libcontrac ReadMe

libcontrac is an implementation of the Apple/Google Contact Tracing API.

See the draft specs: https://www.apple.com/covid19/contacttracing/

Install

If you have autoconf you can install like this:

autoreconf --install
./configure
make
make install

You can also run the unit tests and build the documentation:

make check
make doxygen

Usage

Include header files.

#include "contrac/contrac.h"
#include "contrac/rpi.h"
#include "contrac/dtk.h"
#include "contrac/rpi_list.h"
#include "contrac/rpi_list.h"
#include "contrac/matches.h"

Broadcasting and uploading keys

Most of the functionality is managed through the opaque Contrac structure.

Create and initialise the structure as follows. The update call updates the Daily Tracing Key and Rolling Proximity Identifier based on the current time.

Contrac * contrac = contrac_new();
// Generates a random Tracing Key if one hasn't yet been set
contrac_update_current_time(data);

Get the Rolling Proximity Identifier for broadcast in Bluetooth beacons.

// Returns a buffer containing RPI_SIZE bytes of data
unsigned char const * rpi = contrac_get_proximity_id(contrac);

Get the Daily Tracing Key to upload to a Diagnosis Server in case of a positive test result.

// Returns a buffer containing DTK_SIZE bytes of data
unsigned char const * dtk = contrac_get_daily_key(contrac);

Receiving and matching keys

Add RPIs captured via Bluetooth to an RPI list.

RpiList * rpis = rpi_list_new();
// Add bytes captured at a given time to the list
rpi_list_add_beacon(rpis, captured_bytes, time_interval_number);

Construct a list of DTKs using data downloaded from a Diagnosis Server.

DtkList * dtks = dtk_list_new();
// Add data downloaded from a Diagnosis Server to the list
dtk_list_add_diagnosis(dtks, dtk_bytes, day_number);

Having collected these two lists any matches can be tested for as follows.

MatchList * matches = match_list_new();
match_list_find_matches(matches, rpis, dtks);

if (match_list_count(matches) > 0) {
	printf("Exposure identified, follow medical advice\n");
}

Cleaning up

Finally, clean up.

match_list_delete(matches);
rpi_list_delete(rpis);
dtk_list_delete(dtks);
contrac_delete(contrac);

Licence

libcontrac is released under the GPL v2 Licence. Read COPYING for information on the license.

Contact and Links

Library home page: https://www.flypig.co.uk/contrac

API documentation: https://www.flypig.co.uk/docs/libcontrac/

Source code from git:

git clone git@www.flypig.org.uk:libcontrac

I can be contacted via one of the following.

My website: https://www.flypig.co.uk
Email: at david@flypig.co.uk

llewelld/libcontrac