Feature req: DH prime bitsize query

[Nikos Mavrogiannopoulos]

On 05/27/2012 10:47 AM, Janne Snabb wrote:

> On Sun, 27 May 2012, Phil Pennock wrote:
> 
>> When gnutls_dh_params_generate2() is used to generate DH parameters of a
>> particular size, it has a tendency to overshoot.
>>
>> Asking for 2236 bits, a 2237 bit prime seems to be fairly common.
> 
> Ouch!
> 
>> Could GnuTLS 3 *please* get an API call to find out the size in bits of
>> the DH prime in a gnutls_dh_params_t ?  Perhaps even add a query mode to
>> certtool?
> 
> New version of certtool prints out the number of bits. Are you looking
> for this:
> 
> $ certtool --dh-info --infile=/var/spool/exim4/gnutls-params-2236
> Generator (8 bits): 02
> 
> Prime (2240 bits):
>         0f:00:55:99:82:cb:c0:eb:42:eb:ef:33
> [..]


That number is an overestimation. It is the number of bytes in the
number times 8, thus a function that returns a more precise number would
improve this aspect as well.

regards,
Nikos