On 2012-05-27 at 00:19 -0400, Phil Pennock wrote:
> This is strange.  Exim should have been using a file named
> "gnutls-params-2236", for the number of bits in the file.
> 
> Oh crap.  I know what it is.  GnuTLS generates *approximately* the
> number of bits requested, and can go over.  OpenSSL is more exact, but
> takes significantly longer.
> 
> Crap crap crap.  I'll lower the default value of tls_dh_max_bits, so
> that even when generation goes over, the count will *probably* only be
> 2236 and NSS will work.
> 
> You probably had a 2237 bit key in the file.

I spent some time trying to find an API call to interrogate the size so
we could retry until the value was acceptable.  I failed to find one.

I've mailed the GnuTLS mailing-list, suggesting such a call might be
Quite Useful.

There is no sane way I can find to hook into get the value, except
perhaps another debug hook which extracts data from the text string
passed in.

So, first pass, I subtracted 3 from the tls_dh_max_bits, to request
2233.  In my first test, the generated DH prime had 2240 bits.

We now subtract 10, if tls_dh_max_bits is at least 1034.

We're still using a strategy called "hope".  This is Not Good (tm).

-Phil

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