SLR 9 Flashcards
Compression
What is the purpose of compression?
-Reduce the size of files
-Reduce download times
-Reduce storage requirements
-Make best use of bandwidth (time it takes to be transmitted to others)
What are the two types of compression?
Lossy and lossless
How does lossy compression work?
Data in a file is removed and can not be recovered
(However, very little is lost so it’s okay for images, but bad for text files)
How does lossless compression work?
Uses an algorithm to shrink a files size without losing important data
What are the two types of lossless compression?
-Run-length Encoding (For images)
-Dictionary encoding (For text)
How does dictionary encoding compression work for text files?
It builds an index which we can visualise as a table, by referencing different words on the table with different numbers
How does run length encoding compression work for images?
With a black and white image, 0 would be white and 1 would be black
It would be stored somewhat like this: 22 white pixels followed by, 6 black pixels followed by… 8 white pixels…. and repeat
What is Encryption?
The process of encoding a message so it can be read only by the sender and intended recipient
How does Symmetric Encryption work?
A single key is used to encrypt and decrypt a message, meaning both parties need to know the key
What are the dangers of Symmetric Encryption?
The key can be intercepted by a hacker or they could duplicated the key during the process, allowing them to decrypt private messages
This is why Asymmetric Encryption is used for processes such as sending bank card information
How does Asymmetric Encryption work?
Uses two separate keys, Key A encrypts a message and Key B decrypts it
This is better than Symmetric Encryption because Key A and Key B aren’t the same, and it’s practically impossible to derive one key from another, making a much more secure connection
What are the keys in Asymmetric Compression called
Key A and B are called Key Pairs. One key of the pair need to be picked as a public key and a private key
What is the difference between a public and private key?
A public key can be made public and can be published online
The private key is also used to decrypt messages encrypted by a public key
How is Hashing different to encryption?
Hashing is irreversable, which compression isn’t