Compression, Encryption And Hashing Flashcards
Why is file compression used?
To reduce the storage of files on disk
Though disk storage is becoming larger and cheaper, why is reducing file size important?
Its important in the sharing and transmission of data as ISPs impose limits and charges on bandwidth
Why do images on a website need to be compressed?
To enable the web pages to load quickly and for streaming to reduce buffering
What are the two compression techniques that I need to know?
Lossy and lossless
What is the difference between lossy and lossless?
With lossy unnecessary information is removed from the original file while when lossless compresses it retains all information required to replicate the original file exactly
What compression technique does MP3 use?
Lossy, removing frequencies that are too high for most of us to hear and remove quieter sounds that are played at the same time as louder sounds
How much of an MP3 file is compressed under compression?
Around 10% of the original size, meaning that 1 minute of MP3 audio equates to roughly 1MB in size
How is voice compressed over the internet or mobile telephone networks?
Using lossy compression, which shows us the apparent difference between lossy and lossless, that lossy loses data
How does lossless compression work in terms of compression?
Records patterns in data rather than the actual data, giving the computer the ability to reverse the procedure and get the file back to its exact accuracy with no data lost
What would use lossless compression?
Program files, as a lose of a character would result in an error in the program code
What is the disadvantage of lossless compression?
That it results in a larger file than lossy, but one that is significantly smaller than the original
What is Run Length Encoding (RLE)?
Rather than recording every pixel in a sequence, it records its value and the number of times it repeats it, so if there is BBBDDAACCCC that would become 3B2D2A4C
How does dictionary compression work?
The compression algorithm searches through the text to find suitable entries in its own dictionary and translates the messages accordingly
What does dictionary compression also have to be stored with?
With the text dictionary, so that it can compare the symbols and translate them to what they were, making the original message can still be reassembled perfectly
What is encryption?
The transformation of data from one from to another to prevent an unauthorised third party from being able to understand it
What is the original data or message before encryption called?
Plaintext
What is encrypted data known as?
Ciphertext
What is the encryption method or algorithm known as?
Cipher
What us the secret information to lock or unlock the message known as?
Key
What is the difference between the Caesar cipher and the Vernam cipher?
They are polar opposites, the Vernam offers perfect security, while the Caesar cipher is very easy to break with little or no computational power
What is the Caesar cipher also known as?
The shift cipher
what is the Caesar cipher?
A type of substitution cipher and works by shifting the letters if the alphabet along by a given number of characters
How many different possibilities are there for the Caesar cipher?
There are only 26 different possibilities
What is the Vernam cipher?
Invented in 1917 by American scientist Gilbert Vernam, is the only cipher proven to be unbreakable, all others are based on computational security and are theocratically discoverable given enough time, cipher text and computational power
