Computer Science

Cryptography
1. Cryptography is derived from the Greek word 'kryptos' which means hidden or secret it is also the art of writing or solving codes
2. Ceaser Cipher
  1. Julius Ceasar developed the first modern cipher. It is known as the 'Ceasar Cipher'. Each character in the message is replaced by the Character three positions ahead of it in the alphabet
    1. Julius Ceasar might have encrypt messages his messages so he could send messages to his troop and even if the messages were caught his enemies wouldn't understand the message
    2. Disadvantages on using the Caesar Cipher
      1. -The Person using it has to be able to understand how to decrypt it
        -Ceasar Ciphers are easy to break/crack
        -It doesn't allow for numbers or symbols
3. Bar codes
  1. The supermarkets computers holds a database containing information on all the products sold in the store. As the items are scanned the bar code number is passed to the computer where a search is made of the database. As soon as the number is matched with the data held in the computer, the price and description are matched back till where the costumers itemised receipts is printed
  2. The bar codes can be read with a hand-held scanner or the laser scanner at the checkout. The scanner emits a beam of light that reflects off the bar code. The white lines reflect the light strongly while the black lines reflects less strongly. These variations in the reflections are picked up by sensensors in the scanner and converted into a digital signal
  3. Making sense of the bar codes
    1. 1st 2 number- represents the country origin
      1. Next five-Manufactures number
        Next five- product code
        Last number- Called the 'check digit' or 'check sum' and it's calculated from the other numbers to confirm the whole number has been read correctly
4. E-commerce
  1. Ecommerce means the sales and purchases of goods and services over over electronics systems such as the internet
  2. SSL, Private Key and Public Key Encryption
    1. -Web browers (e.g. Internet explorer) security technology
      1. -Allows confidential data (e.g. credit card) to pass from your computer to an interner server
        -If a website is using a Secure Socket Layer, it will encryot your credit card info
        The 'lock' is the public key
        The 'key; is the private key
  3. Data rights management
    1. DMR is used to restrict the ability to make copies of electronic media such as music, films, soft ware and games
      1. Until recently, almost all music which could be purchased and downloaded via the internet was protected by DRM
        The DMR protected music could be sold, downloaded and played on a set number of computers and portable devices
Python Programming
1. Python can be used in 2 modes:
  1. -Interactive mode = let you see your results as you type them
    1. -Script mode = lets you save your program and run it again later
2. Data Types
  1. We can't do much program without the using some data. Each piece of data has a type:
    1. -Interger (int) = a whole number
      1. -Floating point number (float) = a decimal number
        -String (str) = one or more letters, number, punctuation etc. written together "in quotes"
        -Boolean = true or false
3. Variables
  1. One of the most important features of any programming language is the ability to store data inside variables. A variable is like a storage box- you can store something inside it, and you can give it a name by which you can refer it to later
4. Comparative Operators
  1. == equal to/equivalent of less than
    1. < less than
      1. > greater than
        >= greater than or equal to
        <= less than or equal to
App inventor
1. Smartphone software
  1. All of these technologies would be useless without software to bring together. Software is the name for computer programs-list of instructions- which tells the computer hardware how to perform a task..
    1. On mobile devices, there are two main pieces of software:
      1. -The operating system
        -Apps
2. Operating System
  1. An operating system(OS) is a aset of programs that a computer runs all the time it is switched on. AN OS performs many tasks, but we can think of it as the program that gets the computer "up and running" and makes it work and look the way it is. Examples of OS on desktop computers include Microsoft, Window, Apple MacOS and linux
3. Component designer
  1. -Palette = holds the components you can use in your program, separated into categories.
    1. -Viewers = lets you arrange components on a rough preview of the phone screen
      1. -Components = lists components in the app
        -Media = lists media files for the app
        -Properties = of selected component

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