The umbrella term Security in Signal K server refers to the difference between running an unsecured server, that everybody who has network access to it can access and alter at will, and a secured server that has one or more security restrictions enabled.

The security options are related to

• authentication: the users are authenticated, for example but not limited to username & password
• access control: based on authentication we can grant / limit access to Signal K data and server configuration
• secure communications: is the network traffic protected against eavesdropping by using encryption and can the identity of the server be verified
• active network services: which of the server's services/interfaces are configured and active, for example does it allow unsecured read/write over the network

You can tell that a server does not have security turned on from not having Login option at the top right corner of the admin UI.

You can enable security in several ways:

• by accessing the Security settings pages in the admin UI
• starting the server with the --securityenabled option
• adding the following section in the settings file

"security": {
    "strategy": "./tokensecurity",
  }

When security is enabled the admin UI will prompt you to create the admin account in the admin UI.

Security configuration is stored in file called security.json which will be located in the configuration directory.

In case you accidentally lose your admin credentials you can remove security.json and restart.

Access control lists allow fine grained control of access to specific data in SignalK. The acls are a list which allow specifiying controls for specifc contexts and it goes in the security.json file mentioned above.

The following example defines acls for the self context. It allows anyone to read the paths "steering.*", "navigation.*", "name", "design.aisShipType" and allows the admin user permission to write (update) those paths.

The second entry allows the user john to read any data coming from the actisense.35 $source.

The last entry covers all other paths, allowing only the admin user to read and no one can write.

If there is no match is found for a specific path in the acl list, then permission will be denied to that path.

  "acls": [
    {
      "context": "vessels.self",
      "resources": [
        {
          "paths": ["steering.*", "navigation.*", "name", "design.aisShipType"],
          "permissions": [
            {
              "subject": "any",
              "permission": "read"
            },
            {
              "subject": "admin",
              "permission": "write"
            }
          ]
        },
        {
          "sources": [ "actisense.35" ],
          "permissions": [
            {
              "subject": "john",
              "permission": "read"
            }
          ]
        },
        {
          "paths": ["*"],
          "permissions": [
            {
              "subject": "admin",
              "permission": "read"
            }
          ]
        }
      ]
    }
  ]

Signal K server's main networks services are

• the primary Signal K http / WebSocket interface, with options to use TLS encryption and authentication (read/write)
• NMEA0183 data over TCP on port 10110 (read only)
• Signal K over TCP on port 8375 (read/write)

In addition the user may configure any number of TCP, UDP and Websocket connections, some of which allow write access to the server.

The security implication of these connections is that with no security options turned on computers that have network access to the server have both read and write access to practically all of its data and settings.

People often dismiss local network access by saying that their boat's local network is secure enough. But one very common scenario is connecting your SK server, for example a Raspberry Pi, as a client to a marina wifi. Many wifi networks allow communication between all connected computers. Your the server will be advertising its services over MDNS to all other connected computers. If there is a manually configured connection for NMEA0183 over UDP other computers broadcasting data can easily write data to the server.

NMEA0183 connections over TCP and UDP are inherently unsafe: there are no options for authentication and secure communication. In comparison Signal K over TLS and HTTP / WebSockets can provide secure, authentication read and write access to your data.