Unchained Identities: Putting a Price on Sybil Nodes in Mobile Ad Hoc Networks

As mobile ad hoc networks (MANETs) and similar decentralized, self-organizing networks grow in number and popularity, they become worthwhile targets for attackers. Sybil attacks are a widespread issue for such networks and can be leveraged to increase the impact of other attacks, allowing attackers to threaten the integrity of the whole network. Authentication or identity management systems that prevent users from setting up arbitrary numbers of nodes are often missing in MANETs. As a result, attackers are able to introduce nodes with a multitude of identities into the network, thereby controlling a substantial fraction of the system and undermining its functionality and security. Additionally, MANETs are often partitioned and lack Internet access. As a result, implementing conventional measures based on central authorities is difficult. This paper fills the gap by introducing a decentralized blockchain-based identity system called Unchained. Unchained binds identities of nodes to addresses on a blockchain and economically disincentivizes the production of spurious identities by raising the costs of placing large numbers of Sybil identities in a network. Care is taken to ensure that circumventing Unchained results in costs similar or higher than following the protocol. We describe an offline verification scheme, detail the functionalities of the concept, discuss upper- and lower-bounds of security guarantees and evaluate Unchained based on case-studies.