It contains several handshake messages in the beginning with length 0 (no *payload* in TCP, equivalent to no *message* for the Application Layer). Meanwhile the output of the `tcpdump` is updated: You should see the output of the `curl` containing the message in plaintext: Then open another terminal and make a `HTTP GET` request using the command: It allows the user to display TCP/IP and other packets being transmitted or received over a network to which the computer is attached. > () is a data-network packet **analyzer** computer program that runs under a command line interface. To demonstrate how we can *sniff* packets, open a new terminal (Opt+t) in Cloud9, and type the command (the IP refers to my personal EC2 instance). A malicious third party can **sniff** the packets exchanged and used the exchanged information to their advantage (**passive attack**) or tried to **hijack** the connection such as posing as a fake server to the client - tricking the client to give important information to this fake server (**active attack**). One apparent *problem* with our simple server is that it runs on plain HTTP, which means that the *message* (between server and client) **is not encrypted**. *Note: afternoon tea break at your own time*. * Studying common text manipulation tools * 1630-1700 Exercise: introduction to useful tools and **summary** * Adding new cron jobs, listing cron jobs, and deleting them * 1600-1630 Running startup scripts with **cron** * Exercise: writing our own `~/.bash_profile` file
* 1530-1600 **Bash profiles** (*maybe we have time for afternoon tea here*) * Important parameters, special characters
* 1500-1530 Bash script **syntax** familiarisation, **sourcing** scripts and **aliasing** * Exercise on file hardlink and symbolic link * 1430-1500 Various file-related **background** **knowledge**
* 1400-1430 Introduction to **shell scripting** * 1130-1230 Introduction to Transport Layer Security (**TLS**) * 0900-1000 Introduction to **Cryptography** # Fundamentals of Network Security and Trustworthy Applications (Day2-Morning)
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