Proplets -- Devices for Controlling Property
Copyright (c) 2001 by Nick Szabo
redistribution without permission of the author prohibited
Civilization has highly evolved practices for determining whether certain
actions are allowable or not, or who should prevail in a dispute,
namely law. Such a body of knowledge cannot be reinvented
from scratch, so instead e-commerce security should draw heavily on it --
building property rights, contract and tort law into technology
at a very basic level. Proplets define the basic security
for local evidence gathering, enforcement, and negotiation of such
Proplets do not rely on central planning, AI,
or a single trusted third party for any function.
Central planning is not able to account for
the distributed and diverse knowledge and preferences of different people.
third party" is a nice-sounding synonym for a wide-open
that a designer chooses to overlook. Proplet design places strong emphasis
on eliminating such exposures.
The key is building in, at the most basic level of technology,
code (in both the legal and software sense) that allows a widely
distributed people, each person having his own unique information,
preferences, to cooperate within well known, mutually agreeable, and
strongly enforced constraints. With these constraints the risks
and benefits of technology are balanced, weapons are monitored
and securely restricted in their use to only very narrow, specific, lawful
for every person there is more profit from peace than from destruction.
The goal of proplet design is to control physical objects with digital
protocols. Proplets protect its structure and function from
non-owners, and observe the environment for phenomena impinging
on a region, on matter, or on its owner. A proplet is an
electromechanical device (e.g. a MEMS device)
with the following core abilities:
A proplet may optionally also have the following abilities:
- It knows who owns it
- It knows where it is in space and time
- It can communicate securely with nearby proplets, over
a public network, and with its owner
- It contains a computer, called the ownership module, that is a
secure extension of the owner's trusted computing base
- The ownership module securely exercises control over a machine
via entanglement (explained below), or over nearby inanimate matter
via sensors, effectors, public registration, and law.
- It can securely recognize nearby proplets owned by the same owner
- It can cooperate with nearby proplets, especially those owned by the
same owner or under contract with the owner. This can include
the manufacture of larger structures and machinery.
- Guest computation modules -- extensions of the trusted computing
base of a non-owner of the proplet for purposes of rapid protocol
communications. The guest can store proprietary data and programs
on the proplet in his guest modules where they are inaccessible to
the owner, except through services designed by the guest. The guest
modules also can locally execute smart contracts with the owner.
- Deed modules -- these operate the smart contracts, or deeds,
created by previous owners to bind future owners.
No computational module can be read or controlled by physical
tampering -- it will shut down, erase itself, or even self-destruct
depending on the severity of tampering. Computational modules
are "transparent" to their
publically registered controller and opaque to other entities.
Only protocols that are simple and composable with provable security
govern the communications between the security kernel (private key
operations), control box, sandbox, and other components of a computation
modules. Similarly for communications between modules and between
How does a proplet find out who owns it, or a guest module who
controls it? There are two basic ways:
A proplet's guest modules are publicly listed and transferred
independently of each other and of the proplet's ownership module.
- It looks up the public key of its current owner or guest in a public
and follows instructions signed with the
corresponding private key, or
- It follows instructions signed by the private key held by home
proplets. Home proplets live on or inside the owner or guest.
Transfer of remote proplets (or guest modules) occur with the
transfer of the home proplets that govern the remotes.
With the home proplet alternative, biometric control of the home
proplets may replace public ownership records.
Proplets control electronics directly from ownership or guest
modules. Proplets control machinery via entanglement.
Entanglement can take at least two forms:
Entanglment designs have in common that they make it too expensive
for the attacker to steal the electronics or machinery by severing
it from the controlling proplet.
- Firing sequences, without which the machinery cannot work.
(Digitally timed high performance automobile engines and nuclear
explosives are two contemporary examples).
- Direct nanomechanical linkages.
Deeds, in the context of replicated property titles and proplets,
are smart contracts executed by a deed module. The current owner
may add new deeds agreed to (but not remove old ones) by drafting signing
and signing such a smart contract with other current property owners.
The deed binds both properties (perhaps to different terms, depending
on what the two current owners have negotiatied). The
deed modules can be audited at any time by the contemporary owners
of other proplets bound to the deeds.
Founders of competing property title registries define master
deeds, or tort laws, to govern disputes within registry properties. They
also define tort law for disputes between their properties
and properties defined by other registires, by coming to agreements
with those registry founders. Founders also create the initial
Founders are often the manufacturers of proplets. They
build in a particular registry as authoratative for their proplets
as well as designing an accompanying tort law.
For example, the founder of registry of fixtures in a
spatial region can sign an agreement with a movable
property (chattel) registry, governing the behavior of chattel moving
through space and interacting with fixtures. The manufacturers
of chattel and fixtures program their proplets to respect the
appropriate registries and constrain their sensors and effectors
to follow the tort law that has been agreed to.
Proplets combine our most highly evolved practices for cooperation
on a large scale with a technology architecture suitable for advances
well into the future, even well into posthuman civilization. Proplets
provide a much sounder footing for solving the problems of high
technology cooperation including problems such as privacy, weapons
of mass destruction, and other abuses of the power of advanced
Computer Security as the Future of Law,
Formalizing and Securing Relationships on Public Networks, Nick Szabo
Secure Property Titles, Nick Szabo
My thanks to Gregory Burch, J.D. for his helpful questions.
Please send your comments to