Barclays and the single factor authentication

In my previous post on the topic I have barely touched on one of the important reasons why I did not like Barclays at all. The reason for that was that I still had money into my account with them, and I wanted to make sure that was taken care of before lamenting further on the state of their security. As I managed to close my account now, I should go on and discuss this further, even though I have touched upon the major topics of this.

Barclays online banking system relies heavily on what I would define as “single factor authentication”.

Usually, you define authentication factors as things you have or things you know. In the case of Barclays, the only thing they effectively rely upon is “access to the debit card”. Okay, technically you could say that by itself it’s a two-factor system, as it requires access to the debit card and to its PIN. And since the EMV-CAP protocol they use for this factor executes directly on the chipcard, it is not susceptible to the usual PIN-stripping attacks as most card fraud with chip-and-pin cards uses.

But this does not count for much when the PIN of the card they issued me was 7766 — and to lament of that is why I waited to close the account and give them back the card. It seems like there’s a pattern of banks issuing “easy to remember” 4-digit PINs: XYYX, XXYY, etc. One of my previous (again, cancelled) cards had a PIN terribly easy to remember for a computerist, at least not for the average person though: 0016.

Side note: I have read someone suggesting to badly scribbled a wrong PIN on the back of a card as a theft prevention. Though I like that idea, I’m just afraid the banks won’t like it anyway. Also it would take some work to make the scribble being easily misunderstood for different digits so that they can try the three times needed to block it.

You access Barclays online banking account through the use of the Identify method provided by CAP, which means you put the card into the reader, provide the PIN, and you get an 8-digits identifier that can be used to login on the website. Since I’m no expert of how CAP works internally, I will only venture a guess that this is similar to a counter-based OTP, as the card has no access to a real-time clock, and there is no challenge provided for this information.

This account access sounds secure, but it’s really not any more secure than an username and password, at least when it comes to dealing with phishing. You may think that producing a façade that shows the full Barclays login, and proxies the responses in real time is a lot of work, but the phishing tools are known for being flexible, and they don’t really need to reproduce the whole website, just the parts they care about getting data from. The rest can easily be proxied as it is without any further change, of course.

So what can we do once you can fool someone into logging in to the bank? Well, you can’t really do much, as most of the actions require further CAP confirmation: wires, new standing orders, and so on so forth. You can, though, get a lot of information about the victim, including enough proofs of address or identity that you can really mess with their life. It also makes it possible to cancel things like standing orders to pay for rent, which would be quite messy to deal with for most people — although most of the phishing is not done for the purpose of messing with people, and more to get their money.

As I said, for sending money you need to have access to the CAP codes. That includes having access not only to the device itself, but also the card and the PIN. To execute those transactions, Barclays will ask you to sign a transaction by providing the CAP device with the account number and the amount to wire. This is good and it’s pretty hard to tamper with, hopefully (I do not make any guarantee on the implementation of CAP), so even if you’re acting through a proxy-phishing site, your wires are probably safe.

I say probably, because the way the challenge-response is implemented, only the 8-digits account number is used during the signature. If the phishers are attacking a victim that they studied for long enough, which may be the case when attacking businesses, you could know which account they pay every month manually, and set up an account with the same number at a different bank (different sort code). The signature would be valid for both.

To be fair to Barclays, implementing the CAP fully, the way they did here, is actually more secure than what Ulster Bank (and I assume the rest of RBS Group) does, with an opaque “challenge” token. While this may encode more information, the fact that it’s opaque means there is no way for the user to know whether what they are signing is indeed what they meant to.

Now, these mitigations are actually good. They require continuous access to the card on request, and that makes it very hard for phishing to just keep using the site in the background after the user logged in. But they still rely on effectively a single factor. If someone gets a hold of the card and the PIN (and we know at least some people will write the real one on the back of the card), then it’s game over: it’s like the locks on my flat’s door: two independent locks… except they use the same key. Sure, it’s a waste of time to pick both, so it increases the chances a neighbour would walk in on wannabe burglars trying to open the apartment door. But there’s a single key, I can’t just use two separate keychains to make sure a thief would only grab one of the two, and if anyone gets it from me, well, it’s game over.

Of course Barclays knows that this is not enough, so they include a risk engine. If something in the transactions don’t comply with their profile of your activity, it’s considered risky and they require an additional verification. This verification happens to be in form of text messages. I will not suggest that the problem with these is with GSM-layer attacks, as that is still not (yet) in the hands of the type of criminals aiming at personal bank accounts, but there is at the very least the risk that a thieve would get a handle of my bag with both my card and my phone, so the only “factors” that are still in my head, rather than tied to the physical objects, are the (provided) PIN of the card, and the PIN of the phone.

This profile fitting is actually the main reason why I got frustrated with Barclays: since I had just opened the account, most of the transactions were all “exceptional”, and that is extremely annoying. This was compounded by the fact that my phone provider didn’t even let me receive SMS from the office, due to lack of coverage (now fixed), and the fact that at least for wires, the Barclays UI does not warn you to check your phone!

There is also the problem with the way Barclays handle these “exceptional transactions”: debit card transactions are out-and-out rejected. The Verified by Visa screen tells you to check your phone, but the phone will only ask you if it was your transaction or not, and after you confirm it is, it’ll ask you to “retry in a couple of minutes” — retrying too quickly will lead to the transactions being blocked by the processor directly, with a temporary card lock. The wire transfer one will unblock the execution of the wire, which is good, but it can also push the wire to after the cut-off time for non-“Faster Payments” wires.

Update (2017-12-30): since I did not make this very clear, I have added a note about this at the bottom of my new post, about the fact hat confirming these transactions only need you to spoof the sender, since the content and destination of the text message to send are known (it only has to say “Y”, and it’s always to the same service number). So this validation should not really count as a second factor authentication for a skilled attacker.

These are all the reasons for which I abandoned Barclays as fast as I could. Some of those are actually decent mitigation strategies, but the fact that they do not really increase security, while increasing inconvenience, makes me doubt the validity of their concerns and threat models.

2 thoughts on “Barclays and the single factor authentication

  1. It also makes it possible to cancel things like standing orders to pay for rent, which would be quite messy to deal with for most people — although most of the phishing is not done for the purpose of messing with people, and more to get their money.

    Is this meant as an extension on the preceding thought (mess with their lives) or as something you can do from the bank GUI? I’ve never seen a UK banking website in my life, mind you, but at my current main bank you have to confirm any such modification just the same as any old payment or wire transfer.

    Like

  2. You can do that through the Online Banking at Barclays without further confirmation.Barclays *will* notify you, by text message, of a standing order being cancelled — the next day. No paperwork will be pushed for this and it’s an easy to miss notification particularly when they send you *three* messages for each other transaction that needs to be confirmed.

    Like

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

w

Connecting to %s