An ill-conceived California bill endorses a blockchain-based system that would turn COVID-19 test results into permanent records that could be used to grant access to public places.

EFF and ACLU oppose California A.B. 2004. The newest version of this bill would create a pilot program for using “verifiable health credentials” to report COVID-19 and other medical test results. The bill defines such a credential as “a portable electronic patient record,” for which authenticity “can be independently verified cryptographically.” The bill’s fact sheet explains that these credentials “use blockchain technology” to create “a provable health record” for purpose of “travel, returning to employment, immunization status, and so on.” Three rounds of official bill analysis provide the same explanation.

This bill is a blockchain solution in search of a problem, and COVID-19 is a problem that will not be so easily solved.

That’s a huge privacy concern. No one should have to unlock their phone and expose their health information in order to gain entry to their office, school, or neighborhood market.

Medical test results are a poor fit for public ledgers. First, per the recommendations of California’s Blockchain Working Group, the “most critical question” when considering adopting blockchain technology is whether “a permanent record [is] warranted.” Here, it clearly is not. A person’s COVID-19 status may change from day to day, and tests are often hard to come by. This system could unfairly punish those who can’t afford to be tested nearly constantly. Second, while verifiable credentials might make sense for reporting a binary fact (such as whether or not a person is 21), medical tests come with strong caveats and significant margins of error. For example, some COVID-19 diagnostic tests have a false negative rate as high as 20 or 30%. The science behind testing for COVID-19 immunity is even less settled. According to the CDC, “we do not know how much protection [COVID-19] antibodies may provide or how long this protection may last.” This nuance is lost when a test result is turned into a credential. In short, this bill is a blockchain solution in search of a problem, and COVID-19 is a problem that will not be so easily solved.

Worse, the bill would take us a troubling step towards a national identification system. It would habituate people to present a digital token as a condition of entry to physical spaces, and habituate gatekeepers to demand such digital tokens. Such systems could be expanded to track every occasion that a person presented their digital token, or to prove other pieces of personal information like age, pregnancy, or HIV status. Further, such systems would create new information security problems when people hand their unlocked phones to gatekeepers, and create new social equity problems given the one-in-five people who don’t have a smartphone.

EFF and ACLU also opposed an earlier version of this bill. You can read here our lengthier explanation of this bill’s many problems. We urge the California legislature to reject A.B. 2004. It will do nothing to address the COVID-19 crisis, and much to invade our digital rights.