APRICOT - A PRIvacy preserving COntact Tracing system

Bhaskaran Raman, Shweta Mahajan, Palash Jain, Neeraj Kerkar, Shahrukh Hussain, Mayank Kush, Mohit Garg, Bhavesh Kumar, Varunesh


With pandemic like COVID-19, monitoring and controlling the spread of the crisis is a crucial part of all the countries. In the early stages, controlling such a spread can save millions of lives and help maintain a stable economy. Thus, contact tracing becomes important for the health authorities to fight the control of epidemics. There have been several efforts in building contact tracing apps in India to combat the spread of the pandemic. However, many of these solutions put user’s privacy at risk. We provide an alternative solution which can help health authorities to track and control the epidemic while preserving individual privacy. Our solution uses Bluetooth connection to communicate with the nearby devices.

1. Introduction

The COVID-19 pandemic has spread like wildfire across the globe [1]. One of the key elements in countries who have managed to control the spread of COVID-19 is the use of contact tracing [2]. In the early stages, when there are fewer cases it is easy to manually perform contact tracing. But with thousands of infected patients building contact tracing is much more difficult [3]. Countries have been employing a variety of means to enable contact tracing. Solutions that work for some countries might not work in other countries due to societal norms. Especially in India, where there is social stigma associated with the virus. There have been instances in India about the leakage of information of quarantine people and denial of services to health workers on the basis of potential risk of spread of virus through them [4]. With the absence of any data protection laws in India, collection of data and their misuse after the virus is a major threat. Further, giving the users the power to know about any infected person in close proximity can create mass panic and distrust of the system. Inspired by Singapore’s contact tracing app - TraceTogether [5], we propose a solution that preserves the privacy of the users (both infected and healthy ones) and discourages users from taking control of the system.

2. Proposed Solution

2.1 System overview

In this section we first introduce our system and then describe various models in it. Apricot includes parties such as healthy (or not yet diagnosed) and diagnosed individuals with smart phones and health authorities or medical professionals. The system can be divided in four steps such as registration, data collection, uploading contact trace and viewing contact trace.

2.1.1 Registration

The user signs up in the app using the OTP sent to the entered mobile number. The user is then assigned a 1000 pseudo-IDs. The pseudo-ID changes every 5 minutes. By using time-varying pseudo-ID, the app does keep the users private from each other.

2.1.2 Data collection

When the user is logged-in and has turned on Bluetooth, the APRICOT app announces itself to nearby APRICOT users using a pseudo-ID. The APRICOT app stores the pseudo-ID information of nearby users, along with the timestamp. This information, called the contact trace, is stored in the app. Each phone scans for the nearby devices for a time interval of 1 min. The contact history is deleted after 30 days

2.1.3 Upload contact trace

When an APRICOT user uploads (voluntarily) the contact trace from the app to the server, the APRICOT server comes to know the contact trace of that user.

2.1.4 View contact trace

The contact trace uploaded (voluntarily) by a user is to be viewed at the APRICOT server by the health authority by entering the mobile number of the person whose contact trace is to be viewed.

3. Trust and privacy model

The proposed system is designed around a model that assumes there is a semi-trusted authority maintaining the server with diagnosed carriers’ contact histories. The system is designed to minimize the amount of diagnosed carriers’ information that is exposed to other users, and to maximize the privacy for all other users of the system. However, diagnosed users do risk forfeiting some privacy when they share their contact histories with the authority managing the server. That said, the contact trace information is to be deleted at the APRICOT server after the period of disease containment.

Apricot Design

Apricot Privacy Policy


[1] “Novel Coronavirus Map from HealthMap,” March 2020. [Online]. Available: https: //www.healthmap.org/covid-19/

[2] K. T. Eames and M. J. Keeling, “Contact tracing and disease control,” Proceedings of the Royal Society of London. Series B: Biological Sciences, vol. 270, no. 1533, pp. 2565–2571, 2003.

[3] B. Chappell, “Coronavirus: Sacramento County Gives Up On Automatic 14-Day Quarantines,” https://www.npr.org/sections/health-shots/2020/03/10/813990993/coronavirus-sacramento-countygives-up-on-automatic-14-day-quarantines, 2020, accessed: 2020-03-23.

[4] Subhashis B, Bhaskaran R, Subodh S, “Apps for Covid: to do or not to do”, Ideas for India, 2020

[5] “Help speed up contact tracing with TraceTogether,” Singapore Government Blog, March 2020. [Online]. Available: https://www.gov.sg/article/help-speed-up-contact-tracing-with-tracetogether