Lecture 4 - Cryptography Basics

Question 1

What are the ingredients of cryptography?

Answer 1

• plaintext (original text to be encrypted)
• encryption algorithm (substitution and transposition of plaintext)
• secret key (the input to the algorithm)
• ciphertext (algorithm output)
• Decryption algorithm (reverse of the encryption algorithm)

Question 2

Classification of cryptography?

Answer 2

• type of operations used to transform plaintext to ciphertext (are we using substitution or transposition or both) -> information can’t be loss regardless!
• way of processing plaintext (block or stream)
• number of keys used (same or different)

Question 3

What is the difference between block and stream when processing plaintext?

Answer 3

Block processes the input of one block of elements at a time, while Stream cipher processes the input elements continuously (one at a time).

Question 4

What is it called when we are using one key for encryption?

Answer 4

Symmetric encryption

Question 5

What is it called when we are using 2 keys for encryption?

Answer 5

Asymmetric encryption

Question 6

What is symmetric encryption?

Answer 6

Both the sender and receiver have the same key, which can be used for decryption and encryption.

Question 7

What is asymmetric encryption?

Answer 7

This is where the public key used for encryption is publicly available, while the private key is only available to the receiver. Sender encrypts using public, receiver decrypts with private.

Question 8

What is a massive problem with asymmetric encryption?

Answer 8

encryption by private key can be decrypted with the public key, so avoid encrypting with private key as then everyone can decrypt