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\[ \newcommand{\peers}{\mathcal{P}} \]

Peer Management Protocol#

Definitions#

A peer is a pair consisting of addr (IPv4/6 address) and port (port number).

A peer management structure is a tuple, (G, B, C), where:

  • G represents the set of good peers,
  • B stands for the set of banned peers,
  • C signifies the set of connected peers.

This structure adheres to the following conditions:

  • Good peers (G) and banned peers (B) are disjoint: \(G \cap B = \emptyset\).
  • Connected peers (C) are a subset of good peers: \(C \subseteq G\).
  • Good peers (G) and banned peers (B) are subsets of all peers: \(G \subseteq \peers\), \(B \subseteq \peers\).

Peer Penalization and Blacklisting#

A penalty is a tuple descr, score, where descr describes misbehaviour, and score is the penalty score that signifies the degree of misbehaviour.

There are four categories of penalties:

  • NonDeliveryPenalty: Applied when a peer fails to deliver the requested modifier within the stipulated time frame.
  • MisbehaviorPenalty: Applied when a peer delivers an invalid modifier.
  • SpamPenalty: Applied when a peer delivers a non-requested modifier.
  • PermanentPenalty: Levied on peers who deviate from the actual network protocol.

When a penalty is imposed, the penalized peer is added to the penalty book. A penalty book is a mapping ip -> (score,ts), where ip represents a peer IP address, score signifies the accumulated penalty score, and ts is the timestamp of when the peer was last penalized.

Penalties of type NonDeliveryPenalty, MisbehaviorPenalty, and SpamPenalty are not imposed on the same peer repetitively within a specified safe interval. A safe interval refers to the delay between the application of penalties.

When a peer accumulates a critical penalty score, it gets added to the blacklist. A blacklist is a mapping ip -> ts, where ip stands for a peer IP address and ts represents the timestamp when a peer is banned.

The application of PermanentPenalty is immediate and results in the permanent ban of the peer.

Peer Discovery#

The peer discovery protocol seeks new peers from a source and introduces them to the set of good peers, G. The source could be another peer, a trusted central server, or an untrusted communication channel such as IRC, Twitter, etc.