Off-line Karma: A Decentralized Currency for Static Peer-to-peer and Grid Networks

Peer-to-peer (P2P) and grid systems allow their users to exchange information and share resources in a uniform and reliable manner. In an ideal world, users make roughly as much resources available as they use. In reality, this is not always the case, and some kind of currency or barter (called karma) is needed that can be exchanged for resources to limit abuse. Previous proposals for such systems have not taken the decentralised and non-hierarchical nature of P2P and grid systems into account. We present a completely decentralised, off-line karma implementation for P2P and grid systems, that detects double spending and other types of fraud under varying adversarial scenarios. The system is based on tracing the spending pattern of coins, and distributing the normally central role of a bank over a predetermined, but random, selection of nodes.