added a first take on claimant model

There might be a few inconsistencies and errors.  To be discussed!

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+# Claimant model
+## **System<sup>CHECKSUM</sup>**:
+System<sup>CHECKSUM</sup> is about the claims made by a _data publisher_.
+* **Claim<sup>CHECKSUM</sup>**:
+	_I, data publisher, claim that the data_:
+	1. has cryptographic hash X
+	2. can be located using X as an identifier
+	3. has properties Y (_"ecosystem specific_")
+* **Statement<sup>CHECKSUM</sup>**: signed checksum<br>
+* **Claimant<sup>CHECKSUM</sup>**: data publisher<br>
+	The data publisher is a party that wants to publish some data to an
+	end-user.
+* **Believer<sup>CHECKSUM</sup>**: end-user<br>
+	Belief is based on seeing a valid Statement<sup>CHECKSUM</sup>.
+* **Verifier<sup>CHECKSUM</sup>**: any interested party<br>
+	These parties try to verify the above claims.  For example:
+	* the data publisher itself (_"has my identity been compromised?"_)
+	* third-parties that want to look further into the data (_"ecosystem
+	specific_")
+* **Arbiter<sup>CHECKSUM</sup>**:<br>
+    There's no official body.  Invalidated claims would affect reputation.
+
+**Example.**
+The published data could be an executable binary from a reproducible build.  The
+ecosystem-specific claim would be that the corresponding source code can be
+looked-up in a public database using X as an identifier.  A rebuilder would
+verify this claim by compiling the source, comparing the hashed output to the
+claimed value.
+
+## **System<sup>CHECKSUM-LOG<sup>**:
+System<sup>CHECKSUM-LOG</sup> is about the claims made by a _log operator_.
+It adds _discoverability_ into System<sup>CHECKSUM</sup>.  Discoverability means
+that Verifier<sup>CHECKSUM</sup> can see all Statement<sup>CHECKSUM</sup> that
+Believer<sup>CHECKSUM</sup> will accept.
+
+* **Claim<sup>CHECKSUM-LOG</sup>**:
+	_I, log operator, make available:_
+	1. a globally consistent append-only log of Statement<sup>CHECKSUM</sup>
+* **Statement<sup>CHECKSUM-LOG</sup>**: signed tree head
+* **Claimant<sup>CHECKSUM-LOG</sup>**: log operator<br>
+   Possible operators might be:
+	* a small subset of data publishers
+	* members of relevant consortia
+* **Believer<sup>CHECKSUM-LOG</sup>**:
+		Believer<sup>CHECKSUM</sup> and
+		Verifier<sup>CHECKSUM</sup><br>
+	Belief is based on two factors:
+	1. seeing a valid Statement<sup>CHECKSUM-LOG</sup>
+	2. seeing a number of valid Statement<sup>CHECKSUM-WITNESS</sup> from
+	independent instances on System<sup>CHECKSUM-WITNESS</sup>
+	
+	A _policy_ defines the exact conditions that must be met.
+* **Verifier<sup>CHECKSUM-LOG</sup>**: System<sup>CHECKSUM-WITNESS</sup><br>
+	Witnesses verify the log's append-only property from their own local
+	vantage point(s).
+* **Arbiter<sup>CHECKSUM-LOG</sup>**:<br>
+	There is no official body.  The ecosystem at large should stop using an
+	instance of System<sup>CHECKSUM-LOG</sup> if cryptographic proofs of log
+	misbehavior are preseneted by some Verifier<sup>CHECKSUM-LOG</sup>.
+
+## **System<sup>CHECKSUM-WITNESS<sup>**:
+System<sup>CHECKSUM-WITNESS</sup> is about making the claims of a log operator
+_trustworthy_.
+* **Claim<sup>CHECKSUM-WITNESS</sup>**:
+	_I, witness, claim that_:
+	1. System<sup>CHECKSUM-LOG</sup> provides a locally consistent append-only
+	log
+* **Statement<sup>CHECKSUM-WITNESS</sup>**: signed tree head
+* **Claimant<sup>CHECKSUM-WITNESS</sup>**: third party<br>
+	Examples of parties that may take on this role include:
+	* members of relevant consortia
+	* non-profits and other reputable organizations
+	* security enthusiasts and researchers
+	* log operators (cross-ecosystem)
+	* monitors (cross-ecosystem)
+	* a small subset of data publishers (cross-ecosystem)
+* **Believer<sup>CHECKSUM-WITNESS</sup>**:
+		Believer<sup>CHECKSUM</sup> and
+		Verifier<sup>CHECKSUM</sup><br>
+	Belief is based on seeing a valid Statement<sup>CHECKSUM-WITNESS</sup>.
+* **Verifier<sup>CHECKSUM-WITNESS</sup>**: n/a <br>
+	Witnesses are trusted parties.  Security is based on _strength in numbers_.
+* **Arbiter<sup>CHECKSUM-WITNESS</sup>**:<br>
+	There is no official body.  Invalidated claims would affect reputation.