From 0c526a4983d6fb760fdfb92fd1330bf3fad33176 Mon Sep 17 00:00:00 2001
From: Trance-0 <60459821+Trance-0@users.noreply.github.com>
Date: Fri, 23 Jan 2026 12:26:56 -0600
Subject: [PATCH] updates

---
 content/CSE4303/CSE4303_L3.md |  2 +-
 content/CSE4303/CSE4303_L4.md | 27 +++++++++++++++++++++++++++
 content/CSE4303/_meta.js      |  2 ++
 3 files changed, 30 insertions(+), 1 deletion(-)
 create mode 100644 content/CSE4303/CSE4303_L4.md

diff --git a/content/CSE4303/CSE4303_L3.md b/content/CSE4303/CSE4303_L3.md
index d6a921c..f1dd44c 100644
--- a/content/CSE4303/CSE4303_L3.md
+++ b/content/CSE4303/CSE4303_L3.md
@@ -31,7 +31,7 @@ Domain names for the application/human layer
 
 - E.g., www.wustl.edu
 
-![TCP Protocol Stack](https://notenextra.trance-0.com/CSE4303/TCP-protocol-stack.png)
+![TCP Protocol Stack](https://notenextra.trance-0.com/CSE4303/TCP-protocal-stack.png)
 
 ![Data Formats](https://notenextra.trance-0.com/CSE4303/Network-data-formats.png)
 
diff --git a/content/CSE4303/CSE4303_L4.md b/content/CSE4303/CSE4303_L4.md
new file mode 100644
index 0000000..3e6c060
--- /dev/null
+++ b/content/CSE4303/CSE4303_L4.md
@@ -0,0 +1,27 @@
+# CSE4303 Introduction to Computer Security (Lecture 4)
+
+## Network attacks
+
+### Examining the transport layer
+
+#### Transmission Control Protocol (TCP)
+
+Connection-oriented, preserves order
+
+- Sender
+  - Break data into packets
+  - Attach packet numbers
+- Receiver
+  - Acknowledge receipt; lost packets are resent
+  - Reassemble packets in correct order
+
+#### Security Problems
+
+1. Network packets pass by untrusted hosts
+   - Eavesdropping, packet sniffing
+   - Especially easy when attacker controls a machine close to victim (e.g. WiFi routers)
+2. TCP state easily obtained by eavesdropping
+   - Enables spoofing and session hijacking
+3. Denial of Service (DoS) vulnerabilities
+
+
diff --git a/content/CSE4303/_meta.js b/content/CSE4303/_meta.js
index ce40348..894f7e5 100644
--- a/content/CSE4303/_meta.js
+++ b/content/CSE4303/_meta.js
@@ -6,4 +6,6 @@ export default {
     CSE4303_L1: "Introduction to Computer Security (Lecture 1)",
     CSE4303_L2: "Introduction to Computer Security (Lecture 2)",
     CSE4303_L3: "Introduction to Computer Security (Lecture 3)",
+    CSE4303_L4: "Introduction to Computer Security (Lecture 4)",
+
 }