Sybil-Resilient Coin Minting

Abstract: We describe a distributed coin minting protocol that mints one coin per time unit for each member in a digital community. The protocol assumes that community members use a trust-graph to determine the genuineness of digital identities, and that doing so bounds the number of sybils (fake or duplicate identities) in the community, but does not completely eliminate them. The main goal of the protocol is to be resilient to the sybils that penetrate the community, in the sense that, in the long run, only genuine identities mint coins. The protocol accepts that sybils penetrate the community from time to time (by gaining enough trust within the trust-graph), yet assumes that every sybil is eventually exposed. Since coins minted by a sybil will most probably circulate by the time it is exposed, the protocol puts the responsibility for introducing a sybil onto its trusting neighbours and confiscates subsequent coins minted by them, until the coins minted by that sybil are accounted for. In particular, the protocol confiscates two coins for each coin minted by the sybil: one to recover what was wrongly minted and one as a fine for introducing the sybil in the first place. We argue that this approach constitutes a mechanism to deter the introduction of sybils into the community and to incentivize sybil hunting (using part of the confiscated money as a reward).