The most interesting part of Keryx is that you can install or upgrade the package for your Ubuntu or Debian system from another Linux or Windows system which got better Internet connection.
Go to the Keryx website and click the download link. Once the download is complete, unzip it and put the entire folder on a USB pen drive that has a decent amount of free space.
To run the application, go to folder where you have extracted the Keryx (Keryx_Ubuntu_x86/linux) and execute the file : keryx_linux_32bit
On start of Keryx application, it will ask you to create the project which is nothing but the snapshot of your offline system, it will also download few files to prepare the repository.
Now when you take this project (USB drive) to some other system (Linux / MAC or Windows) and execute the keyrx (linux/keryx on Linux,or win32/keryx.exe on Windows) the Keryx application will start emulating the update by using the information from its project, Now, in the end you have all the packages, with resolved dependencies, on a pen-drive. Just plug it into your offline system and install them.
If you want to install any new application, just search for that particular application using the search bar on the Keryx, select it, right click on it and then choose 'Download’. The package(s) will be downloaded to your device and later you can install it on your offline Ubuntu system.