Although I don't remember having a strong contact, the contact confirms that APP has come to "notify"

Novel coronavirus contacted to confirm APP "COCOA" released in June, and the author also used it from the date of release, and received a notice that "may be exposed to COVID-19" a few days ago.

However, even if notified, the contact cannot be confirmed on the application. It seems that this is almost a failure of the phenomenon, the author does not necessarily have a strong contact with the infected. After searching the Internet, it was found that the same phenomenon was reported as Chirahora. This doesn't seem to happen very often, but because it's rare, I'd like to report what happened.

First of all, as a prerequisite, outline the outline and structure of COCOA.

COCOA is an application program developed and used by the Ministry of Health and Labor of Japan. When you do not know, the infected people and people with strong contact should be notified of contact, promote the correspondence of early examination and isolation, and prevent the spread of infection. This is an application that Apple and Google jointly developed and embedded in iOS and Android using the "Exposure Notification" mechanism, which can be used on iPhone and Android phones.

Smartphones with COCOA are automatically exchanged with nearby smartphones via Bluetooth as the "key" of inherent information. The keys received will be kept in the smartphone for 14 days. The Ministry of Health and Labor publishes a new key list of people who confirm infection every day, and COCOA checks whether the saved key is consistent with the key sent. If there is a key match, it is "contact with the person confirmed to be infected in the past" and is notified.

COCOA users who confirm infection in medical institutions can submit their own keys sent in the past 14 days to the Ministry of Health and Labor at will. The Ministry of Health and Labor summarizes its key points and publishes it to COCOA users across the country every day. Of course, even if people who do not use COCOA are confirmed to be infected, the key will not be sent, so even if contacted, it will not be notified.

Roughly speaking, although the above structure, but actually to protect privacy by distinguishing the use of several keys, or a combination of encryption and hashing, doing a variety of things. This is a structure that does not deal with any location and personal information and cannot be "tracked" even if it can be "notified".

For those who want to know more, please read the specifications published by the Ministry of Health, Apple and Google.