1.3.1 - Compression, Encryption and Hashing Flashcards
Where is compression important?
The sharing and transmission of data. Images on websites need to be compressed so they load quickly.
How does lossy compression work?
By removing non-essential information.
What is a disadvantage of lossy compression?
Quality decreases.
How does lossy compression work on audio?
The highest and lowest frequencies that most people can’t hear are removed.
How does lossless compression work?
By recording patterns in the data then removing them. It then provides a set of instructions with how the file should be reassembled.
Which compression method results in a bigger file?
Lossless.
What is RLE and what does it do?
A form of lossless compression. In an image RLE records a value (pixel) and the number of time it repeats rather than every pixel.
How does dictionary based compression work?
Sends an index of a word stored in a dictionary instead of sending the words which results in less data sent but the whole text can be rearranged.
What is encryption and why is it used?
The transformation of data from one form to another to prevent unauthorised people from being able to understand it.
What is the original data before encryption called?
Plaintext.
What is the encrypted data called?
Cipher-text.
What is a cipher?
An encryption method.
How does the Caesar cipher work?
By shifting indexes of letters in the alphabet.
