There is a lot of talk about it in these hours but how does the famous "green certificate" really work? What is hidden behind that little box that is indecipherable to sight? The Green Pass will be made mandatory in Italy from August 6 as a “passepartout” to be able to do practically anything, including going to concerts and restaurants . On seeing it well, it appears to us as a strange symbol, made up of many small black and white squares arranged in an apparently random manner. In reality, the Green Pass is nothing more than a QR code, a technology increasingly used especially in the era of Covid.
The vaccination certificate
The Green Pass has now become the true undisputed protagonist – together with vaccines – of this second (and hopefully last) time in the fight against the Covid-19 pandemic. Made mandatory for many activities already in many European countries such as France, Spain, Greece and Denmark, Italy has also decided to follow the same line. From 6 August, in fact, to access museums, gyms, swimming pools, amusement parks but also cinemas, theaters, bars and restaurants it will be mandatory (for all those over 12 years old) to show the QR code to certify possession of the Green Pass , even in the white area.
How can I get the Green Pass?
The Green Pass can be obtained in three different ways, and takes on a different validity depending on the case. It is issued to those who have carried out a swab with negative results, to those who have recovered from Covid, or to those who have received at least one dose of the vaccine. In the first case the vaccination certificate has a duration of 48 hours, in the second 6 months from the date of healing, while in the third case the validity is 9 months . Those who fall into at least one of these three categories can download their QR code certifying possession of the Green Pass from the website www.dgc.gov.it , or directly through the Io and Immuni apps .
Green Pass and QR code, how does it work?
Just like we do when we browse a digital menu in a pizzeria, or to open the train ticket, also to verify the possession of the Green Pass it will be necessary to frame the QR code. In this case, however, just any reader will not be enough. Only VerificationC19 , the official app released by the Ministry of Health is able to open the code . In fact, by framing the QR code with any app, no results will appear (try to believe it!). VerificationC19 is the Italian version of “EU Digital COVID Certificate Verifier APP”, the European app that verifies the authenticity of the Green Pass starting from the QR code. It is a completely open source application, whose source code is available on Github ( android , iOS ).
What's written in the Green Pass?
The content of the QR code of the Green Pass (whose specifications have been released in a European Union document ) is nothing more than a string of characters appropriately encoded Base45 and compressed with zlib . It contains a number of useful information, including the type of dose administered (first or second) and the type of vaccine, for who did it. Otherwise, it certifies the negative outcome and the date of the tampon or the date of healing from Covid-19. Not only that, perhaps the most important data is the so-called digital signature, which ensures the authenticity of the Green Pass and that only the official app can decode . Finally, there are also the name, surname and date of birth.
The QR code: a barcode but faster
But what is the QR code? QR stands for "Quick Response", which is a "quick response" code . Born in 1994 in Japan, the QR code has established itself in recent years as the evolution of the traditional bar code. In reality it is much more because it was designed to be used in a simpler and more intuitive way. With the camera of a smartphone or tablet it is possible to frame the QR code and trace all the information "hidden" inside.
How do we write all this information in such complicated code?
The QR code is a two-dimensional matrix composed of many small black and white squares, arranged in such a way as to encode a fairly large amount of information. In the standard format, the code is capable of encoding more than 7000 numeric characters and more than 4000 alphanumeric characters, for a maximum size of about 3 kilobytes . When the smartphone frames the QR code, an application (in most cases already available in the phone's camera) decodes the message by associating 0 to the white squares and 1 to the black ones. Very often it is a URL that refers to a website where other information is contained, given the small capacity of the QR code.
QR code, but which one?
In 1997 the Japanese company Denso Wave (which invented the QR code) made the use of this technology with a free license, standardizing it for the first time. Many do not know, however, that six other QR code standards have been released, including the one currently in use since 2015 . Not only that, in addition to the Standard QR code, there is also the Micro QR code. Released in November 2004, it can represent smaller content (up to 35 digits and 21 alphanumeric characters).
An almost infallible technology
The QR code also implements a four-level (L, M, Q and H) error correction technique using the Reed-Solomon Code . With this non-binary error detection and correction algorithm, the QR code is able to guarantee the readability of even partially damaged symbols, restoring up to 30% of their content (level H) . We understand well, therefore, how the QR code is becoming increasingly used also in official and institutional contexts, as in the case of the Green Pass.