Say that you need to give your operatives a way to recognize each other. Of course you can’t give them each a full list of all your trusted spies. What if, instead, you gave them a list of secret words which are not names, but which are derived from names, as acts are derived from thoughts?

How is this useful?

Given a code name of any size, like AGONIST, and a hashing function, and some very patient mathematicians, you can produce a secret word of fixed shape, called a cartouche. Say the cartouche for AGONIST is 0AB002. See how the cartouche is six letters? You can put any word of any length into this function, you can put in LAPETIARE BEGAN THE REVOLUTION or the full text of I Summoned Antideath! but the hashing function does not care, it is set up to always yield six letters.

The names of everyone in this room—Baru and Ulyu Xe, Ake and Dziransi, Run and Ude, Nitu and Yythel—could all be given to that hashing function and made into six-letter cartouches, 038801 for Baru and 0AC802 for Ulyu Xe and so forth. And if Baru wanted to prove to Ulyu that she was on Ulyu’s list of trustworthy agents, she could say, “Run my name through the hashing function, and you will get the cartouche 038801, which is on your list. See? I am one of yours.” It would take a well-trained clerk with an abacus and some devices, but it could be done.

But the trick is that you cannot get the original name back from the cartouche, even if you know the hashing function: for many possible names might produce the same cartouche. Ulyu Xe cannot look at 038801 and say, “Oh, yes, that means Baru.” She might, if she had a lot of spare time, compute all the names that could hash into 038801—but there are too many.

Baru thought: What I see of other people is the output of a hashing function.

I’ll never know anyone’s true self, will I? Their thoughts and memories, the selfness of someone, the me-ness of me: that’s like a true name, a person in all their formless awesome grandeur. But we do not see that grandeur. We see each other only in the shapes we are forced to assume. Words constrain us, and also our laws, and our fears and hopes, and the wind, and the rain, and the dog that barks while we’re trying to speak, all these things constrain us.

We all force our true selves into little hashes and show them like passwords. A smile is a hashing function, and a word, and a cry. The cry is not the grief, the word is not the meaning, the smile is not the joy: we cannot run the hash in reverse, we cannot get from the sign to the absolute truth. Maybe the smile is false. Maybe the grief is a lie.