SSL Server setup DH/ECDH

[Matt Caswell]

On 06/08/2019 11:21, Chitrang Srivastava wrote:
> Yes , since in my case mostly browser will be used to access webserver running
> on embedded platform.
> Another question, since my webserver is running on embedded platform and it has
> limited memory , I have disabled
> ARIA/CAMELLIA  and few others, is that OK ? because I don't see any ciphers
> suites which is used in practice.

Yes, that should be fine.

Matt

> 
> 
> 
> On Tue, Aug 6, 2019 at 3:42 PM Matt Caswell <matt at openssl.org
> <mailto:matt at openssl.org>> wrote:
> 
> 
> 
>     On 06/08/2019 11:07, Chitrang Srivastava wrote:
>     > Thanks Matt,
>     >
>     > So now I have, which i believe is enough ?
>     >
>     > SSL_CTX_set_options(s_ctx,  SSL_OP_NO_RENEGOTIATION |
>     > SSL_OP_CIPHER_SERVER_PREFERENCE);
>     > SSL_CTX_set_min_proto_version(s_ctx, TLS1_2_VERSION);
> 
>     This is fine although it obviously prevents connections from very old clients
>     that don't support TLSv1.2. This might not be a problem for you depending on
>     your situation.
> 
>     Matt
> 
>     >
>     > On Tue, Aug 6, 2019 at 3:04 PM Matt Caswell <matt at openssl.org
>     <mailto:matt at openssl.org>
>     > <mailto:matt at openssl.org <mailto:matt at openssl.org>>> wrote:
>     >
>     >
>     >
>     >     On 06/08/2019 09:42, Chitrang Srivastava wrote:
>     >     > Hi,
>     >     >
>     >     > I am implementing HTTPs server using openssl 1.1.1b.
>     >     > Is it mandatory to setup these API's while creating ssl context ?
>     >     >
>     >     > SSL_CTX_set_tmp_ecdh
>     >     >
>     >     > SSL_CTX_set_tmp_dh
>     >
>     >     By default OpenSSL will automatically use ECDH if appropriate and choose a
>     >     suitable group so there is no need to call SSL_CTX_set_tmp_ecdh()
>     unless you
>     >     want more control over which specific group is used.
>     >
>     >     OpenSSL will not use DH unless you specifically configure it. If you
>     want to
>     >     make use of DH based ciphersuites then you must either call
>     SSL_CTX_set_tmp_dh()
>     >     or SSL_CTX_set_dh_auto() (or the SSL_* equivalents). Calling the
>     former enables
>     >     you to configure any arbitrary DH group that you choose. Calling the
>     latter will
>     >     enable the built-in DH groups.
>     >
>     >     It is not mandatory to call any of the above.
>     >
>     >     >
>     >     > Also any suggestion what all options one should set while setting up
>     >     server like
>     >     > SSL_CTX_set_options like SSL_OP_NO_SSLv2 |SSL_OP_NO_SSLv3
>     >
>     >     Don't use the protocol version specific options at all. Use
>     >     SSL_CTX_set_min_proto_version() if you want to specify a minimum protocol
>     >     version. SSLv2 is no longer supported at all. SSLv3 is compiled out by
>     default.
>     >
>     >     Other options that are worth considering are SSL_OP_NO_RENEGOTIATION and
>     >     (possibly) SSL_OP_CIPHER_SERVER_PREFERENCE. Generally you don't need
>     the others
>     >     unless there is a specific problem you are trying to solve.
>     >
>     >     Matt
>     >
>