SLR 9 - COMPRESSION, ENCRYPTION AND HASHING Flashcards
What is the purpose of compression?
- to reduce the size of the files
- to reduce download time
- to reduce storage requirements
- to make best use of bandwidth
What are the 2 types of compression?
- lossy
- lossless
What is lossy compression?
- a compression algorithm that removes non-essential data from a file leading to a noticeable decrease in accuracy of the data
- data lost is non-recoverable.
What is lossless compression?
- a compression algorithm that retains all the data in the file by only storing the instructions needed to reconstruct the original file
- no data is lost
What are 2 different methods of lossless compression?
- run-length encoding (RLE)
- dictionary coding
What is run-length encoding?
a type of lossless compression where repeated occurrences of the same data (like several pixels of the same colour in an image) are stored as single data values with their counts
What is dictionary coding?
- a type of lossless compression where text is searched for entries that match the entries in a dictionary
- entries are substituted by a unique code which can then be translated
What is encryption?
the process of encoding a message so it can only be read by the sender and the intended recipient
What is Caesar cipher?
letters in the alphabet are replaced by a new letter a fixed distance away from the original letter
What is an issue with Caesar cipher?
- easily decrypted
- susceptible to brute force attacks
What is symmetric encryption?
- an encryption technique where the same key is used to encrypt and decrypt data
- a copy of the key must be transferred between both parties
What is the danger with symmetric encryption?
a message can be cracked by either:
- interception of the key
- duplication of the key production process to acquire a copy of the key
What is asymmetric encryption?
- an encryption technique where a public key available to everyone is used to encrypt the data, and the data is decrypted by the paired private key known only by the recipient
- the keys are generated so anything encrypted with 1 key can be decrypted with the other key (together these keys form key pairs)
Why is asymmetric encryption much more secure than symmetric encryption?
its impossible to derive 1 key from the other
What is Vernam cipher?
What is hashing?
- a one-way transformation of data into an abbreviated form called a hash value
- the hash value is used to validate login credentials like passwords or PINs without revealing the original data to hackers
What is hashing used for?
storing PINs and passwords
