FREAK/Logjam, and SSL protocols to use

Gedalya gedalya at
Wed May 27 15:35:09 UTC 2015

On 05/27/2015 09:55 AM, Rick Romero wrote:
>  Quoting Gedalya <gedalya at>:
>> On 05/26/2015 10:37 AM, Ron Leach wrote:
>>> includes altering DH parameters length to 2048, and re-specifying the
>>> allowable cipher suites - they give their suggestion.
>> It looks like there is an error on this page regarding regeneration. In
>> current dovecots ssl_parameters_regenerate defaults to zero, and this
>> means regeneration is disabled. The old default was 168 hours (1 week).
>> The language on is
>> confusing and could be understood to mean that the current default is
>> one week.
>> To enable regeneration you can manually set:
>> ssl_parameters_regenerate = 60 days
>> or:ssl_parameters_regenerate = 1 weeks
> This is really cool and all, but for a low power proxy, it takes a good 5
> minutes to regenerate the dh params, and Dovecot listens the entire time.
> If the socket were closed during regeneration, then a (basic) front-end
> load balancer wouldn't still push connections to that proxy during regen.
> Rick

I wonder if what is taking 5 minutes is CPU usage or entropy starvation. 
Might be worth looking into.

However the entire reason why I wrote this comment was to correct the 
mistaken line saying "#regenerates every week". It is not at this point 
emphasized anywhere, including on, that it is actually of 
high importance to regenerate your DH parameters frequently. This has 
been discussed extensively e.g. within the exim project and other 
places, and on dovecot too the default was changed to not regenerate. It 
seems that people are mostly just saying you should have locally 
generated parameters unique to your site.

But to address your point, if this feature is deemed worth maintaining, 
it seems it would be best to spawn a thread working on the new 
parameters in the background and replacing them when ready.

Otherwise dovecot can just implement a dh_parameters config option like 
all other daemons and you can maintain that externally as you please. 
But we're supposed to be focusing on EC anyway :-)

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