Studied by 3 people
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
