
> ssl_protocols = !SSLv2 !SSLv3
> ssl_cipher_list = AES128+EECDH:AES128+EDH
> ssl_prefer_server_ciphers = yes # >Dovecot 2.2.6
> Is what you want.
Ok, so I have changed my ssl_cipher_list to: ssl_cipher_list = 
AES128+EECDH:AES128+EDH

Before I made this change clients were connecting with the following 
cipher in the log file:

ECDHE-ECDSA-AES256-SHA (256/256 bits)

After the change the log now says:

ECDHE-ECDSA-AES128-GCM-SHA256 (128/128 bits)

Is this an improvement (or more secure) despite going from 256bits to 
128bits?

Thanks!

Am 06.02.2015 um 23:13 schrieb SW:
>   According to https://cipherli.st/
>> ssl = yes
>> ssl_cert = </etc/dovecot.cert
>> ssl_key = </etc/dovecot.key
>> ssl_protocols = !SSLv2 !SSLv3
>> ssl_cipher_list = AES128+EECDH:AES128+EDH
>> ssl_prefer_server_ciphers = yes # >Dovecot 2.2.6
>> Is what you want.
>
> Ok, so I have changed my ssl_cipher_list to: ssl_cipher_list >
AES128+EECDH:AES128+EDH
>
> Before I made this change clients were connecting with the following
> cipher in the log file:
>
> ECDHE-ECDSA-AES256-SHA (256/256 bits)
>
> After the change the log now says:
>
> ECDHE-ECDSA-AES128-GCM-SHA256 (128/128 bits)
>
> Is this an improvement (or more secure) despite going from 256bits to
> 128bits?
yes it is because AES-GCM is currently the best cipher suite while there 
is no point for AES256, if AES128 will fall then it likely affects 
AES256 too and according to Brcue Schneier years ago AES128 has even 
less problems then AES256 (too lazy for google it again)

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Am 07.02.2015 um 04:47 schrieb Reindl Harald:
> 
> Am 06.02.2015 um 23:13 schrieb SW:
>>   According to https://cipherli.st/
>>> ssl = yes
>>> ssl_cert = </etc/dovecot.cert
>>> ssl_key = </etc/dovecot.key
>>> ssl_protocols = !SSLv2 !SSLv3
>>> ssl_cipher_list = AES128+EECDH:AES128+EDH
>>> ssl_prefer_server_ciphers = yes # >Dovecot 2.2.6
>>> Is what you want.
>>
>> Ok, so I have changed my ssl_cipher_list to: ssl_cipher_list >>
AES128+EECDH:AES128+EDH
>>
>> Before I made this change clients were connecting with the following
>> cipher in the log file:
>>
>> ECDHE-ECDSA-AES256-SHA (256/256 bits)
>>
>> After the change the log now says:
>>
>> ECDHE-ECDSA-AES128-GCM-SHA256 (128/128 bits)
>>
>> Is this an improvement (or more secure) despite going from 256bits to
>> 128bits?
> 
> yes it is because AES-GCM is currently the best cipher suite while there
> is no point for AES256, if AES128 will fall then it likely affects
> AES256 too and according to Brcue Schneier years ago AES128 has even
> less problems then AES256 (too lazy for google it again)
> 
Well, I am working in the crypto field and was a bit astonished about
this "rant" - so a quick search brought up
https://www.schneier.com/blog/archives/2009/07/another_new_aes.html -
for those who want it more compact
http://crypto.stackexchange.com/questions/5118/is-aes-256-weaker-than-192-and-128-bit-versions.

Bottom line: AES256 *IS* better than AES128 for the intended usage but
it is also true that AES-GCM rules out other AES based block ciphers for
other kinds of attacks, so there is no "black or white" answer. To be
honest, I wont worry on this - people who are in the position to break
even a 128bit key will most likely find other ways to get into your mail
communication ;)

Oliver

-- 
Protect your environment -  close windows and adopt a penguin!

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