1.3.1 Compression, Encryption, Hashing

loseless compression

reduces the file size that when it is decompresses all the data is retrieved. does this by recording patterns in the data rather than the actual data.

use of lossless

code, text, architercural plans

lossy compression

removes all non-essential data. reduces a file size such that when decompressed some data is lost

use of lossy

colour depth reduction, resolution reduction

example of lossy compression

MP3 format file is 10% smaller than original, quiet sounds and high frequencies are cut out

2 examples of lossy compression

voice transmission, mp3

run length encoding and dictionary encoding are 2 types of …

lossless compression

run length encoding

compression where data is stored as frequency data pairs.

what is compression?

the process of reducing space needed to store a file

what is a frequency data pair?

single instance of a pattern and how many repetitions of the pattern

con of dictionary encoding

not useful for smaller bodies of text as it requires text in dictionary to be stored.

con of RLE

doesn’t work well for Digital images because the repetitions aren’t frequent.

plaintext

the original data

ciphertext

encrypted data

cipher

encryption method

key

information needed to lock or unlock the data

encryption

transformation of data from plaintext to cipher text to protect sensitive data

encryption is two-ways meaning that data can be resorted into its original form, still requires and encryption key.

symmetric encryption

private key

conditions of symmetric encryption

same key used to encrypt and decrypt text

cons of symmetric encryption

less secure key exchange means that high likelihood that any interception leads to cipher text being decrypted.

conditions for asymmetric encryption

uses two separate and indistinguishable keys; public key for encryption; private key to decrypt.

What is the purpose of compression

Reduce size, download time and storage requirements. Make best use of the bandwidth.

what is a hashing algorithm?

a mathematical function that garbles data and makes it unreadable. used in data storage and security for protecting sensitive information.

what are 2 key properties of hashing algorithms ?

consistency-same input produces the same hash. sensitivity - minor changes produce completely different hash

Name three common hashing algorithms

MD5 SHA-1 SHA-256

What are the characteristics of a good hash?

Easy to calculate, few collisions and provides an output smaller than the input.

what is hashing?

hashing is a one-way non-reversible mathematical process that produced an value from the input value