Things may have changed since you were here. Currently, there's additional digital systems built around the e-DNI and much of the administration -national and local- uses that for most of the things where you previously just used your DNI number and a smile.

The certificates themselves in the DNI are used only occasionally, but it's mostly your decision: you can stick to using the certificates and not activate other means and then you can't access a bunch of things unless you use the certificates.

But still, this is mostly for the public administrations. Private entities, such as banks or whatever, don't really make use of it and build their own systems (most of the time quite stupid ones [0]).

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[0] Fortunately they changed it, but for about a year or so my bank decided that instead of sending a 4-digit code through SMS -which you then typed to verify whatever transaction you were doing- it was "more secure" to just show 5, 10, or 20 4-digit codes on the transaction site and then send you a single number through SMS, say "7", to select the code from the list.

And somehow this was applauded and got them some newspaper headlines as the bank investing the most in advanced security in the country or some shit like that.