Moving SSL connections between processes (was: Question)

Dmitry Belyavsky beldmit at
Mon Aug 14 15:57:50 UTC 2023

Dear Victor,

On Mon, Aug 14, 2023 at 5:52 PM Viktor Dukhovni <openssl-users at>

> On Thu, Aug 10, 2023 at 03:56:31PM +0000, Mohammad Zolfaghari wrote:
> > Openssl documentation explicitly says "SSL_set_session() is only
> > useful for TLS/SSL clients" while we are transferring the session on
> > the server side from one process to the another. Do you still think
> > that using the session on the server side can prevent us from
> > duplicating the key agreement phase?
> The above is not very clear, but I'm guessing you're talking about TLS
> session resumption across processes.  Yes, this possible, by
> implementing external session cache callbacks (as e.g. in Postfix where
> multiple SMTP server processes consult a common session cache maintained
> by the tlsmgr(8) helper process).
> This requires the client to perform a second handshake, either over a
> new connection, or after performing a two-way TLS shutdown on the
> existing socket, and starting a fresh handshake, with, presumably at
> that point, the second server process.
> Note that in TLS 1.3 session resumption still in practice performs a DH
> key exchange in most cases, you just get to avoid signing the key
> exchange.  You can, in principle arrange to configure only psk_ke (and
> not psk_dhe_ke) on both ends, and then get a resumption without the cost
> of a fresh DH key exchange, but this only works with coöperating
> clients.  Importantly, *all* clients then need to be happy to do psk_ke,
> or else you get handshake failures.
> You're wading into the deep end of the pool, perhaps you should stick
> with more simple solutions.

If it is the project I am thinking about (, it's not the case. The
idea is that we have a long process on the server side that would be
terminated in case of dropping the connection.

I believe that the proper solution is altering the server so the
transaction here will be in the background and reconnection with some extra
id of transaction will allow some sort of attaching to the process, but it
also is not so simple.

SY, Dmitry Belyavsky
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