Week 4: Security

Introduction

Keeping people away from things you don’t want them to see
Computers are among the least secure devices you own
- Data or files are stored on them as 0s and 1s
  - Can be financial info, photos, etc.

What does it mean to delete a file off of a hard drive?
- Visually, it disappears from a desktop or folder
Files are stored on a computer as 0s and 1s
Some space needs to be allocated for the file
The operating system has a file that keeps track of files and their location on the disk
Graphically, when a file is deleted, it moves to the trash (or recycle bin)
- It can still be easily revived from here until you empty the trash
However, an operating system doesn’t delete it from the hard drive
- It simply forgets the location and existence of the file!
- One can theoretically recover data by looking for familiar patterns of bits
So how do we delete more securely?
- Re-saving a file with overridden information actually could not override the old bits but rather create more 0s and 1s stored on a hard drive!
- Special software can wipe data off of a hard drive
Who do computers have this obvious flaw with deleting?
- What if we accidentally delete a file?
  - This structure allows for recovery
- Wiping data also takes a lot of time, so it’s much faster to just forget the locations of the data

A feature supported by HTTP
Little values a web server puts on a user’s browser
Used to remember if a user has visited a website before
- Allows you to not have to log in every time you visit or refresh a page
  - When you log into a web server, a cookie is planted on your browser
- Stored in a database
- The browser will send value to the webserver to remind of the previous login
When we make a request we send:

GET / HTTP/1.1 Host: example.com
We receive:

HTTP/1.1 200 OK Set-Cookie: session=29823bf3-075a-433a-8754-707d05c418ab
- The server gives us a cookie.