Ways in which data give you away - redaction, and phone keyclicks

1. Redacting information - careful with your spreadsheets and Word documents etc

Earlier today I read the rather interesting story of the unwittingly-released personal data of residents in a London borough, via the MySociety newsletter.

A Freedom of Information request was made to find out who had been provided council housing and the council obliged with information in an Excel spreadsheet. Although sensitive data was not overtly available it was available in 'hidden sheets' which are recoverable by fairly minor geek skills. MySociety links to a page on Microsoft's site that shows how to do this.

While few people downloaded these files (I don't know who downloaded them or what they did with that info) this information should have been redacted.

Redaction involves properly removing something, not just hiding it. A failure to redact or bungled attempts can be unfortunate and amusing and in some cases can draw attention to the fact that an attempt has been made to hide something ;)

Whenever you email a Word document to someone, unless you've removed some of the details the recipient can see when you began editing it, how long you've spent editing it, and the document's author (may or may not be you). Generally this is no big deal and I can't actually think of a time when I've bothered to / needed to do this (the version of Word I have actually prompts you for this, inviting you to make a version more suitable for sharing).

You can also read the much more hyperbolic version of the story from the local paper.

Other posts in the Word tips series...

Redaction and FOI
Paul Bradshaw of Help Me Investigate posted on his blog that any claims made by organisations that redaction will eat into their costs are likely to be nonsense. Apparently there's been a ruling on it: "we find that a public authority cannot include the time cost of redaction when estimating its costs."

2. Mobile phone keyclicks - it's possible to work out what number you're dialling
On the bus this morning someone dialled a number on their mobile and as they had keyclicks on every number entered made that little 'number being entered' sound. This particular person was using the classic two-tone sounds that dial phones make (you can hear each of the tones here, in the DTMF* number keypad bit) - each number has two separate tones combined to form a chord.

*Dual-tone multifrequency signalling

I wondered how easy it would be for someone listening to be able to instantly know which numbers were being entered. Even if someone couldn't do it live a recording of the keyclicks (admittedly it's fairly unlikely that anyone would bother to do this!) could be played back and the number uncovered. While I don't have perfect pitch and could only guess the intervals between the dialled 'notes' I'm sure there are people who could hear the number being dialled live. I've listened to all the tones and I think that some of the numbers 'sound' warmer than some of the others (chords are less dissonant I suppose) but that's about it - I can differentiate them but can't remember which is which.

After I tweeted this idea, @minifig (Thom) replied to suggest that if a recording was made then playing it down the handset of an old style phone would probably be sufficient to ring that number too. After much childhood playing with telephones I know that pressing the button (that indicates when the handset is replaced) several times at different rates could get the phone to do different things so this seems pretty likely - this was later confirmed by tweets from @schrodingerskit and @drjohnmitchell

@JoBrodie @minifig that is correct and is the basis of old-school phone phreaking en.wikipedia.org/wiki/Phreaking
— Schrodinger's Kitten (@schrodingerskit) July 26, 2012

@jobrodie You also used to get phreaks that could get free call by vocalising a tone.
— John Mitchell (@drjohnmitchell) July 26, 2012

Thom also linked to this video of a 2 year old child who can recognise numbers just by hearing them dialled - I suppose it it can't be that rare to be able to do this but I wonder how many people / toddlers have really noticed that the numbers sound different.

 

Funnily enough when I was young my dad gave me a musical calculator which played a unique note (not the dual-tone)  for each number. Although a bit like something out of Close Encounters of the Third Kind I can still remember the 7-note melody that my childhood home phone number made.

Geeky asides aside, this sounds like useful ammunition in trying to get people to switch off the annoying keyclicks on their phone.  I might have to learn the number sounds to be more convincing about this ;)