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+# 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
+
+