Sounds like you're referring to a one-time pad[1], which is what that grid looks like. Google's 2-factor auth has a simpler version of this -- they just give y

Sounds like you're referring to a one-time pad[1], which is what that grid looks like. Google's 2-factor auth has a simpler version of this -- they just give you 10 or so one-time passwords. I like the grid; it seems to have a much longer potential "lifetime" of use. [1]: http://en.wikipedia.org/wiki/One-time_pad http://en.wikipedia.org/wiki/One-time_pad