ICT Encryption Lecture

TEST 4

What is Encryption?

Encryption is the process of converting readable data — called plaintext — into an unreadable format called ciphertext — in order to protect information from unauthorised access. It matters because it protects sensitive data

What are the key components of a cryptosystem?

A cryptosystem consists of six components: (1) Plaintext — the original readable message anyone can understand (2) Ciphertext — the unreadable output produced after encryption (3) Encryption Algorithm — converts plaintext into ciphertext by taking two inputs: the plaintext and an encryption key (4) Decryption Algorithm — the reverse process that converts ciphertext back into plaintext using a decryption key (5) Encryption Key — the value used by the sender to convert plaintext into ciphertext (6) Decryption Key — the value used by the receiver to convert ciphertext back into plaintext

What are the types of encryption and how do Symmetric and Asymmetric differ?

The three types of encryption are: (1) Symmetric Encryption — uses the same key for both encrypting and decrypting data — example: AES (Advanced Encryption Standard) (2) Asymmetric Encryption — uses a public key to encrypt and a separate private key to decrypt — example: RSA (Rivest-Shamir-Adleman) (3) Classical Ciphers — older simpler methods such as the Caesar Cipher and Shift Cipher used primarily for learning

What is a Shift Cipher and how does it work?

A shift cipher is a classical encryption technique where each letter in the plaintext is shifted by a fixed number of positions in the alphabet. Encryption formula: Ci = (Pi + s) mod 26 — where Pi is the letter's position

What is the Caesar Cipher and what are its limitations?

The Caesar Cipher is a specific type of shift cipher named after Julius Caesar who used it to send secret messages. It works by shifting each letter by a fixed value — for example a shift of 3 turns HELLO into KHOOR. Its limitations are: (1) it is easy to break through pattern analysis (2) it has a very limited key space of only 25 possible shifts (3) it is not secure for any modern application

What is a Transposition Cipher and how does it differ from a Substitution Cipher?

A transposition cipher encrypts a message by rearranging the positions of characters according to a system — without changing the actual characters themselves. Unlike substitution ciphers which replace letters with different ones