Note: this is a post saying how this is possible, not indicating that you should do so. And it's not permanent, it will just make them hate you until it's fixed.
So I noticed about a year or so ago that a friend of mine, who plays World of Warcraft, uses a token device, called "The Blizzard Authenticator", more information can be found here
It generates a 6 digit numeric code that has to be inputted along with the username and password of the user. One simple way to effectively DoS the user is to simply steal the keychain, whereas a smarter way, which will probably make them think that something's wrong with the token, and probably spend lots of time trying to fix it, is simply by pressing the button around 10 times or so.
Since tokens generate a (pseudo-)random number, it means that hitting the button enough times will make the device show every code in the whole keyspace of 000000-999999. And because of this, technically every number is a valid number, but if it just took every 6 digit number as correct, it would give no added security. The way they get around this is have a Window of Acceptance. They take the last 6-digit code used in the user's last successful login, and do the random function on it (the same one used by the token device to bring out the next code), this should give the next code, however this also means there is only a window of acceptance of one code, which is pretty ridiculous as it means if you accidentally press the button twice, you've wasted all your money on a token. So they have a window of acceptance that's larger, perhaps 5 or 10. So they do this function on each subsequent result, and have a list of codes that can be accepted.
World of Warcraft isn't the only application of tokens, the reason I used WoW for this blog post is partly because I know somebody that uses one of the devices, and partly because of what one has to do to fix it. On the WoW wiki, it shows that if your token breaks, you need to contact the World of Warcraft billing department with the following information:
- Your full real name.
- Your full address including postal or zip code.
- Your full email address (currently registered on the account).
- Your account name.
- The authentication key used to create the account.
- Your Secret question and answer.
- The last 4 digits of the credit card used on the account plus the expiration date OR the full code of a game card activated on the account.
- A legible fax, scan or photo of a piece of government-issued photo identification, such as a passport or driving license matching the first and last name of the registered account owner. (No idea if this is kept on record but I sure hope not)
- A legible fax, scan or photo of the Authenticator token, with the code on the back fully visible.
This is an immense amount of security for a game (perhaps even too much). I'm really impressed as there are banks with less security than this (probably because sending photos of ID and the broken token would take so long)
So in the end, if you know somebody who plays WoW, and they use a token device, don't go around pressing the token device 10 or 20 times (or giving them to small children who will just do the same). Or if you do, expect them to be annoyed until they manage to get it reset, which judging by how much information they need to give, may take a while.
p.s. I don't play World of Warcraft, I'm not a fan, but I think Blizzard are doing a decent job to make people feel protected against others stealing their account, and in the end, I feel tokens are a good idea.