In this paper, we discuss the question how physical
statements can be proven remotely over digital communication
channels, but without using classical secret keys, and without
assuming tamper-resistant and trusted measurement hardware in the location of the prover. Examples for the considered physical statements are: (i) \"the temperature of a certain object is X
°C\", (ii) \"two certain objects are positioned at distance X\", or (iii) \"a certain object has been irreversibly altered or destroyed\". In lack of an established name, we would like to call the corresponding security protocols \"virtual proofs of reality\" (VPs).
While a host of variants seems conceivable, this paper focuses
on VPs in which the verifier has handed over one or more
specific physical objects O_i to the prover at some point prior
to the VP. These \"witness objects\" assist the prover during the
proof, but shall not contain classical digital keys nor be assumed
tamper-resistant in the classical sense. The prover is allowed to
open, inspect and alter these objects in our adversarial model,
only being limited by current technology, while he shall still
be unable to prove false claims to the verifier.
In order to illustrate our concept, we give example
protocols built on temperature sensitive integrated circuits, disordered optical scattering media, and quantum systems. These
protocols prove the temperature, destruction/modification, or
relative position of witness objects in the prover\'s location. Full
experimental realizations of these schemes are beyond the scope
of this paper. But the protocols utilize established technologies
from the areas of physical unclonable functions and quantum
cryptography, and hence appear plausible also without such
proof. Finally, we also discuss potential advancements of our
method in theory, for example \"public virtual proofs\" that
function without exchanging witness objects Oi between the
verifier and the prover.
Our work touches upon and partly extends several established cryptographic and security concepts, including physical unclonable functions, quantum cryptography, and interactive proof systems.