https://www.youtube.com/watch?v=rALbHDgKEBE&list=PLy_2fgXkPiZt3oJcHalAWy9uhQ3wd2fTV&index=4

https://www.youtube.com/watch?v=X6aTyc1pG8I&list=PLy_2fgXkPiZt3oJcHalAWy9uhQ3wd2fTV&index=5

<aside> 💡

I’m confused about the lectures and their order; I’m sure Dr. Ayman explained this chapter tho and it’s included despite it was lecture 4 or not :)

</aside>

As we discussed earlier, we have two main types of encryption:

• Stream Cipher Encryption
  • Encrypts a digital data stream one bit or one byte at a time
  • Examples: Autokeyed Vigenère cipher, Vernam cipher
• Block Cipher Encryption
  • A block of plaintext is treated as a whole and used to produce a ciphertext block of equal length
  • The majority of network-based symmetric cryptographic applications make use of block ciphers
  • We love $XOR$
  • Typically a block size of 64 or 128 bits is used
  • The ciphertext should be the same size of the plaintext
  • in case of having a data longer then the typical 128 bits ⇒ divide you’re data into smaller blocks and encrypt one by one. And while decryption, divide the cipher text and decrypt it block by block

We’re working with data as bits, we don’t care about it was text, image or whatever

in block encryption, it’s 1 to 1 reversible mapping

A bijection is a mathematical function that maps every unique plaintext input to a unique ciphertext output, and vice versa, without any data loss or overlap.

There are $(2^b)!$ possible distinct mappings. (that’s a lot, yeah)

Before we go further, you should know that all encryption algorithms we discussed so far is Classical old, easy to break… from now on, we will be setting rules and build our way to the Modern encryption algorithms

Diffusion and Confusion

Terms introduced by Claude Shannon to capture the two basic building blocks for any cryptographic system

Shannon wanted to hide the statistical data/information from the ciphertext so he introduced 2 concepts: