Biometrics on portable devices
Posted by aogMonday, 23 September 2013 at 14:46 TrackBack Ping URL

I was discussing the new fingerprint technology for the iPhone with SWIPIAW because she’s a computer security expert and that’s how we roll with our pillow talk.

One thing she pointed out that I had not realized is that it is in fact very hard to secure biometric information. For a password or key phrase, you get it right or you don’t. Only exact matches count. For this reason you can encrypt the actual plain text and compare only the encrypted version of the user input to that. There is no need to store the actual password so even if the device is stolen, retrieving the password is difficult.

Biometrics are quite different in that, being biological, things are never quite the same. Therefore you have to compare the key data with the input data to see if they are close enough. You can’t encrypt it because the whole point of an encryption algorithm is to scatter the input, to make sure that two inputs that are “close” end up “far away” after being encrypted.

The result here is that if you use biometrics, stealing the device easily gets you the raw biometric data, from which you can may be able to construct a facsimile for use elsewhere. Moreover, unless you want your biometric data stored everywhere, remote systems must depend on the physical device (the iPhone) to do the verification. That means physical possession is enough, the software can easily be hacked in that situation to send “it’s really him” regardless of the input or without any input at all.

On the other hand, SWIPIAW points out that many (most?) cell phone users both store sensitive data on their phones and use no security at all. Biometric may be weak, but at least it’s something so this may improve the over all security situation.

Comments — Formatting by Textile
Clovis Sunday, 29 September 2013 at 20:01

May I suggest that use of both (fingerprint and separate password) at same time looks a better idea?

Annoying Old Guy Sunday, 29 September 2013 at 23:26

Does it? What benefit does the fingerprint bring beyond the password?

Clovis Monday, 30 September 2013 at 05:45

Well, it is one more layer of security, isn’t it?

Annoying Old Guy Monday, 30 September 2013 at 07:45

Security is not additive. You don’t get more security just by layering on more of it.

Clovis Monday, 30 September 2013 at 09:41

That does not look obvious to me.

If I add one more locked door before you can reach a room, why is it not more security?

Annoying Old Guy Monday, 30 September 2013 at 13:39

Because what you’re really doing is a putting the equivalent of a realtor’s lock on the first lock, where get the key to first lock after you pick the first. The whole point of the original post is that with biometrics, you must store the key data on the device.

Clovis Monday, 30 September 2013 at 15:36

Well, AFAIK the whole point of using fingerprints is to make sure that the person is there, well, in person. Right?

So the problem here is that you do not trust to let your fingerprints everywhere, hence you want to store it in the cellphone - from where it can be stolen.

But if you ever visited buildings where they ask for your fingerprint - we have many in Brazil, given our highly insecure society - you’ll notice you do not have that option. You need to put your finger in their machine. Hence, no need to worry about storing it in your cellphone.

If, other than your fingerprints, they also ask for a password, I can only see it as “adding” another real layer of security.

Annoying Old Guy Monday, 30 September 2013 at 16:17

store it in the cellphone - from where it can be stolen.

You’re missing the point — it’s not about stealing the finger print data from the cell phone, it’s that if the cell phone is stolen, so is the finger print data so that data no longer protects the cell phone.

Clovis Monday, 30 September 2013 at 16:27

Hmm, OK, I missed your point from the begin then. I was thinking about fingerprint use in general.

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