[gnutls-dev] Re: Feature request: not really random session keys

[Florian Weimer]

* Simon Josefsson:

> Florian Weimer <fw at deneb.enyo.de> writes:
>
>> I tracked this down to the generation of the RSA_EXPORT key.  In this
>> case, bits from /dev/random are used, even though the generated key is
>> horribly insecure anyway.
>>
>> Wouldn't it make sense to use only STRONG_RANDOM in this case, and not
>> VERY_STRONG_RANDOM?
>
> Perhaps.  But doesn't this happen for non-RSA_EXPORT keys too?  We
> wouldn't want to make that change there.

I think you'd need to pass an additional flag, yes.  It's certainly
not a two-line change, and I can understand if you don't want to make
it for such a silly feature.

> It seems better to fix Exim here.

Even if we follow the advice in your other message, a busy mail server
will deplete the pool at an alarming rate (each TLS-enabled SMTP
connection consumes 600 bytes from the kernel pool -- which can only
store 4096 bits).  This means that gathering the required true
randomness may take a long time.  We'll see if it's still acceptable,
or if the randomness is distributed so unfairly that it won't work.