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The Sybil attack in computer security is an attack wherein a reputation system is subverted by forging identities in peer-to-peer networks. Detweiler on the Cypherpunks mailing list and used in the literature on peer-to-peer systems for the same class of attacks prior tobut this term did not gain as much influence as "Sybil attack".
In a Sybil attack, the attacker subverts the reputation system of a peer-to-peer network by creating a large number of pseudonymous identities, using them to gain a disproportionately large influence. A reputation system's vulnerability to a Sybil attack depends on how cheaply identities can be generated, the degree to which the reputation system accepts inputs from entities that do not have a chain of trust linking them to sybil attack bitcoin wiki trusted entity, and whether the reputation system treats all entities identically.
As of [update]evidence showed that large-scale Sybil attacks could be carried out in a very cheap and efficient way in extant realistic systems such as BitTorrent Mainline DHT. An entity on a peer-to-peer network is a piece of software which has access to local resources. An entity advertises itself on the peer-to-peer network by presenting an identity.
More than one identity can correspond sybil attack bitcoin wiki a single entity. In other words, the mapping of identities to entities is many to one. Entities in peer-to-peer networks use multiple identities for purposes of redundancy, resource sharing, reliability and integrity. In peer-to-peer networks, the identity is sybil attack bitcoin wiki as an abstraction so that a remote entity can be aware of identities without necessarily knowing the correspondence of identities to local entities.
By default, each distinct identity is usually assumed to correspond to a distinct local entity. In reality, many identities may correspond to the same local entity. An adversary may present multiple identities to a peer-to-peer network in order sybil attack bitcoin wiki appear and function as multiple distinct nodes. The adversary may thus be able to acquire a disproportionate level of control over the network, such as by affecting voting outcomes. In the context of human online communitiessuch multiple identities are sometimes known as sockpuppets.
A notable Sybil attack in conjunction with a traffic confirmation attack was launched against the Sybil attack bitcoin wiki anonymity network for several months in by unknown perpetrators. Validation techniques can be used to prevent Sybil attacks and dismiss masquerading hostile entities.
A local entity may accept a remote identity based on a central authority which ensures a one-to-one correspondence sybil attack bitcoin wiki an identity and an entity and may even provide a reverse lookup. An identity may be validated either directly or indirectly. In direct validation the local entity queries the central authority to validate the remote identities. In indirect validation the local entity relies on already accepted identities which in turn vouch for the validity of the remote identity in question.
Identity-based validation techniques generally provide accountability at the expense of anonymitywhich can be an undesirable tradeoff especially in online forums that wish to permit censorship -free information exchange and open discussion of sensitive topics.
A validation authority can sybil attack bitcoin wiki to preserve users' anonymity by refusing to perform reverse lookups, but this approach makes the validation authority a prime target for attack.
Alternatively, the authority can use some mechanism other than knowledge of a user's real identity - such as verification of an unidentified person's physical presence at a particular place and time - to enforce a sybil attack bitcoin wiki correspondence between online identities and real-world users.
Sybil prevention techniques based on the connectivity characteristics of social sybil attack bitcoin wiki can also limit the extent of damage that can be caused by a given Sybil attacker while preserving anonymity, though these techniques cannot prevent Sybil attacks entirely, and may be vulnerable to widespread small-scale Sybil attacks.
Examples of such prevention techniques are SybilGuard and the Advogato Trust Metric [9] and also the sparsity based metric to identify Sybil clusters in a distributed P2P based reputation system. Alternatively, proof of work can be used to make Sybil attacks more expensive. From Wikipedia, the free encyclopedia. Retrieved 8 February Lecture Notes in Computer Science.
Active attack on Tor network tried to decloak users for five months. Retrieved 10 February This article includes a list of referencesbut its sources remain unclear because it has insufficient inline citations.
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