Knowledge Based Questions

Quickie today, as I have somewhere else to be!

In the Spiderman animated series, there was a story arc where Peter finally manages to marry his high-school crush, Mary Jane. It all seems good until he finds out that the woman he married is actually a clone of the real MJ, who had died previously. Ever since then, I occasionally have these crazy flights of imagination where I wonder if the people I know have been replaced by clones.

In Harry Potter and the Deathly Hallows, Harry is moved to a safe location by the Order of the Phoenix, and part of the journey involves having other members of the order take a polyjuice potion so that they look like Harry. When they reach their destination, they ask each other a series of knowledge-based questions in order to verify that they are who they say they are, and not an enemy impersonating them with a polyjuice potion of their own. Things like, "What's the first thing I asked you when we were at X?"

The big problem with those kinds of questions, if you haven't agreed to them beforehand, is that they're susceptible to forgetfulness. I cannot remember the first thing I said to most people. There are some people I don't even remember meeting!

Something that MrFodder and I encountered not long ago. We were joking around, but ended up setting up a secret question that we both knew the answer to, and that nobody else would know the answer to. I think we did it maybe 6 or 7 years ago. Something I tend to do when someone around me behaves in an unusual way is I ask if they're an impostor (as a joke). We were out at lunch, and MrFodder was saying some things that were completely out-of-character. So I said my usual line, but this time, I asked him whether he remembered our secret question.

He could not.

However, this is not unusual for him! It took him many years to remember my birthday, and he often forgets other things that to me seem to be crucial information. So what was I to do?

On one hand, he couldn't establish his identity by answering our secret question. On the other hand, forgetfulness is part of his personality, so by not remembering our secret question, he was, in a way, verifying his identity.

It's a tricky question, and things like this plague the information security industry, because there has to be a balance between security and usability.

For my sake, given that we're getting to our 10-year anniversary, I really hope I haven't married a Hydro Man clone...