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As a layman when it comes to cryptography, I have recently been asking myself if there was a cryptographic equivalent of a family code of arms. I'm thinking of something asymmetric, that is future proof enough to hand down to another generation and that can be used to maybe access resources. If possible it should also have a graphical representation, similar to a QR code.

Maybe I am totally tapping in the dark, though. If that's the case, please elaborate on why this is a stupid idea.

EDIT: From suggestions, I have come to realize, that I indeed do not know what I am asking about. So here is a clarification: I want the abstract "coat of arms" to be known "publicly". The authority on that would come from documents and physical proof (signatures, pictures of it being shown by members etc.). The goal would be to make it public enough, to give people a hard time convincing someone that theirs is the real deal, when it isn't. As per suggestion from @MaartenBodewes, using a certificate seems like a great idea to reinforce that by adding a central authority. Now here is the difficult part: The abstract "coat of arms" could in my eyes be seen as an abstract lock. One that has one or a finite (reasonable) number of keys. Would it be possible to have something like that, so that one could prove beyond doubt that one had a key to that abstract lock, without exposing the key? So what I'm getting at is: There are two authenticity questions here. One is of the authenticity of the abstract lock and one is of the authenticity of the party trying to prove their membership conncted to that lock. The former can come from CA but the latter can't.

I apologize for the uneducated terminology. Also, I hope this is actually comprehensible. :)

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    $\begingroup$ Well, you could use a key pair for any of various purposes, and invent a graphical representation of public keys. But you don't get any choice in what your particular public key looks like, unless you spend a lot of work trying different ones like vanity onions. $\endgroup$
    – Squeamish Ossifrage
    Commented Apr 18, 2019 at 14:27
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    $\begingroup$ @SqueamishOssifrage: actually, if you use IBE, the public key can be anything you want. If you don't trust a central authority that can decrypt anything, then there is RSA (or Rabin or Pallier), where you can fairly efficiently preselect not quite half of the public key bits (however, it might not meet the "future proof enough" criteria...) $\endgroup$
    – poncho
    Commented Apr 18, 2019 at 14:59
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    $\begingroup$ I hardly think that a sensible self-respecting noble would trust the central authority of the monarch to handle their great family's coat of arms! After all, what happens when the anarchist peasantry rise up and behead the monarch as they are wont to do? $\endgroup$
    – Squeamish Ossifrage
    Commented Apr 18, 2019 at 15:36
  • $\begingroup$ Welcome to crypto.stackexchange - that can be used to maybe access resources - You'll need to expand upon this point more before you can receive a real answer to your question. If you define: Who/how many are the legitimate parties in an interaction, what are they trying to achieve, what is the power of the adversary, etc, then it would be much easier to answer the question. Anything can be represented by a QR code, so that part is easy. $\endgroup$
    – Ella Rose
    Commented Apr 18, 2019 at 16:58
  • $\begingroup$ Thank you for your input! I will think hard about it and edit the question accordingly. $\endgroup$
    – d.oelert
    Commented Apr 18, 2019 at 18:38

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You can put almost any information in an X.509 certificate, and then pass the private key for the matching certificate along. People can of course claim that the certificate is theirs, but when holding the private key, you can prove it belongs to you.

Of course, you might need a central authority for the certificate to be trusted, but you can send a certificate request to many CA's. Of course, if there is sufficiently weird info in there to be notified you may need to explain the applicability (and most likely, pay up, but I guess that comes with the domain). If you start to dislike the CA you can always switch to another one.

Probably easiest is to include an URL to a website with e.g. an actual coat of arms.

Digital information is usually not used to show off. If you require something more physical then you could get e.g. a gold leafed ePassport. For that you would probably need a high up person in the government (and be a complete and utter - well you can fill that one in yourself).

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  • $\begingroup$ This is great input, thank you! Also I'm pleased to have met a fellow diskworld fan. :) $\endgroup$
    – d.oelert
    Commented Apr 19, 2019 at 17:58
  • $\begingroup$ A signed PDF could act as a more literal "Coat of Arms" I suppose. An idea that came to me later. $\endgroup$
    – Maarten Bodewes ♦
    Commented Apr 19, 2019 at 18:31

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