A clockwork Analytical engine / Enigma machine, that does something equivalent to public key verification (though I assume you don’t want that kind of machine either).
In each city is a temple of the Sigils, in which are stored the Sigils of people, in public view. The Sigils are like intricate signatures drawn on clay tablets; but they are made on a special clay, Sigil Clay, that dries in about a minute, and changes color depending on the pressure you apply to it, the heat (depending of whether you’re touching it with a stylus or with your fingers), and how dry it is. Sigil Priests know hundreds of drawing techniques, and when an alternate pair is created, each person will be taught a few techniques to apply to his drawing, with no overlap between the alternates (so it should be quite hard for someone to reproduce his alternate’s Sigil). Being able to draw one’s Sigil is generally considered a proof of identity, and since only the Sigil Priests know how to make Sigil Clay, one has little opportunity to practice drawing someone else’s Sigil (not to mention that it’s of course considered a grave crime).
For the prisonner’s case, why not having the “day” persona return to prison to sleep and give a new passphrase short (randomly generated with a special set of dice) to the guard, and when he wakes up and wants to get out, he must give the same passphrase (if he gets it wrong, he is lightly punished and must wait at least 30 minutes before trying again.
The passphrase idea you describe is probably fine for minimum and even medium security, it’s just vulnerable to eavesdropping and message-passing by third parties if the prisoner has friends.
A few possibilities:
A clockwork Analytical engine / Enigma machine, that does something equivalent to public key verification (though I assume you don’t want that kind of machine either).
In each city is a temple of the Sigils, in which are stored the Sigils of people, in public view. The Sigils are like intricate signatures drawn on clay tablets; but they are made on a special clay, Sigil Clay, that dries in about a minute, and changes color depending on the pressure you apply to it, the heat (depending of whether you’re touching it with a stylus or with your fingers), and how dry it is. Sigil Priests know hundreds of drawing techniques, and when an alternate pair is created, each person will be taught a few techniques to apply to his drawing, with no overlap between the alternates (so it should be quite hard for someone to reproduce his alternate’s Sigil). Being able to draw one’s Sigil is generally considered a proof of identity, and since only the Sigil Priests know how to make Sigil Clay, one has little opportunity to practice drawing someone else’s Sigil (not to mention that it’s of course considered a grave crime).
For the prisonner’s case, why not having the “day” persona return to prison to sleep and give a new passphrase short (randomly generated with a special set of dice) to the guard, and when he wakes up and wants to get out, he must give the same passphrase (if he gets it wrong, he is lightly punished and must wait at least 30 minutes before trying again.
This is a weird and interesting premise!
The passphrase idea you describe is probably fine for minimum and even medium security, it’s just vulnerable to eavesdropping and message-passing by third parties if the prisoner has friends.