It is possible to use SSH to encrypt the network connection between clients and a PostgreSQL server. Done properly, this provides an adequately secure network connection, even for non-SSL-capable clients.
   First make sure that an SSH server is
   running properly on the same machine as the
   PostgreSQL server and that you can log in using
   ssh as some user;  you then can establish a
   secure tunnel to the remote server.  A secure tunnel listens on a
   local port and forwards all traffic to a port on the remote machine.
   Traffic sent to the remote port can arrive on its
   localhost address, or different bind
   address if desired;  it does not appear as coming from your
   local machine.  This command creates a secure tunnel from the client
   machine to the remote machine foo.com:
ssh -L 63333:localhost:5432 joe@foo.com
   The first number in the -L argument, 63333, is the
   local port number of the tunnel; it can be any unused port.  (IANA
   reserves ports 49152 through 65535 for private use.)  The name or IP
   address after this is the remote bind address you are connecting to,
   i.e., localhost, which is the default.  The second
   number, 5432, is the remote end of the tunnel, e.g., the port number
   your database server is using.  In order to connect to the database
   server using this tunnel, you connect to port 63333 on the local
   machine:
psql -h localhost -p 63333 postgres
   To the database server it will then look as though you are
   user joe on host foo.com
   connecting to the localhost bind address, and it
   will use whatever authentication procedure was configured for
   connections by that user to that bind address.  Note that the server will not
   think the connection is SSL-encrypted, since in fact it is not
   encrypted between the
   SSH server and the
   PostgreSQL server.  This should not pose any
   extra security risk because they are on the same machine.
  
   In order for the
   tunnel setup to succeed you must be allowed to connect via
   ssh as joe@foo.com, just
   as if you had attempted to use ssh to create a
   terminal session.
  
You could also have set up port forwarding as
ssh -L 63333:foo.com:5432 joe@foo.com
   but then the database server will see the connection as coming in
   on its foo.com bind address, which is not opened by
   the default setting listen_addresses =
   'localhost'.  This is usually not what you want.
  
If you have to “hop” to the database server via some login host, one possible setup could look like this:
ssh -L 63333:db.foo.com:5432 joe@shell.foo.com
   Note that this way the connection
   from shell.foo.com
   to db.foo.com will not be encrypted by the SSH
   tunnel.
   SSH offers quite a few configuration possibilities when the network
   is restricted in various ways.  Please refer to the SSH
   documentation for details.
  
Several other applications exist that can provide secure tunnels using a procedure similar in concept to the one just described.