## Enabling Contextual Proof

So far, we have covered methods to establish the what (with a
cryptographic digest), the who (a digital signature), the when (trusted
timestamp) — now we need to establish the where, or the context of a step
relative to the others.

We do this by establishing contextual (and cumulative) proof using a hash
chain.

First, we create another digest for the entire step (the digest,
signature, and timestamp, so far), which we can call a link hash.

Then we insert that link hash into the following step of the process along
with the digests of the other key factual elements.

By including the proof of its previous step, every step in effect contains
the proof of all its previous steps, forming a cumulative proof. Thus, we
have a chain of cumulative proofs to ensure the contextual proof.

By sharing a cumulative proof of a specific step, we share the proof of
all its previous steps as well. Alice can just carry the digest of the
final step — which is effectively proof of all the steps of her Battleship
game.

Cumulative proofs are tamper-proof — to change the result of one, you
would have to go all the way back to the first step to change the proofs
in all previous steps, which would in turn invalidate the entire process.

In this way, we are able to demonstrate the where of a step.

As the proof of an entire process can be represented by the digest of the
final step, we could include the proof of one process inside a step in
another proof of process graph. The link hash of the final step of the
outer process graph would thus demonstrate both proofs of its steps, as
well as proof of the steps of the inner process graph.

In this way, we can seamlessly connect multiple processes. For example,
the proof of Alice’s Battleship victory could be connected to the proof of
her victory in a Backgammon game to establish a reputation profile in a
network of board game enthusiasts who wish to assert their refined taste
in an era of rapid-fire, deliberately addicting console and mobile games.

In this paper we have used examples of individual sources of trust for
timestamping. However, the factual element of when (and thus, where) can
also be established through consensus on a common timeline.

A common timeline can be established through a blockchain network in which
participants agree to contribute computational power through a clearly
defined consensus logic for the acceptance of new blocks (process steps)
of information that define the when and where of a proof of process graph.

Read more about blockchain consensus logic mechanisms: bitcoin whitepaper,
proof of work, proof of stake.