[openssl-users] How to get list of TLS protocols supported by OpenSSL?

[Jakob Bohm]

On 13/11/2015 03:56, pratyush parimal wrote:
> Hi,
>
> I'm writing a client-server program that uses TLS for communication.
> I'm wondering if there's any way to programmatically find out which 
> TLS protocol versions are supported by the OpenSSL library installed 
> on my system.
>
> I'm currently aware of three ways which "sort of" provide this 
> information:
> (1) After setting up the TLS communication, call: 
> SSL_get_version(ssl);  which returns "TLSV1.2", etc.
> (2) Try to connect to a server using TLS by specifying all possible 
> TLS versions in the client program, and see which connections pass/fail.
> (3) Call: SSL_get_ciphers(), print their names, and try to correlate 
> them with the protocol they're associated with.
>
> Unfortunately, none of the above answer my question completely.
>
> So is it possible to ascertain which TLS protocol versions are 
> actually supported by my server-program, without trying the above 
> methods? My purpose is not to simply make a list for my own reference, 
> but rather finding it out on-the-fly in the server-side program, since 
> I may run it on different versions of OpenSSL.
>

If  there is no suitable direct API, the following might
still be helpful:

(4) Get the OpenSSL library version directly and compare
   to the known version ranges supporting different SSL/TLS
   versions.
(5) Looking for ways to determine the configure options
   used when the SSL library was built (in particular if it
   was compiled without some SSL/TLS versions supported in
   the source code of that version).

Enjoy

Jakob
-- 
Jakob Bohm, CIO, Partner, WiseMo A/S.  https://www.wisemo.com
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