Macro- and micro-structure of trust networks

TL;DR

This paper analyzes the structure of trust networks using the PGP web of trust, revealing a macro scale-free network with micro strongly-connected cells, and examines their robustness against targeted attacks.

Contribution

It uncovers the coexistence of macro-scale scale-free structures with micro strongly-connected components in trust networks and studies their resilience to attacks.

Findings

The trust network exhibits a macro scale-free topology.

Micro strongly-connected cells are resilient to targeted attacks.

Network disintegration occurs rapidly under intentional attacks.

Abstract

A challenging problem in the social sciences is the characterization of the formation of ``social capital''. It is believed that societies with more social capital are more democratic and economically developed than societies with little social capital. However, social capital is a concept hard to quantify and measure in a ``real-word'' context. Here, we take advantage of an existing "web of trust'' between users of the "Pretty-Good-Privacy" (PGP) encryption algorithm, which is used in digital communication to ``sign'' documents so that the recipient knows for sure who the author is. Our analysis reveals the coexistence in the web of trust of a macro scale-free structure with micro strongly-connected cells in a complex network. We also show that when this network is intentionally attacked the scale-free structure rapidly disintegrates and that the resulting network is partitioned into a large number of small strongly-connected cells that are resilient to the intentional attack.