1.3.1 Compression, Encryption and Hashing

• What is the purpose of compression?

  To reduce storage space required by a file
• Why is compression important for sharing files?

  It allows more files to be transferred quickly
• What is a benefit of downloading compressed files?

  Faster download speeds
• What are the two categories of compression?

  • Lossy compression
  • Lossless compression
• What happens to a file during lossy compression?

  Some information is removed from the file
• How does lossless compression differ from lossy compression?

  Lossless preserves all original information
• What is run length encoding (RLE)?

  A method of lossless compression
• How does run length encoding work?

  It replaces repeated values with one occurrence
• What is the RLE representation of AAAAAABBBBBCCC?

  A6B5C3
• When does run length encoding not work well?

  When there’s little repetition in data
• What is dictionary encoding in lossless compression?

  • Replaces frequently occurring data with an index
  • Compressed data stored alongside a dictionary
  • Original data can be restored using the dictionary
• What must be transferred alongside data compressed using dictionary encoding?

  The dictionary for data restoration
• What is the purpose of encryption?

  To keep data secure during transmission
• What are the two types of encryption methods?

  • Symmetric encryption
  • Asymmetric encryption
• What is shared in symmetric encryption?

  A private key between sender and receiver
• What is a risk of symmetric encryption?

  If the private key is intercepted
• How does asymmetric encryption differ from symmetric encryption?

  It uses a public and a private key
• What is a key pair in asymmetric encryption?

  A public key and a private key
• What happens to messages encrypted with a public key?

  Only the recipient's private key can decrypt
• How can you prove a message was sent by you?

  Encrypt it with your private key
• What is hashing?

  • Process of turning input into a fixed size value
  • Uses algorithms called hash functions
  • Output cannot be reversed to form the key

  
• Why is hashing useful for storing passwords?

  It can't be reversed to reveal passwords
• What is a hash table?

  • Data structure holding key-value pairs
  • Formed from a bucket array and a hash function
  • Used for constant time data lookup
• What happens when two keys produce the same hash?

  A collision occurs
• What should a good hash function provide?

  Low chance of collision and quick calculation
• Why should the output of a hash function be smaller than the input?

  To ensure efficient searching for the hash