Kerberos DSL-Configurable Burglar Alarm System

Kerberos is a highly-flexible burglar alarm system for the Raspberry Pi. It is configurable through a domain-specific language and arbitrary C functions. It was originally designed and implemented to run under FreeBSD using the pbio(4) 8255 parallel peripheral interface basic I/O driver, with an interface such as the Advantech PCL-724 Digital I/O Card. It was later modified to run on a Raspberry Pi with the Wiring Pi API. In both cases a custom-built PCB interfaces the alarm system to passive infrared (PIR), magnetic, and other sensors as well as to actuators, such as sirens.

Note that configuring and deploying Kerberos requires significant hardware, programming, security, and system administration skills. The code and documentation provided here, is just to get you started, it is by no means a turnkey solution.

Configuration

To configure Kerberos pick a name for your configuration, say acme, and create three files.

• acme-io.h specifies the Kerberos's sensors and actuators.
• acme.alr specifies the Kerberos's rules as state transitions. For example, it can specify that in the armed state a movement in the bedroom will make it enter the intruder state and sound a siren.
• acme-cmd.h specifies the names of Kerberos's user commands (e.g. disarm).

One set of simple and one set of more sophisticated example files are provided, but the possibilities of what you can do are limitless. Here are some ideas.

• Kerberos can send notifications using cellular SMS, a voice modem, web push notifications, or email.
• Kerberos can filter-out spurious movements.
• Kerberos can warn you through a home appliance, such as Alexa, before it raises hell in the neighborhood.
• Kerberos can automatically disarm based on IoT signals.
• Kerberos can be operated and monitored through a web interface or a phone app.
• Kerberos can automatically enter diverse states at specific times through cron(8) jobs.
• Kerberos can enter diverse states based on movement patterns.

A Note on Safety and Security

Although setting up Kerberos may appear to be a fun hobby project, note that the safety of yourself, your loved ones, and your property may end up depending on it. Moreover, spurious alarms can distress your neighbours and get you into trouble with law enforcement authorities. (In some countries a spurious alarm call to the police results in a steep fine.) Finally consider that the Kerberos's operation may face determined opponents who may use any possible means, including physical force and violence, to neuter it. Consequently, you need to carefully verify and validate your setup and your operations. This includes careful design and planning, exhaustive testing, and also training of the people who will be using the system. In your design think about the Kerberos's physical access control, backup power and communications links, watchdog monitoring, and tamper alarms. If your system running Kerberos will be accessible over the internet, you need to harden it against intrusions and denial of service attacks.

Pay special attention to the following two sections of the Kerberos's license agreement.

15. Disclaimer of Warranty.

THERE IS NO WARRANTY FOR THE PROGRAM, TO THE EXTENT PERMITTED BY APPLICABLE LAW. EXCEPT WHEN OTHERWISE STATED IN WRITING THE COPYRIGHT HOLDERS AND/OR OTHER PARTIES PROVIDE THE PROGRAM "AS IS" WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. THE ENTIRE RISK AS TO THE QUALITY AND PERFORMANCE OF THE PROGRAM IS WITH YOU. SHOULD THE PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF ALL NECESSARY SERVICING, REPAIR OR CORRECTION.

16. Limitation of Liability.

IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MODIFIES AND/OR CONVEYS THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES, INCLUDING ANY GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED TO LOSS OF DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU OR THIRD PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER PROGRAMS), EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES.

Building and Deployment

• Download, build, and install the WiringPi API.
• Build the system by running make.
• Install the generated alarm daemon and command-line interface by running sudo make install.
• Configure logging so as to monitor Kerberos's operation. Here is an example configuration for rsyslogd(8), which you could place in /etc/rsyslog.d/alarm.conf.

# Administrative information
if $programname == 'alarm' and $syslogseverity-text == 'info' then /var/log/alarm.log

# Exhaustive alarm sensor logging (included in debug messages)
if $programname == 'alarm' then /var/log/radar.log

# Discard information and debug so that they don't go anywhere else
# (Does not work with rsyslogd 5.8.11
#if $syslogseverity >= 6 and $programname == 'alarm' then ~

# Discard all alarm messages
if $programname == 'alarm' then ~

• Configure alarm log rotation. Here is an example of a logrotate(8) configuration file, which you could place in /etc/logrotate.d/alarm.

/var/log/radar.log {
        daily
        rotate 22000
        olddir archive/radar
        dateext
        dateyesterday
        missingok
        compress
        delaycompress
        sharedscripts
        postrotate
                invoke-rc.d rsyslog rotate > /dev/null
        endscript
}

/var/log/alarm.log {
        monthly
        rotate 1200
        olddir archive/alarm
        dateext
        dateformat "-%Y%m"
        dateyesterday
        missingok
        compress
        delaycompress
        sharedscripts
        postrotate
                invoke-rc.d rsyslog rotate > /dev/null
        endscript
}

• Kerberos runs as a service named alarm through an installed initd script. Enable the service to run at startup and start it up.
• Create the following directories: * /var/spool/alarm/cmd/: communication between the command-line interface alarm and the daemon. * /var/spool/alarm/disable/: names of manually disabled sensors * /var/spool/alarm/sensor/: sensor trigger counts * /var/spool/alarm/status/: Kerberos's status
• You send commands to the daemon through the command-line alarm program. This creates files in the /var/spool/alarm/cmd/ directory. Configure the directory's permissions and have cmd run with the appropriate permissions (e.g. through sudo(1) or by having alarm run with setuid permissions), so that this scheme will work securely.

Operation

In the form provided you operate Kerberos with the alarm command, which accepts the commands that you configured. You monitor Kerberos's operation through the configured log files, e.g. with tail -F /var/log/radar.log. You will most probably want to setup a more user-friendly interface based on these two facilities.

See Also

• Diomidis Spinellis. The information furnace: Consolidated home control. Personal and Ubiquitous Computing, 7(1):53–69, 2003. doi:10.1007/s00779-002-0213-8
• ZoneMinder