🔐 TLS & Mutual TLS (mTLS) Analysis over Layer-3 Routing using Linux Network Namespaces

---

🚀 Motivation

This project was built to deeply understand how TCP and TLS operate over a routed Layer-3 network.

Instead of using physical hardware, Linux network namespaces were used to simulate:

• Isolated network nodes (client, router, server)
• Two different IP subnets
• IP forwarding across a software router
• Real packet-level protocol behavior

The objective was to analyze:

• TCP 3-way handshake
• TLS 1.2 handshake workflow
• Certificate exchange in plaintext
• Encryption boundary after ChangeCipherSpec
• TTL decrement across a router (Layer-3 proof)

This project was later extended to include Mutual TLS (mTLS) to demonstrate two-way authentication, where both client and server verify each other's identity using certificates.

This project provides a hands-on, packet-level understanding of secure communication mechanisms used in modern distributed systems and zero-trust architectures.

---

🗺 Network Topology

Addressing Scheme

Namespace	Interface IP	Subnet
red (Client)	10.0.1.2	10.0.1.0/24
router	10.0.1.1 / 10.0.2.1	Two connected subnets
blue (Server)	10.0.2.2	10.0.2.0/24

• Default gateway (red): 10.0.1.1
• Default gateway (blue): 10.0.2.1
• IP forwarding enabled in router namespace

---

🧰 Requirements

• Ubuntu 22.04 (or compatible Linux system)
• iproute2
• OpenSSL
• tcpdump
• Wireshark (host machine)

---

⚙️ Setup Instructions

🔐 Generate Certificates

./generate_certs.sh

🌐 Create Namespaces and Routing

sudo ./setup.sh

🔎 Verify Connectivity

sudo ip netns exec red ping 10.0.2.2

Expected observation:

• Successful ping replies
• TTL decreases from 64 → 63 (proof of router traversal)

🧹 Cleanup

sudo ./cleanup.sh

---

🔐 TLS Handshake Execution & Packet Capture (TLS 1.2)

This section demonstrates capturing and analyzing the TLS handshake at packet level in a clean, linear workflow.

🛠 Step 1 — Start Packet Capture (Router)

sudo ip netns exec router tcpdump -i any port 4433 -w tls_capture.pcap

Keep this running.

---

🔐 Step 2 — Start TLS Server (blue namespace)

(Open a new terminal)

sudo ip netns exec blue openssl s_server \
-accept 4433 \
-cert /certs/server.crt \
-key /certs/server.key \
-tls1_2

Expected output:

ACCEPT

---

🔗 Step 3 — Start TLS Client (red namespace)

(Open another terminal)

sudo ip netns exec red openssl s_client \
-connect 10.0.2.2:4433 \
-CAfile /certs/ca.crt \
-tls1_2

This initiates the TLS handshake.

---

🛑 Step 4 — Stop Packet Capture

Press:

Ctrl + C

in the tcpdump terminal.

---

👀 Step 5 — Analyze in Wireshark

Open the generated .pcap file in Wireshark.

---

🔍 Recommended Filters

tls
tcp.port == 4433

---

🔎 Key Observations (TLS)

• TCP 3-way handshake occurs before TLS begins
• TLS handshake messages visible:
  • ClientHello
  • ServerHello
  • Certificate
  • ServerHelloDone
  • ClientKeyExchange
• Encryption starts after ChangeCipherSpec
• Subsequent packets appear as:

  TLS Application Data
  

---

🔐 Mutual TLS (mTLS) Execution & Packet Capture

This section demonstrates mutual authentication where both client and server verify each other using certificates.

🛠 Step 1 — Start Packet Capture (Router)

sudo ip netns exec router tcpdump -i any port 4433 -w mtls_capture.pcap

Keep this running.

---

🔐 Step 2 — Start mTLS Server (blue namespace)

sudo ip netns exec blue openssl s_server \
-accept 4433 \
-cert /certs/server.crt \
-key /certs/server.key \
-CAfile /certs/ca.crt \
-Verify 1 \
-tls1_2

---

🔗 Step 3 — Start mTLS Client (SUCCESS CASE)

sudo ip netns exec red openssl s_client \
-connect 10.0.2.2:4433 \
-cert /certs/client.crt \
-key /certs/client.key \
-CAfile /certs/ca.crt \
-tls1_2

Expected result:

• Handshake succeeds
• Client and server authenticate each other

---

❌ Step 4 — Negative Test (Without Client Certificate)

sudo ip netns exec red openssl s_client \
-connect 10.0.2.2:4433 \
-CAfile /certs/ca.crt

Expected result:

• Handshake fails
• Server rejects client

---

🛑 Step 5 — Stop Packet Capture

Press:

Ctrl + C

in the tcpdump terminal.

---

👀 Step 6 — Analyze in Wireshark

Open the generated .pcap file in Wireshark.

---

🔍 Recommended Filters

tls
tcp.port == 4433

---

🔎 Key Observations (mTLS)

• Server sends Certificate Request
• Client responds with its Certificate
• Client proves identity using Certificate Verify
• Mutual authentication is established
• Without client certificate → handshake failure

---

🔐 Encryption Boundary

After ChangeCipherSpec, Wireshark shows:

TLS Application Data

This applies to both TLS and mTLS, indicating the transition from asymmetric to symmetric encryption.

---

🌐 Layer-3 Routing Proof

Initial TTL: 64
Observed TTL: 63

---

🔄 TLS vs mTLS Comparison

Feature	TLS	mTLS
Server Authentication	✅	✅
Client Authentication	❌	✅
Certificate Exchange	One-way	Two-way
Security Level	High	Very High
Use Cases	HTTPS	Zero Trust, Microservices

---

📁 Project Structure

network_namespaces/
│
├── blue_namespace/
│ ├── server.crt
│ ├── server.key
│ └── ca.crt
│
├── red_namespace/
│ ├── client.crt
│ ├── client.key
│ └── ca.crt
│
├── ca/
│ ├── ca.crt
│ └── ca.key
│
├── diagrams/
│ └── topology.png
│
├── screenshots/
│
├── report/
│ └── report.pdf
│
├── setup.sh
├── cleanup.sh
├── generate_certs.sh
├── README.md
├── tls_capture.pcap
└── mtls_capture.pcap

---

⚠ Security Disclaimer

Self-signed certificates are used for educational purposes only.

---

🎓 Learning Outcomes

• Layer-3 routing using namespaces
• TCP handshake understanding
• TLS 1.2 internals
• Mutual TLS (mTLS) authentication
• Certificate Authority (CA) concepts
• Packet-level analysis with Wireshark

---

🔗 Lecture Source: Network Namespaces - Session 1

https://nitkeduin-my.sharepoint.com/:v:/g/personal/tahiliani_nitk_edu_in/EZsxo6VafiBIn3ybNUNOYPYBJ9Oe7nvBMFc81vTTC-FhtQ?e=b16yGn

---

👨‍💻 Author

Samyak Gedam
National Institute of Technology Surathkal, Karnataka
Built as part of first task in mini-project course during my 2nd Semester.