Credit-based Reputations for Identity Management with Blockchain and Flow Networks

Whitepaper proposal for the 04/2017 ‘Rebooting Web of Trust’ Design Workshop

    11 April 2017
    Tobias Mayer, Omar Hasan, Lionel Brunie
    Institut National des Sciences Appliquées (INSA) de Lyon, Laboratoire LIRIS
    { tobias.mayer // omar.hasan // lionel.brunie} @insa-lyon.fr

ABSTRACT

A secure management of digital identities is an obvious requirement for digital technologies and applications (digital payment, online shops, insurances, etc.). It is typically achieved by pre-defined certificate-based trust. However, pre-defined trust on centralized instances is not always possible or wanted for trust management and the “web-of-trust” emerged as a decentralized alternative. It determines a trust value by aggregating reputations issued by other entities, where the reputations represent a subjective evaluation of the user satisfaction. This mechanism is also suitable for the identity management when using reputations to indicate (the subjective impression of) an identity’s trustworthiness. However, such traditional reputation-based web-of-trust approaches suffer from Sybil attacks, where an identity can increase the own trust value by creating synthetic identities issuing reputations.

We propose a trust management mechanism for the decentralized reputation-based web-of-trust approach, which operates among two avenues. First, issuing reputations imposes spending some credits, which are received through reputations and the total amount being limited in the system. In order to prevent Sybil attacks, circular reputations are not allowed, which is determined by applying flow network concepts to verify reputation validity. Second, identities and reputations are stored in a blockchain where and identity’s trust value can be determined by traversing the stored blocks and aggregating related values accordingly. The proposed mechanism is fully decentralized, able to prevent threats such as Sybil attacks or reputation flooding, offers secure and immutable storage characteristics, where any action can be cryptographically verified.

CONTEXT

Identity management with a web-of-trust (WoT) cannot rely on pre-defined trust as provided by certificate authorities in public key infra¬structures (PKI). To this end, WoT aggregates reputation values in a distributed manner. However, we cannot draw conclusions among off- and on-line identities such that any trust value is fully determined by activities and reputation values provided on-line. Malicious nodes can exploit this aspect, e.g. by creating additional identities to increase the own trust values through synthetic reputations. Moreover, reputation integrity and accountability need to be ensured. The blockchain theory has recently revolutionized the concept of electronic cash by eliminating the requirement of trusted third parties and by providing true decentralization. Its secure immutable distributed data storage is therefore crucial for reliable reputation-based trust management.

We consider therefore the problems (1) that the pure aggregation of reputations is not sufficient and we require mechanisms to prevent reputation misuse or colluding parties; and (2) that a blockchain model shall be able to support and maintain trust & reputation information.

PROPOSED APPROACH

We propose a new identity management approach based on reputation and flow networks. Reputations are provided by spending some credits where the total amount of credits is limited in the system. This prevents misuse such as Sybil attacks through the imposed value and credit limitations. The economic mechanics serve thus as trust generator in addition to the absence of centralized pre-defined trust.

We consider a system, where identities are represented by self-contained data (public key, unique id, etc.) and are able to provide reputations to other identities. A reputation is considered as a positive feedback for the receiving identity. The amount of received reputations represent the amount of available credits to spend and reputations can be provided as long as the issuing identity has sufficient credits. However, we require that circular reputations are not possible to prevent misuse (i.e. identity B cannot provide a reputation to identity A if B has received on by A beforehand).

We leverage flow networks to determined circular dependencies and total credits available per identity as illustrated in Figure 1. Blockchain will be used to store provided reputations. Trust management aspects are integrated into the blockchain architectural design and the consensus algorithm (see section implementation possibilities).

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Figure 1: The reputation (R) of each identity is determined by the amount of incoming reputation values that serve as credits (C) for issuing reputations. Here with a limit of 100 credits in the system and I2 being the first node in the system and thus initially owning some credits.

OPEN QUESTIONS

IMPLEMENTATION WITH THE DATACOPP PLATFORM

“DataCOPP” is an incubating project developed by T. Mayer at the INSA de Lyon with the aim to develop a high-performance hybrid blockchain as distributed platform for privacy-preserving data processing. The underlying blockchain architecture differs from those used in the ID-BLOCKCHAIN project (context of the proposed identity management approach). However, some of its design concepts can be beneficial for the realization of credit-based reputation approach and an architectural integration as outlined in the following:

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Figure 2: DataCOPP asset management operations for the entities of a traceability layer.

ACKNOWLEDGEMENT

The introduced approach has been developed in the context of the ID-BLOCKCHAIN project with Paymium and Ledger as industrial partners (https://idboussac.github.io).