· web telephony security

SMS Verification

I’ve received an email today from Barclaycard with the following:

“From time to time, to make sure it’s you who’s using your Barclaycard online, we’ll send you a text with a verification code for you to use on the Verified by Visa screen that’ll pop up on your payment page.”

The proprietary nature of mobile phones with the hardware specifications and the software being closed off from inspection or audit and considered to be trade secrets make my phone and my tablet the least trusted devices I own and use.

Due to this lack of trust, I’ve often held back from using my phone or tablet for certain tasks where I can still get away with not doing so. I have experimented with having read-only access to my calendars and contacts to ensure that if my phone is compromised they can’t just be wiped out, though in the end I had to give in as my calendar was becoming too difficult to manage using a paper system as part of entry for new events.

I wanted to try to reduce the attractiveness of compromising my phone. Anyone that really wants to have a go at my phone could probably get in. It’s an older Samsung Android phone on a UK network and software updates rarely come through in a timely manner. Anything that I give my phone access to is at risk and that risk needs to be balanced by some real world benefits.

These are just the problems with the phone itself. When you’re using SMS authentication, even with the most secure phone ever, you’re still going to be using the phone network. SMS authentication is about equivalent, in terms of the security it really offers, to your mobile phone number being your password when it comes to an even mildly motivated attacker. You probably don’t treat your mobile phone number as a password, nor does the provider or anyone you’ve given it to, so you can assume that it’s compromised.

Why are mobile phones so popular for two factor (on in increasing numbers of cases, single factor) authentication? Not because they improve security but because they’re convenient and everyone has one. This seems like a bad plan.


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