In the Asian Saga series by James Clavell, the Struan family gave away the half-coins of Jin-qua: in exchange for a desperately needed loan, the pirate Dirk Struan received 4 halves of 4 coins. The Chinese merchant, Jin-qua, kept the remaining halves. The repayment of the loan came in the form of an oath: Dirk Struan and his descendants would grant a boon to whoever presented one of the four halves, with no limits and no conditions. Those who wish to become head of the Noble House, the family’s powerful trading business, must swear to uphold this promise. When fulfilling the bargain the Struan descendant gets out his original coin and checks it against the one presented to him. He keeps the coin in exchange for the favor.
How would someone make a bargain like this nowadays? The system with the original half coins could be easily broken using a modified key copier. Admittedly only four times (at most, perhaps less if they get suspicious), but for carte blanche you only need one.
- Cannot be copy-able (see below).
- Must be a physical object, though it may contain digital parts.
- Can be anything up to briefcase-sized.
- Must survive at least 5 years at room temperature and preferably 10
- Must survive rough handling to the level of an airport carry-on (but does not necessarily have to be shippable or legal to take on planes). For example, laptops meet this criteria but very thin china does not.
- Must be verifiable with a high degree of confidence. The only limit on verification procedure is that it should not take more than a week and preferably much less than that.
Let’s say the threat model is that faced by the Noble House: well-funded private companies and individuals, but not the CIA or magical assassins.