oeSENC Plugin for OpenCPN provides support for encrypted OCPN Vector Charts. These are licensed and sourced from chart providers like Hydrographic Offices. These - non free - charts must be installed with appropriate encryption certificates in place. Chart source o-charts.org
Please Note: This plugin requires OpenCPN version 4.6 or higher.
For Ubuntu Linux and it's derivatives (Linux Mint) and Debian Jessie based distributions, OpenCPN is distributed from a PPA. If you're not sure how to add the repository to your system, read the chapter Configuring Ubuntu PPA in the user manual.