1.3.1 Compression, encryption and hashing

What are the two types of data compression?

Lossy and Lossless compression.

What is lossy compression?

A method that permanently removes non-essential data to reduce file size.

Give an example of lossy compression.

JPG for images and MP3 for audio.

What is lossless compression?

A method that summarizes patterns in data without permanently removing any information.

What is Run Length Encoding (RLE)?

A basic method of compression that summarizes consecutive patterns of the same data.

How does dictionary compression work?

It spots regularly occurring data and stores it separately in a dictionary, reducing the original data size.

What is the advantage of using a dictionary in compression?

It reduces the amount of data stored while producing some overhead.

What is encryption?

A way of making data unreadable without the means to decrypt it.

What is the Caesar cipher?

A basic type of encryption where letters of the alphabet are shifted by a consistent amount.

What is a brute force attack?

An attempt to apply every possible key to decrypt ciphertext until one works.

What is the Vernam cipher?

An unbreakable encryption method using a truly random sequence as a key.

What is the requirement for the one-time pad in the Vernam cipher?

The key must be truly random, longer or equal to the plaintext, used only once, and destroyed after use.

What is symmetric encryption?

A method where the same key is used for both encryption and decryption.

What is the main security issue with symmetric encryption?

The key must be transferred to the recipient, which can be intercepted.

What is asymmetric encryption?

A method using two related keys: a public key for encryption and a private key for decryption.

What is a hashing function?

a process in which an input (called a key) is turned into a random string of values that are a fixed size

What are the rules of hashing?

• the output of a hash function can’t be reversed to form the key.

• This quality makes hashing useful for storing passwords

• A password entered by a user can be hashed and checked against the key to see if it is correct, but a successful hacker would only gain access to the keys,

• which can’t be reversed to gain the passwords.

What does collision resistance mean in hashing?

Two different inputs should not produce the same output.

What is the avalanche effect in hashing?

Changing a single part of the input should result in a completely different hash.