[Cryptography] Crypto and rustling

[Natanael]

Den 19 nov 2016 04:28 skrev "Dave Horsfall" <dave at horsfall.org>:
>
> I've just started reading "Robbery Under Arms" (a story about
> cattle/horse/sheep rustling in Australia), and given the recent thread
> about how Enigma could be improved using only technology available at the
> time), a thought occurred to me:
>
> How would an owner design a brand that could not be altered, and how could
> a rustler get around it?  For example, the owner would not use a single
> letter (a circle for example could be branded around it), and would not
> use letters that could be altered (such as F -> E, L -> E, O -> Q, T -> I,
> etc), whereas a rustler would have to find a compliant blacksmith.
>
> In crypto terms, it should be infeasible to turn one brand into another.

Why not just use symbols which have no shared sub-patterns? Like for
example just using A, B, C, H, J, K, M, N, R, S, T, W, X, Y, Z (depending
on font, the symbol set may differ).

Every symbol should be excessively clear and stylized such that it can't be
easily transformed.

An alternative is some kind of individual logos, complex patterns where
everybody local knows all logos in use. They should likewise be designed
such that no additions (except "blacking out"  the full pattern) would
cause it to become hard to distinguish.

Now that I have I think of it, Qr codes have a similar problem. It must
tolerate any given part up to a certain size of its surface to become
completely covered, and uses error correction codes to provide the
redundancy to handle it.

What's the simplest way to design visual error correction codes that can be
processed using pen and paper? (mechanical tools are allowed)
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