CS338 Computer Security
Monday, 23 September 2024

+ What happens when I click an http link in a browser?

    http[s]://example.com/something/document.txt

High-level
    - Retrieve the linked resource

Lower-level
    - Browser parses the link into "http[s]" "example.com" "/something/document.txt"
    - DNS lookup: translate "example.com" into an IP address
    - Perform a TCP handshake
    - **** IF "https":
        holy cow, a huge new handshake: TLS to establish
        shared encryption key and other encryption parameters
    - Sends a TCP packet containing
            GET /something/document.txt HTTP/2.0
            Host: example.com
            User-Agent: whatever
            ???
            [blank line]

    - Server looks for /something/document.txt. If it finds it
        or can construct it, server sends the document back:

            200 OK
            Server: nginx/1.8.2
            Date: ...
            Content-Length: ...
            more headers

            [contents of document.txt]

    - TCP crap
        - Browser sends a TCP ACK for the latest bunch of packets
        - [maybe the server sends a FIN to cut the connection...]

    - Browser shows the contents of document.txt on screen
        [If this were an html file, browser would parse it
        for <link>, <script>, <img> etc. tags and then initiate
        new GET requests for the documents]

+ Questions?
- TCP connection has unique ID 4-tuple
    (client IP, client port, server IP, server port)

+ Burp suite proxy tool lab
- Walk through basics together
- Finish lab

+ base64

+ Tomorrow's assignment

+ Where we're going next
- Symmetric encryption
- Diffie-Hellman key exchange
- Asymmetric encryption
- Public key infrastructure