Skip to main content

Reverse authentication for banking

A persistent problem with retail banks is that they phone you and then ask you for information.  A common scenario is that the bank's fraud department calls because of a suspicious debit or credit card transaction.  What follows is, from a security perspective, dangerous.

Either the bank just assumes that you'll accept that they really are your bank (and not some random person trying to get private information from you) or they'll go through some weak authentication (such as telling me half my postcode).  Sometimes they have the audacity to call me and then ask me to prove that I am me even though they just called me.

All this ridiculous nonsense can be fixed by use of the two factor authentication tokens that banks are now giving out.  In the UK Barclays has PINSentry, HSBC has Secure Key, NatWest has Card-Reader.  These tokens are usually used for logging in to online banking or authorizing a transaction, i.e. they are used so that you can prove to your bank that you are you.

But they can be used the other way around.

Imagine the phone ringing in your home:

Caller: Hello, Mr Foo it's Barclays Fraud Department calling.  We need to ask you about a transaction on your account?

You: OK

Caller: Do you have your PINSentry handy? I'd like to use it to prove that this is Barclays calling.

You: Yes, I have it right here.

Caller: Please switch it on.  A six digit number will appear on the screen.  I'm going to tell you the first three digits.

You: OK, it's on.

Caller: The first three digits are 4 7 2.  You should be able to see it on the screen.  That proves that this really is Barclays calling as only we would be able to predict the next three digits.

You: Yes, I see that.

Caller: And can you tell me the other three digits?  That way I'll know you really are Mr. Foo.

You: Yes, it reads 4 9 7.

Caller: Great.  Let's talk about the transaction our system has flagged...

With a simple conversation like that you've proved that you are you, and the bank has proved that they are who they say they are. Additional levels of authentication can be added (such as asking for personal information), but the key is that the two factor device contains a secret shared between your bank and you.


Anonymous said…
When the bank does this to me I:
a) tell them is bad security and they are training people to be phished. The length of this discussion depends on what kind of mood I am in.

b) Tell them I will ring them back to discuss the issue.
whoppie said…
This happened to me three times and the third time I asked to talk to the manager, then I told him to google the word phishing. Then I switched bank to another one and so far they haven't been stupid enough to do the same thing...
whoppie said…
This happened to me three times and the third time I asked to talk to the manager, then I told him to google the word phishing. Then I switched bank to another one and so far they haven't been stupid enough to do the same thing...
If the bank gives you three digits and the customer gives back three, you can then call 500 customers or so, successfully guess the digits for one of them, scam the other three out and log in to their account. I think this isn't quite the right protocol.

Popular posts from this blog

Your last name contains invalid characters

My last name is "Graham-Cumming". But here's a typical form response when I enter it:

Does the web site have any idea how rude it is to claim that my last name contains invalid characters? Clearly not. What they actually meant is: our web site will not accept that hyphen in your last name. But do they say that? No, of course not. They decide to shove in my face the claim that there's something wrong with my name.

There's nothing wrong with my name, just as there's nothing wrong with someone whose first name is Jean-Marie, or someone whose last name is O'Reilly.

What is wrong is that way this is being handled. If the system can't cope with non-letters and spaces it needs to say that. How about the following error message:

Our system is unable to process last names that contain non-letters, please replace them with spaces.

Don't blame me for having a last name that your system doesn't like, whose fault is that? Saying "Your last name …

All the symmetrical watch faces (and code to generate them)

If you ever look at pictures of clocks and watches in advertising they are set to roughly 10:10 which is meant to be the most attractive (smiling!) position for the hands. They are actually set to 10:09.14 if the hands are truly symmetrical. CC BY 2.0image by Shinji
I wanted to know what all the possible symmetrical watch faces are and so I wrote some code using Processing. Here's the output (there's one watch face missing, 00:00 or 12:00, because it's very boring):

The key to writing this is to figure out the relationship between the hour and minute hands when the watch face is symmetrical. In an hour the minute hand moves through 360° and the hour hand moves through 30° (12 hours are shown on the watch face and 360/12 = 30).
The core loop inside the program is this:   for (int h = 0; h <= 12; h++) {
    float m = (360-30*float(h))*2/13;
    int s = round(60*(m-floor(m)));
    int col = h%6;
    int row = floor(h/6);
    draw_clock((r+f)*(2*col+1), (r+f)*(row*2+1), r, h, floor(m…

Importing an existing SSL key/certificate pair into a Java keystore

I'm writing this blog post in case anyone else has to Google that. In Java 6 keytool has been improved so that it now becomes possible to import an existing key and certificate (say one you generated outside of the Java world) into a keystore.

You need: Java 6 and openssl.

1. Suppose you have a certificate and key in PEM format. The key is named host.key and the certificate host.crt.

2. The first step is to convert them into a single PKCS12 file using the command: openssl pkcs12 -export -in host.crt -inkey host.key > host.p12. You will be asked for various passwords (the password to access the key (if set) and then the password for the PKCS12 file being created).

3. Then import the PKCS12 file into a keystore using the command: keytool -importkeystore -srckeystore host.p12 -destkeystore host.jks -srcstoretype pkcs12. You now have a keystore named host.jks containing the certificate/key you need.

For the sake of completeness here's the output of a full session I performe…