Can a linux service work as both TLS client and server?

Kristen Webb kwebb at
Fri Nov 15 22:10:55 UTC 2019

Is there a way for a single program to act as both a TLS client and a TLS
server after a TCP/IP accept() call?

Today, I simply have the TCP connecting process issue a 1 or 0 to indicate
how it is acting.  This is then used to determine who does SSL_accept and
SSL_connect and everything works out.  My original idea was that I could
then configure any number of supporting services on the same port going

I'd like to remove this 1 time TCP write/read operation. For example, I
cannot see how this will work with Apple's network framework going forward.

I currently have 3 authentication use cases

      Server side cert (currently only works in one direction without my
      Server side cert with GSSAPI (currently only works in one direction
without my workaround)
      Client/Server certs (so this one should work either way)

Will PSK allow my service to say, always act as a TLS server without a
server certificate?
Could I then proceed with additional certificate functions (e.g. for

Or should I go back and grovel for another port and use this information to
explain why I need one?

Many thanks in advance for any insights!

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Mr. Kristen J. Webb
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