REPUTATION IN ETHEREUM
TRUSTDAVIS
Ethereum Meetup
6/18/2014

Overview
• Online Trust and Reputation in General
• Parts of a Reputation System
• Types of Reputation Systems w/ Applications
• TrustDavis as Transaction Insurance
• TrustDavis on ethereum
• Variants & References
• Q & A

Cryptocurrency is…
• A digital currency made possible by
cryptography (duh)…
• A digital payment system…
• A decentralized application running on a
block chain…
• A community with a very loose set of
common interests, goals and desired
behavior (various)

Community Goals?
• We want our crypto assets gain in value and
adoption
• We want to be able to freely and privately
transact
• We seek to maximize gain through
disintermediation (p2p ftw)
• We seek to minimize loss & risk of default
• We avoid trusting central authorities or
other single points of failure

Trust & Reputation
• Trust: Firm belief in the reliability, truth, ability, or
strength of someone or something. "relations have
to be built on trust“
– Synonyms: confidence, belief, faith, certainty, assurance, conviction, credence
• Law: Confidence placed in a person by making that
person the nominal owner of property to be held or
used for the benefit of one or more others
• Archaic: To allow credit to (a customer)
• Layman: Do what you say you’ll do when you say
you’ll do it.

Trust & Reputation
• Reputation: The beliefs or opinions that are
generally held about someone or something.
"his reputation was tarnished by allegations that he
had taken bribes"
– Synonyms: name, good name, character, repute,
standing, stature, status, position, renown, esteem,
prestige.
• In the absence of firsthand knowledge, we
rely on reputation to establish initial trust.

The Need for Trust
• It is often said that cryptocurrency technology
(bitcoin, ethereum etc.) replaces the need for
human trust via self-enforcing smart contracts.
• This is simply not the case. In fact we are trading
trust in one set of entities for another. We are
changing and flattening our “trust stack”.
Centralized Decentralized
Self Self
Trading Partners Math/Code/Developers
Trusted Intermediaries Network/Miners
Legal Systems Trading Partners
Government DAO/DAC (optional)

Shrinking the Community
• Taking gov’t and civil institutions out of the mix
brings us back to smaller, village like communities
• Dunbar number is approx. 150
• You’ll run into approx. 10,000 during your lifetime
• Online is pseudonymous with very low identity
creation cost
• In the cryptocurrency world, traditional legal
recourse is difficult. Code is law (Lessig)
• Everything on the chain is open and transparent

Parts of a Reputation System
(Farmer & Glass, 2010)
• A source makes a claim about a target
• Explicit (claim) vs. Implicit (behavior)
• Global (e.g. FICO) vs. Local (e.g. Yahoo Chess rating)
• Reputation is context specific
• Claim types: Qualitative, Quantitative, Raw,
Normalized, Ranked, Scalar
• Roll-Ups: Counters, accumulators, averages, mixes
and ratios
• Routers: Messages, Decisions and Termination

A slightly-more-evolved model.
Now, articles are ranked not only
according to endorsements, but
also the amount of discussion
they generate (Farmer & Glass).

Reputation Models w/ Applications
(Farmer & Glass, 2010)
• Content:
– Favorites & Flags (vote to promote)
• Reddit, Digg, StackExchange, various for a
– Karma (participation, quality, robust)
– This or That voting (was this review helpful?)
• Yelp, Yahoo
• Transactions: Ratings, Reviews & Points
– eBay
• Achievements & Badges
– Public recognition, Gamification

TrustDavis (DeFigueiredo & Barr)
1. Agents can accurately estimate risk
– Third parties provide accurate ratings
– Parties are liable for the references they provide
2. Honest buyer/seller avoids risk (if possible)
– Insure transactions
– Buyers/sellers pay for references to insure their transactions
3. No advantage in obtaining multiple identities
– Agents can cope with pseudonym change
– References are issued only to trusted identities
4. No need to trust a centralized authority
– No centralized service needed
– Anyone can issue a reference

(DeFigueiredo & Barr)

Key Ideas (DeFigueiredo & Barr)
• Incentive Compatibility
– Incentive to accurately rate
– Incentive to insure
– No incentive to change pseudonym
• Saving gains in excess of the opportunity cost to
insure future transactions.
• Insurers can profit by charging premiums for
references. They must estimate risk accurately.
• Buyers/Sellers be insured against
loss/default/non-performance

TrustDavis on ethereum
• Ethereum makes this easier
• We don’t need v2 or any other reinsurance
agent because they cannot default (they
escrow up front). This simplifies things.
• We use a factory contract (project Douglas
style “form” contract) which has been
audited using Mintchalk’s new binary search
feature.

A TrustDavis ethereum contract
• First Run:
– Register the contract
– Store the buyer and seller address
– Store the amount for the transaction and the expiry
date
• Subsequent Runs:
– Check expiry (blocks or Chronos)
– Look for presence of “completed transaction” votes
by buyer AND seller
– Look for presence of “failed transaction” votes by
buyer OR seller
– Store escrowed references from insurers
• (amount, vs. buyer or seller, premium)

A TrustDavis ethereum contract (2)
• If Expired:
– Refund the premiums?
– Return the escrow to insurers
– Return the escrowed buyer’s funds
• If Failed:
– Transferred claimed amounts to both parties
– Transfer premiums to insurers
– Transfer agreed funds from buyer to seller
– Register failure on Reputation Registry (sendmsg)
• If Succeeds:
– Transfer premiums to insurers
– Transfer agreed funds from buyer to seller
– Register success on Reputation Registry (sendmsg)

Variants using ethereum
• No False Claim: Either party can declare the transaction
defaulted. In this case all insurers must pay. Similar to no
fault insurance.
• False Claim with Arbitration: Arbiter(s) are jointly chosen
and do not hold escrowed funds. Claim is settled based on
ruling.
• Revocable References: Insurers can withdraw references
prior to the transaction moving forward. This may occur due
to new knowledge gained or new opportunities.
• Invested Escrow: References and other contract balance
deposited into an interest bearing account until transaction
completion. Withdrawn and redistributed upon completion.
• Writing to a Reputation Registry: Upon completion of the
transaction, references and disposition are written to a
reputation registry. This registry could accumulate a credit
score implemented as an uncirculated subcurrency.

Conclusion (DeFigueiredo & Barr)
• We can now have an automated, simplified
version of TrustDavis on the block chain
– Accurate Ratings
– Non-Exploitable strategy for honest agents
– Pseudonym change tolerance
– Decentralized Infrastructure
• We are bootstrapping from a “dead money”
escrow model to a reputation model

References/Further Reading
• DeFigueiredo & Barr. TrustDavis: A Non-Exploitable Online
Reputation System (2005).
http://www.cs.ucdavis.edu/~defigued/index_files/trustdavis.
pdf
• Farmer & Glass, Building Web Reputation Systems, O’Reilly
Press (2010). http://buildingreputation.com/doku.php
• Fukuyama, Trust: The Social Virtues and The Creation of
Prosperity (1996).
• Kamvar, Schlosser & Garcia-Molina. The EigenTrust
Algorithm for Reputation Management in P2P Networks.
Proceedings of the 12th International WWW Conference
(2003). http://en.wikipedia.org/wiki/EigenTrust

QUESTIONS?