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Digital IDs (and/or "ID cards") suddenly very topical again! @AldesLibDems have been working on a briefing for our parliamentarians for a while, so I've been thinking about it a lot! There are some risks:
1. Creation of a "papers, please" society where ID is required more often, makes ethereal transactions less common and excludes those without access to particular ID from ever greater swathes of public life.
2. Oversharing of credentials is a risk, and from what we see of #privacy controls today, quite likely. Retailer might need to verify age, but oh, looks like they also verified if I have a driving license! (You *know* Halfords would do that!)
3. ID schemes that use a common identifier across different services make it much easier to do data fusion and linkage, compounding problems of de-anonymisation and privacy risks from data mining.
4. ID schemes that use active requests to the ID provider give that provider a lot of insight into how and where you're using your ID. Is it any of their business?!
5. ID systems necessarily taxonomise and impose categories upon people. Does your gender assertion make life even harder for trans people? Does it reflect the variability of human identity as it exists informally? Do non-binary identities exist in your system?
Most of those problems can be solved through design and engineering. Although a lot of ID systems *don't* solve them. We must be clear about the risks and introduce measures to mitigate them.
Fundamentally, though, ID systems are technology of control. They regularise and limit social activity. Well designed, they mightn't have an appreciable negative impact...
But very, very frequently technologies of control do not recognise edge cases, engineer out any nuance or discretion, and leave those on the periphery of society dealing with the inconvenience, cost and damage.
I'm not at all confident that the engineering professions, policy makers or politicians that'll be involved in any potential ID scheme know how to avoid those problems. 
/ends
/ends
