Schneier on Security: Fun with Secret Questions

Entertaining (though I've already read this one...).

I have a more interesting game I play with bank security questions that's more useful, though -- and applies to the most common usage (where the bank provides the question to you).

Simply this -- for each question, imagine how easily you could guess the answer even knowing nothing about the account owner. I'm not talking about real analysis here, just roughly mapping out the answer space.

For example, "In what city/town did ___?" is a common question. Well, if it's a US bank, probably you're dealing with US cities, and there are fewer than 20K. (Already, whoa: a three character alphanumeric password has 10 times the possibilities). Then of course cities should be weighted by population, so since NYC is biggest... well, New York has 8.3 million of the USA's 311.6 million population, the answer to this question will be New York City about 2.6% of the time.

"What's the first name of your [specified grandparent]?" is another good one. How diverse are first names, generally, particularly a few generations back? Of course there's a long tail, but otherwise... not that diverse, and it's trivial to find stats on most common names in the early 1900s. I've never chosen this question even before I started thinking hard about security, because it was blazingly obviously a bad question -- the banks would ask for my maternal grandfather's name, and I was named after him.

Fun, no?

I almost always pick something like "What's your favorite color?" and answer with random noise (say "a3tcuh487wchaowiudh23doch3298ahraui"). The rationale is that if I forget my password, I'll likely forget the secret question as well. I only want the secret question to be as hard, or harder, to guess than my password.

I wonder though, if the human at the other end will accept "just a bunch of letters and numbers" as a correct answer.

Original date of this article: April 30, 2010. Too bad it wasn't April 1st.

Q: What is your mother's maiden name?

A: I never use my mother's REAL maiden name in a security question; that is much too easy to look up with Google.

When I'm allowed to pick the question, I invariably pick "Which is it?", and the answer is a series of random words.

Now you know, identity thieves.

My bank has a particularly horrible one:

"What sports team do you most like to see lose?"

Especially considering it's a regional bank in the northeast US, you can probably hit well over 90% of accounts using less than a dozen answers.

Why the hell is anyone answering "What was your mother's grandfather's maiden/first name" or "What city were you born in" with real answers, or even real names/cities??

While entertaining, choosing the question "What is the air speed velocity of a laden swallow?" is not particularly good security.

While I have a hard time imagining Bruce just lifted someone else's blog post without crediting (more likely it was passed on to him in conversation?), this post predates Schneier's by over a year: http://tcoverride.blogspot.com/2011/05/security-questions.ht....

Thats brilliant. A big opportunity to introduce call centre agents to Monty Python quotes!

Q: Ennyn Durin aran Moria. Pedo mellon a minno.

A: Mellon!