To install Dukto in Ubuntu then follow these commands. These commands are perfectly working in Ubuntu 12, Ubuntu 16.04 and Ubuntu 18.
sudo apt-get install gdebi sudo wget download.opensuse.org/repositories/home:/colomboem/xUbuntu_12.04/amd64/dukto_6.0-1_amd64.deb sudo gdebi dukto_6.0-1_amd64.deb
After installing this you need to disable the firewall also for perfectly working. Please note disabling firewall only if you have a knowledge of firewall and its security features otherwise add its TCP protocol to firewall allowed list.