Tuesday, October 06, 2009

Epistemic Paradox

Metro (p7) this morning has a quote from the charity Kidscape: "As criminal record bureau checks bring to light only convictions, cautions and reprimands, a sex offender who is active - but has not been found out - passes through the safety net". For this reason, they say vetting should be tightened.

Aside from the fact that an Enhanced CRB already also shows "soft evidence" (undeniable unsubstantiated rumours that weren't sufficient to attempt a prosecution, and spent convictions), this argument holds about as much water as a particularly leaky colander. It fails on fairly basic philosophical grounds - person X may be a kiddy-fiddler (ontology, "what is") but if nobody knows that (epistemology, "what is known"), they can't cause a vetting failure. That bears repeating.

If a paedophile has not been found out, no amount of vetting will block them from working with kids.

In fact, in a classic piece of security failure, the more trust is placed in vetting schemes, the more likely people are to slip through the cracks. If nobody is vetted, parents and co-workers have to rely on their judgement - judgement honed by years of experience and ├Žons of evolution - as to who to trust and to what degree; if someone is vetted, "obviously" they're safe, so there's no need to be alert. One can easily envisage a child porn ring using something like the Carnival Booth Algorithm to defeat any sort of vetting: all they need is one person who can slip through the net and they all get the resulting abuse pictures.

The new Vetting and Barring scheme is particularly stupid, as it is a one-time check with no expiry or revocation. Such things are like gold to a determined attacker: "cast iron" proof of safety based on out-of-date evidence. The more the government tightens its grip, the more people slip through its fingers.

To paraphrase something a rather wise site security officer once told me: "everyone who's ever been arrested for spying held a security clearance, it's not proof of anything".

- KoW

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