[openssl-users] SSL version status

Karl Denninger karl at denninger.net
Thu Jan 28 16:49:54 UTC 2016

On 1/27/2016 07:56, Nulik Nol wrote:
> Hi,
> I have to implement SSL/TLS in a proprietary web server daemon. I am
> only familiar with SSL as a user, not as developer, so my question is.
> What versions of SSL should I support for best compatibility and
> optimal development time? How much old browsers are out there that
> still use older SSL versions? Because, Wikipedia says SSL 3.0 was
> deprecated by Jun 2015 but if I only implement TLS, I may lose many
> visitors with old browsers, right ?
> Please advise.
> Nulik
Some, to use a single word.  Not many though.

The notable problems come from very old mobile handsets (e.g. Froyo and
similar Android). I have about 3% of my users on systems I manage still
hitting them from XP machines as an example of "old", which are
potential issues in this regard, BUT TLS1.0 is supportable by XP -- so
shutting off SSL3 won't kill those users.

There are a smattering of machines that still hit my sites running
Windows 98, however (well under 1%), believe it or not.

Be aware that the OpenSSL defaults when you define a server context are
inappropriate for most purposes and thus you have to do a bit more work
when programming a server to get a reasonably-secure environment than
when connecting using OpenSSL as a client.  Specifically, be aware of
issues surrounding client renegotiation requests (which can turn into a
denial-of-service problem) and how you handle Diffie-Hellman (if you
choose to load said keys) along with the ECDH cipher set.  For a server
you also have to consider whether you're going to multiplex or
multithread as OpenSSL requires some additional attention at the
programming level (for locking) in a threaded application.

Karl Denninger
karl at denninger.net <mailto:karl at denninger.net>
/The Market Ticker/
/[S/MIME encrypted email preferred]/
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