I learn something

The Schnorr token method. I thought it would work like this.  A schnorr group is the set of remainders among the multiplicative integers when they all have the prime integer designated in secret.  So, each member will be a member of the set of remainders, and can be verified from the prime number that i a factor in them all.

Wiki:  Implementations of protocols that use Schnorr groups must verify where appropriate that integers supplied by other parties are in fact members of the Schnorr group;

And the techno folks working on the sandbox kow about this and it seems to be a prime candidate.  Different token services can set up their own groups of 'remainders' and have them installed in your smart card. Tis means the card can generate tokens that verify aiuthorized trading.  But each app mut now the  verification service appropriate to the token s generated in that prime group.

Nor will this be the only key method, but, they work because the hardwarew vendors generating the flAt chips can have the keys inserted, robotically, and unobserved by humans.  A general set of keys for retail hopping and invewting.  But, keys can be installed, with a person visit.

Redundancy and separation

Specifying a particular key to generate tokens does not oblige you to use a particular ledger service. That can be specified in one of the other fields in the sandbox interface.  Most retailers just accept the standard tokens, the ones generated by factory installed keys. Person to person (looking at each other) transactions have little to hide between the parties, tokens not even needed often since honest accounting is hardware protected.

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