3.6 - Data Compression & Encryption Flashcards
What does reducing file size help?
- data is sent more quickly
- less bandwidth
- buffering is less likely
- less storage is required
What is lossy compression? Which file types?
Non - essential data is permanently removed
JPEG, MP3, MP4
What is lossless compression? Which file types?
Patterns in the data are spotted and summarised in a shorter format without permanently removing any information
PNG, GIF, ZIP
When would you use lossy compression?
- need a significantly smaller file size
- not essential to fully recover all the data
- data has random elements so lossless won’t significantly reduce the file size
- contains irrelevant data that can be removed
How does lossy compression work in JPG, MP3?
JPG - removes data permanently and tries to reconstruct an image without the missing data
MP3 - removes sound in the frequency ranges we can’t easily hear or least affect the perceived playback quality. Quieter notes played at the same time as louder sounds are a,so removed
What is run length encoding (RLE)?
Basic method of compression that summarises consecutive patterns of the same data
Works well with sound and image data
What is dictionary compression?
Spots regularly occurring data and stores it separately in a dictionary
What is the Caesar cipher?
Most basic type of encryption and most insecure
Letters of the alphabet are shifter by a consistent amount
What is a frequency analysis? Which encryption method is vulnerable to it?
Looks at how often certain characters or sequences of characters appear to discover patterns and discover the key without doing any brute force attacks
Caesar cipher (max 25 brute force attacks)
What is a brute force attack?
Attempts to apply every possible key to decrypt ciphertext until one works
How does the vernal cipher work?
Uses a one-time pad which is random and used only once then destroyed
Look at flipped learning notes
