nginx and ephemeral Diffie-Hellman keys

[Igor Sysoev]

On Sat, Jun 14, 2008 at 08:09:13AM +0400, Igor Sysoev wrote:

> On Fri, Jun 13, 2008 at 11:13:37PM +0200, Jauder Ho wrote:
> 
> > Patch applied and testing now.
> > 
> > >From reading the patch, it looks like the key is generated once. I did 
> 
> No, not key itself but DH parameters, those will be used to generate DH keys.
> 
> > some more digging and reference 
> > http://mail-archives.apache.org/mod_mbox/httpd-cvs/200205.mbox/%3C20020530181716.22766.qmail@icarus.apache.org%3E
> > 
> > Key should be changed out every so often.
> > 
> >   - o Diffie-Hellman-Parameters for temporary keys are hardcoded in
> >   -   ssl_engine_dh.c, while the comment in ssl_engine_kernel.c says:
> >   -   "it is suggested that keys be changed daily or every 500
> >   -    transactions, and more often if possible."
> 
> Nevertheless Apache still uses hardcoded DH parameters and does not allow
> to override them.

Looking in Apache repo: modern DH params in Apache/2 are 3 years old,
Apache's 1.3 DH params are 9 years old.

It's seems thare is no need to override them using ssl_dhparam.

> Actually both nginx and Apache use SSL_CTX_set_options(SSL_OP_SINGLE_DH_USE)
> and OpenSSL generate new DH key during the negotiation.
> 
> BTW, while RSA-only case the only keys used in negotiation are
> server certificate keys, those are not changed one year.


-- 
Igor Sysoev
http://sysoev.ru/en/