Onion Routing

KayakNet uses onion routing to provide anonymity for all network traffic.

What is Onion Routing?

Onion routing wraps messages in multiple layers of encryption, like layers of an onion. Each node in the path can only see the previous and next hop, never the full route.

How It Works

Circuit Building

┌────────┐                                              ┌────────┐
│ Sender │                                              │Receiver│
└───┬────┘                                              └────▲───┘
    │                                                        │
    │  Encrypted for Hop 3                                   │
    │  ┌─────────────────────────────────────────────────┐   │
    │  │ Encrypted for Hop 2                             │   │
    │  │ ┌─────────────────────────────────────────────┐ │   │
    │  │ │ Encrypted for Hop 1                         │ │   │
    │  │ │ ┌─────────────────────────────────────────┐ │ │   │
    │  │ │ │           Original Message              │ │ │   │
    │  │ │ └─────────────────────────────────────────┘ │ │   │
    │  │ └─────────────────────────────────────────────┘ │   │
    │  └─────────────────────────────────────────────────┘   │
    │                                                        │
    ▼                                                        │
┌───────┐          ┌───────┐          ┌───────┐              │
│ Hop 1 │─────────▶│ Hop 2 │─────────▶│ Hop 3 │──────────────┘
└───────┘          └───────┘          └───────┘
Removes one        Removes one        Removes final
layer              layer              layer

Step by Step

1. Sender selects 3 random nodes from the network

2. Sender generates session keys for each hop

3. Message is encrypted in layers:

   • Layer 3: Encrypted with Hop 3's key

   • Layer 2: Encrypted with Hop 2's key

   • Layer 1: Encrypted with Hop 1's key

4. Hop 1 receives, decrypts outer layer, forwards

5. Hop 2 receives, decrypts its layer, forwards

6. Hop 3 receives, decrypts final layer, delivers

KayakNet Implementation

Circuit Parameters

Parameter	Value	Rationale
Hops	3	Balance of anonymity and latency
Circuit Lifetime	10 minutes	Prevent long-term correlation
Key Algorithm	X25519	Fast, secure key exchange
Encryption	ChaCha20-Poly1305	Modern AEAD cipher

Circuit Selection

Nodes are selected to maximize anonymity:

// Pseudocode for node selection
func selectCircuit() []Node {
    // Avoid selecting same node twice
    // Prefer nodes from different subnets
    // Exclude recently used nodes
    // Favor nodes with good reputation
}

Header Format

┌─────────────────────────────────────────────┐
│ Version (1 byte)                            │
├─────────────────────────────────────────────┤
│ Circuit ID (16 bytes)                       │
├─────────────────────────────────────────────┤
│ Next Hop Address (encrypted)                │
├─────────────────────────────────────────────┤
│ Ephemeral Public Key (32 bytes)             │
├─────────────────────────────────────────────┤
│ Encrypted Payload                           │
└─────────────────────────────────────────────┘

Traffic Analysis Resistance

Beyond basic onion routing, KayakNet implements:

1. Constant Packet Size

All packets are padded to 1024 bytes, preventing size correlation.

2. Timing Obfuscation

Random delays (0-100ms) prevent timing analysis.

3. Dummy Traffic

Nodes send fake traffic to obscure real patterns.

4. Traffic Mixing

Packets are batched and shuffled before forwarding.

Anonymity Properties

What Onion Routing Provides

✅ Sender Anonymity - Receiver doesn't know sender ✅ Receiver Anonymity - Sender doesn't know receiver's IP ✅ Relationship Anonymity - Third parties can't link sender/receiver ✅ Forward Secrecy - Past traffic can't be decrypted

What It Doesn't Provide

❌ Global Passive Adversary - Nation-state level monitoring may correlate ❌ Endpoint Compromise - If sender or receiver is compromised ❌ Traffic Confirmation - If adversary controls first and last hop

Compared to Tor

Feature	KayakNet	Tor
Default Hops	3	3
Circuit Rotation	10 min	10 min
Traffic Padding	Yes	Limited
Timing Obfuscation	Yes	No
Dummy Traffic	Yes	No
Directory Servers	No (DHT)	Yes

Performance Impact

Onion routing adds latency:

Metric	Without Onion	With Onion
Latency	~50ms	~150-300ms
Throughput	High	Moderate
CPU Usage	Low	Moderate

The tradeoff is acceptable for privacy-focused applications.

Configuration

# Use 5 hops instead of 3 (not recommended)
./kayakd --onion-hops 5

# Note: More hops = more latency, diminishing returns on security