Tor Network Simulator

This project implements a modular and extensible simulator of the Tor network.
It reproduces the core logic of onion routing, multi-hop circuit formation, relay cell forwarding, and several categories of attacks that target anonymity and network integrity.

Communication occurs locally through TCP sockets.
Each node, client, and server is assigned a symbolic IP address, managed by an internal oracle, which is used for logging, circuit analysis, and attack evaluation.

An interactive interface is included:
each node, client, and server exposes a terminal console where commands can be executed directly.
The interface also displays circuits visually using arrows between nodes, along with symbolic IPs and compromised-node indicators.

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Main Components

• Directory Server – registers nodes and distributes descriptors.
• Client – constructs circuits of three or more hops and forwards traffic.
• Tor Nodes – operate as Guard, Middle, or Exit relays with persistent socket connections.
• External Server – destination for traffic exiting the network.
• Graphical Interface – visualizes node topology, symbolic IPs, and circuits.

All entities run locally and communicate over socket pairs such as (127.0.0.1, port).

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Circuit Construction and Node Selection

The client selects nodes according to a weighted and constrained mechanism inspired by Tor’s consensus.

Weighted Selection Criteria

1. Bandwidth (99.9% of the weight)

• Normal nodes: bandwidth in the range 0–3
• Compromised nodes: bandwidth fixed at 3

Higher bandwidth yields higher selection probability.

2. Uptime (0.1% of the weight)

• Normal nodes: 10–100
• Compromised nodes: 80–100

Uptime provides a mild bias toward stable nodes.

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Diversity Constraints

Node selection enforces multiple diversity rules:

• Owner diversity

  • No two nodes in a circuit may belong to the same owner.
  • Normal nodes come from a pool of 5 owners.
  • Compromised nodes come from 40 owners.

• Subnet diversity

  • Nodes must belong to different /16 subnets, preventing grouping of hops under the same hosting provider or network segment.

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Circuit Axioms

• Guard nodes are reused when already established.
• Middle and Exit nodes must respect all weighting and diversity constraints.
• Circuit length is extendible, allowing more than three hops.

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Implemented Attacks

Multiple attack vectors are implemented, covering both active and passive strategies.

Correlation Attacks

• Timing correlation
• Traffic volume matching
• Statistical inference
• Guard–Exit flow comparison

Compromised nodes log timestamps, packet metadata, and symbolic IP paths.

DoS Attacks

• Circuit flooding via continuous CREATE requests
• Resource exhaustion targeting routing tables or socket pools

Redirection Attacks

• Exit-node redirection to attacker-controlled destinations

Node Compromisation

• Full plaintext inspection after onion-layer removal
• Manipulation of routing behavior
• Logging of circuit metadata

Node Descriptor Falsification

• Bandwidth inflation
• Fake uptime reports
• Manipulation of identity attributes to increase selection probability

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Images