but "here is a thing in two parts, one of which you give to everyone but one of which you need to keep absolutely to yourself or you're screwed" doesn't have a common analogy. even the "i give you an open box with a padlock" analogy can feel a bit contrived.
However I also feel that there was no cohesive attempt at building a similar story for OpenID - which is a shame as it could be as simple as "tell us which site you want to log in via and we'll do the rest"
