We have been using the term „certificates“ for a long time for files that are used to encrypt or sign data or to prove identity.

Now „certificates“ have become something that we use in our daily life to show that we are vaccinated or tested against Covid-19.

Because they are provided as QR-codes and people are used to thinking of QR-codes as a way to encode an URL in a machine readable way, many people think that this means that the certificates are actually stored on a server and just retrieved from there. Which again causes a lot of resistance against the certificates and the requirement to have them and to show them. They suggest using the „yellow book“ instead, which has worked just fine for providing proof of vaccinations.

But things have changed. Today a lot depends on being vaccinated and some people are really scared of the vaccinations, for example some internet stars spread the rumor that people will die a few years after the vaccination. How do they know less than that number of years after the first person has been vaccinated? I guess it is their secret. But today there are millions of people who are really willing to pay good money for a falsified yellow vaccination book and it is not really that hard to do that. So in the end of the day, the yellow book cannot be trusted any more.

Now, what is it with the certificate?

Just think of a text file that contains the relevant information. JSON, XML or something like that.

  • Who?
  • valid until?
  • what (test/vaccination/…)?
  • count of vaccinations (1/1, 2/2, 3/3…)
  • type of vaccine (mRNA…)?
  • Product (Moderna/BionTech/SputnikV/…)?
  • Producer?
  • Country (last) of vaccination?
  • Date of (last) vaccination?
  • Serial number of shot

More or less something like this…

Now this file is digitally signed by a universally trusted entity, like the ministry of health. So the person who performs the vaccination creates this file, transmits it to the ministry of health, where it is cryptographically signed and then it is transmitted back as a binary file, whose integrity can be verified by the signature, using the public key of the ministry, but it cannot be changed or created without the private key of the ministry, which needs to be kept safe in the ministry. A lot of really important things rely on this public key cryptography, so it should be OK for this purpose as well.

Now this binary file is just encoded as QR-code. Not the URL of the file, the actual contents. When we show the certificate and the person checking it is serious about it, they use an app that can read the QR-code and decode it to show the contents of the original text file in a nice format and ensure that it is exactly what has been signed by the ministry.

Now the ministry promises that it does not store a „backup“ of the certificate that it signed, once it is done. So the data is deleted shortly after having been signed. We can believe this or not. If we assume that they store data about our vaccinations and tests etc., then yes, they do that. But they do not need the certificate for that. They can get the information anyway without creating a certificate for us.

So I guess it is a pragmatic approach to use these certificates as a relatively fraud safe method to prove that one has been vaccinated or tested or gone through a Covid-infection. The yellow books should not be accepted any more and actually they are less and less. And of course the certificate with the QR-code on the phone or on a piece of paper is only better than the yellow book, if they really verify it with an app and if they check some ID as well.

This technology has a lot of interesting applications that we might make use of in the time after Covid-19.

Tickets for Railroad, Flight, Theater, Cinema, Museum,… can be personalized and done in a way that is hard to forge. We actually see this already today. Now there could be a digitalized passport on the phone as well, which is signed by the issuing authority. For many purposes that could work as well as the paper passport. Now think that this passport and the ticket can be matched, i.E. one trusted person checks that the passport and the ticket and the person travelling match and from than on the combined certificate containing the passport and the ticket can be shown, which would make things easier and more efficient and more relyable than having to show ticket and passport again and again.

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