Symptom Screener

Covid-19 Symptom Screener

Expanding Symptom Screening to retail, schools and restaurants using relaxed digital signatures

A team of researchers at UCLA, including researchers in the Department of Computational Medicine, have created a new cryptography-based technology for COVID-19 symptom screening that preserves privacy.  

Symptom screening is widely utilized to make workplaces safer by requiring employees to verify that they are free from any common COVID-19 symptoms, such as fever, cough, or loss of smell before entering their workplace.   UCLA’s new methodology allows for this screening to be performed anonymously, and can expand its use to other environments, such as at restaurants, stores and schools.

Individuals using UCLA’s web-based screener app provide information on their current symptoms but not any identifying information. If they are symptom-free, they obtain a certificate that they can use to gain entry to a location. The certificate contains a cryptographic digital signature developed for this application by UCLA researchers. The digital signatures guarantee the authenticity of the certificate and provide information about the time when the screener was completed.  If an individual reports symptoms, the screener app provides current public health guidelines.

The key advance in the technology is that the cryptographic algorithm allows for individuals to obtain certificates without entering any identifying information.   This greatly simplifies deployment of the system as there are no complex privacy, cyber security and legal issues involved in deploying the system.

The symptom-screening system can easily be deployed as it only requires access to smartphones to perform the screening and display certificates, and does not require the downloading of any additional software. Individuals can also access the app on the website and print out a certificate. 

Protecting Businesses, Retail and Restaurants 

The technology can be utilized to protect businesses by asking employees to take the screener each morning and show their certificate before coming to the worksite.  In addition, customers of retail establishments or restaurants can be asked to take the screener before entering as well.  The fact that the technology enables anonymous screening is what makes this possible.

Protecting Schools

One important application of the symptom screener is to help reopen schools.  Parents will use the screener to report their children’s symptoms and if they are symptom-free, the parents can obtain a certificate to present when they drop off their children at the school for the day.  Teachers and staff can use the standard screener.  In addition, the same system can be used to symptom screen visitors or any other individual coming to the school.  

Cryptographic Algorithm

The UCLA system is based on a modification of a well-known cryptographic procedure called ‘digital signature’. These digital signatures are ubiquitous and they provide evidence that a document is valid and obtained from a specific source.  In the case of the UCLA system, the signatures on the certificates provide evidence that the individual who obtained the certificate reported no COVID-19 systems when using the screener, replacing the need for collecting identifying information by traditional symptom-screening methods

However, the main limitation of existing digital signature approaches is that the signature is very long, making it impractical for symptom screening, as short signatures are required since they need to be printed and visualized on the certificate.  Traditional digital signatures can be over 100 characters long which are too long for this application.  The UCLA team developed a new scheme which we call  ‘relaxed’ digital signatures that are much shorter than traditional digital signatures, but still provide the security necessary for this application.  Relaxed digital signatures are only 16 character-long codes. 

The system is now available for public use at:


Full details of the technology are available in our preprint:

"Expanding COVID-19 symptom screening to retail, restaurants, and schools by preserving privacy using relaxed digital signatures"
Brandon Jew, Alexis Korb, Paul Lou, Jeffrey N Chiang, Ulzee An, Amit Sahai, Eran Halperin, Eleazar Eskin


Paper Abstract:

Symptom screening is a widely deployed strategy to mitigate the COVID-19 pandemic and many public health authorities are mandating its use by employers for all employees in the workplace. While symptom screening has the benefit of reducing the number of infected individuals in the workplace, it raises some inherently difficult privacy issues as a traditional approach requires the employer to collect symptom data from each employee which is essentially medical information. In this paper, we describe a system to implement Cryptographic Anonymous Symptom Screening (CASS) which allows for individuals to perform COVID symptom screening anonymously while avoiding the privacy issues of traditional approaches. In the system, individuals report their symptoms without any identifying information and are issued a completion certificate. This certificate contains a cryptographic code which certifies that the certificate was obtained from the screener after reporting no symptoms. The codes can be verified using a cryptographic algorithm which is publicly available. A standard cryptography approach to implement such a system would be to use digital signatures. Unfortunately, standard digital signatures have some limitations for this application in that the signatures are often hundreds of characters long and if the signature contains the name of the individual, then there is also a risk of compromising privacy. In our approach, we develop and utilize a relaxed digital signature scheme to provide 16 character long codes and handle names using equivalence classes which helps preserve privacy. Both of these extensions technically compromise the security but in a way that is negligible for this application. Our system can either serve the function of standard symptom screening system approaches for employees, but can also extend symptom screening to non-employees such as visitors or customers. In this case, the system can be utilized in retail, restaurants and schools to ensure that everyone in the physical space, including employees, customers, visitors and students have performed symptom screening.