5 April, 2004: Is all hope now lost?

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More ID cards idiocy. Now we are apparently to get a compulsory card scheme by 2008; this is apparently inspired by warnings from the security services: (reported in a story in the Independent and elsewhere)

Ministers were told that in several recent arrests, police found people with papers giving them multiple identities, and the politicians stressed the importance of making sure the ID cards could not be forged.

Two points:

  1. The cards will be forgeable -- it simply isn't possible to make an unforgeable card.
  2. If everyone is to have a card then they'll have to get them by using existing identity documents. People who already have identity documents for multiple identities will be able to get multiple identity cards.

The proponents of the scheme counter the second of these with the fiction that biometric information can be used to ensure that only one card is issued to each person. This won't work, because the false positive rates for identification by biometrics are too large.

Suppose that the comparison of (say) iris photographs is 99.99% accurate: that is, when you compare my iris photograph against my reference photograph, the system identifies me correctly in 9,999 out of 10,000 cases, and says it's not me one time in 10,000. Similarly, when you compare my iris photograph against someone else's, 9,999 times out of 10,000, it says it's not me, and one time out of 10,000 it says it is me.

Now suppose that I go down to ID Cards 'R' Us (proprietor: Capita plc., most likely) to get an ID card. My iris is photographed, and to ensure that I'm not a Bad Evil Terrorist, my iris photograph is compared against the reference photographs for everyone else in the database (about 40,000,000 people). Even with a 0.01% error rate, the system will come up with 4,000 matches to me -- that's 4,000 people who have to be individually checked to make sure that they're not actually false identities that belong to me.

(Note that in real systems the false accept rate is likely to be different from the false reject rate; it's the false accept rate we care about here.)

Now, according to this report on an iris recognition system tested by the US Department of Defence, the false accept error rate for a typical current system is claimed to be one in a million by its manufacturer, but in practice is probably more like one in 90,000. That gets us down to about 444 people who have to be checked as potential false matches for each ID card issued. If we believe the manufacturer, then it's 40. If you believe that we can afford to investigate in detail the backgrounds of 40 people for each new ID card issued -- which is what will be necessary to ensure that you issue exactly one ID card to each person in the population -- then you're more of an optimist than me. (Optimistically, we can cut out half those matches as being of the wrong gender, and maybe another half as being too different in age to be the same person. But that's still ten people who need to be checked. Doing this properly would be insanely expensive.)

Of course, in reality what will happen is that Crapita (or whatever other contractor puts in the cheapest bid for the system) will hand the sodding things out to all and sundry with no proper checks at all. Sir John Stevens, Commissioner of the Metropolitan Police, yesterday said on TV that,

I think the sooner [ID cards are] brought in the better and as a professional police officer I have to tell you we need them.

If his attitude is typical of the Police (other evidence suggests that many officers are better informed) we're in real trouble, since the result will be that the authorities trust that the ID card system will have its advertised effect -- of making it impossible to adopt a false identity -- while in fact leaving it as easy to create false identities as it ever was, and to have them legitimised by a shiny piece of plastic too.

My sober assessment? We're doomed. All we can hope for is that the terrorists are more incompetent than our government seems to be.

New rule: every time I write a long rant about ID cards, I'll also post another holiday photo for those readers who find ID cards boring (that's probably all six of you, I fear). However, this one is a bit bleak:

Ruined windmill, with barbed wire

Copyright (c) 2004 Chris Lightfoot; available under a Creative Commons License.