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1.3.1 compression, encryption and hashing (systematic and asymmetric…
1.3.1 compression, encryption and hashing
lossy and lossless comprssion
compression
reduce download dtime
reduce file storage
make best use of bandwidth
lossy
data is remvoed
data that is not important is stripped
cannot be restored
media files
jpeg,mp3,mpeg etc
lossless
actule data is removed byt it is ecoded in a way that it can be restored
computer program or text document
less effective
can be restored
zip,GIF,PNG
trade off between quality and processing power
types of less less comprestion
run lengeth
redudent repeating data
store item once then how its repeated
e.g black pixel for 100 pixels
remove white space
dictionary
index is made
every data item is recorded
refrances used instead of orginal
only works with repeated data
systematic and asymmetric encryptionn
encoding a message so it can only be read my sender and resipiant
casar cipher shifts
symetic
same key encrypt and decrypt
both partyes need to know the key
need to be kept secret
or uniqly genrated
key could be intcepted
not secure anouth
asymmetric encyrption
two different keys one to encrypt one to decrypt
key pairs
one of the keys is public one private
the public key is used the encrpyt freely
key server
but only you and your prvert key can decrypt
A and B want to commuicate, A combines there privert key with Bs public key and sends a message B then decrypts using As public key and Bs privert key
proves identity
image
keys are large random number
hashing
trandofrms data item
genrating disak adressin on Random acess
storing and checking passwowrds
passwords are not stored in plain text
impossible to reverse
hashed straight away so password never known
converted again
looked up