Used ISDN and had the fax machine plugged into the encryption box and that into the ISDN wall socket. Though no reason why such an approach could be utilised f

Used ISDN and had the fax machine plugged into the encryption box and that into the ISDN wall socket. Though no reason why such an approach could be utilised for pots based FAX machines. As for the encryption - was pre-shared key type affair and unable to elaborate further.