Compression, Encryption and Hashing(Not done)

Question 1

Why do we need compression?

Answer 1

Data transmitted across the internet needs to be compressed where possible

Question 2

Why do you need to compress(reduce) files?

Answer 2

Reduce download times
Make the best use of bandwidth
Reduce file storage requirements

Question 3

What is lossy compression?

Answer 3

Some data is stripped out to reduce file size.The data removed is chosen to have the least importance.
Lossy is typically used in image and video files and music files,where it is less likely to be noticed by human observation
Files compressed by lossy methods cannot be reinstated to their original detail
Examples:JPEG,MPEG,MP3

Question 4

What is Lossless compression?

Answer 4

Some files must not be degraded,for example a compute rprorgam will not work correctly if data is removed from it
Lossless reatins all data by encoding it
The orginal file can be regernated

Question 5

What is dictionary encoding?

Answer 5

The compression algorithm builds index where each data item is recorded along with an index refernce,the compressed file then consists f teh dictionary plus the sequence of occurences

Question 6

What is run-length encoding?

Answer 6

This makes use of redundant data so that if a data item occurs multiple times, the item in an index along with the number of repetitions.For example, part of an image with many adjacent blue pixels could be stored in an index by storing the start location and the number of repetitions

Question 7

What is symmetric encryption?

Answer 7

Uses the same key to encrypt and decrypt data.

Question 8

What is asymmetric encryption?

Answer 8

Uses two separate but related keys, one key is made public so that others wishing to send you data can use this to encrypt the data.(This key cannot decrypt data)The Other is know only by you and only this can be used to decrypt the key