On Fri, Feb 01, 2013 at 03:22:11PM +0000, Viktor Dukhovni wrote:
> On Fri, Feb 01, 2013 at 01:46:46PM +0000, Nathan Smyth wrote:
>
> > Is it possible to have null, untrusted, or shared certificates,
> > to simplify deployment for apps that don't care about SSL?
>
> Absolutely. On all servers that don't require client certificates
> (can't ask for client certs when using an anonymous ciphersuite)
> enable anonymous ciphers, using an appropriate configuration
> parameter that invokes SSL_CTX_set_cipher_list(). A sensible cipher
> list for OpenSSL 1.x is:
>
> aNULL:-aNULL:ALL:!EXPORT:!LOW:!SSLv2:@STRENGTH
>
One more thing, since anonymous ciphers do ephemeral Diffie-Hellman
ephemeral Elliptic Curve DH key exchange, you must provide ECDHE
and EDH callbacks in the server code to select a prime/generator
(g = 2 as a rule) pair for DH, or a named curve for EC.
This also gives you forward secrecy even with certificates, so
you should have these in either case.
DH:
See documentation for SSL_CTX_set_tmp_dh_callback()
EC:
if ((nid = OBJ_sn2nid(curve)) == NID_undef)
/* error unsupported curve */
if ((ecdh = EC_KEY_new_by_curve_name(nid)) == 0
|| SSL_CTX_set_tmp_ecdh(server_ctx, ecdh) == 0)
/* some other error */
--
Viktor.
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