One can 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. Then you can establish a secure tunnel with a command like this from the client machine:
ssh -L 3333:foo.com:5432 [email protected]
The first number in the -L argument, 3333, is the port number of your end of the tunnel; it can be chosen freely. The second number, 5432, is the remote end of the tunnel: the port number your server is using. The name or IP address between the port numbers is the host with the database server you are going to connect to. In order to connect to the database server using this tunnel, you connect to port 3333 on the local machine:
psql -h localhost -p 3333 postgres
To the database server it will then look as though you are really user [email protected] and it will use whatever authentication procedure was configured for connections from this user and host. 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 as long as they are on the same machine.
In order for the tunnel setup to succeed you must be allowed to connect via ssh as [email protected], just as if you had attempted to use ssh to set up a terminal session.
Tip: Several other applications exist that can provide secure tunnels using a procedure similar in concept to the one just described.