Encryption

Question 1

What is encryption?

Answer 1

The process of converting plaintext into ciphertext, which cannot be understood without the key to decrypt it.

Question 2

What is plaintext?

Answer 2

Data in human-readable form.

Question 3

What is ciphertext?

Answer 3

Data that has been encrypted.

Question 4

What is symmetric encryption?

Answer 4

Encryption that uses the same key to encrypt and decrypt.

Question 5

What is asymmetric encryption?

Answer 5

Encryption that uses different keys to encrypt and decrypt.

Question 6

What is Caesar Cipher?

Answer 6

A substitution cipher where one character of plaintext is substituted for another, which becomes ciphertext.

Question 7

What are the limitations of Caesar Cipher?

Answer 7

Caesar Cipher is computationally insecure. This is because letter frequency analysis can be used to determine the shift and there are only 25 possible different shifts.

Question 8

What do all encryption techniques suffer from?

Answer 8

The key exchange problem.

Question 9

What is the key exchange problem?

Answer 9

We need to send the key to the recipient without anyone intercepting it.

Question 10

What is a solution for the key exchange problem?

Answer 10

The one time pad.

Question 11

What is the one time pad?

Answer 11

A key that is only used once to encrypt and decrypt a message, then it is discarded.

Question 12

What is the Vernam Cipher?

Answer 12

It is a cipher that uses a one time pad. It’s more secure than Caesar Cipher and involves XOR operations.

Question 13

How does Vernam Cipher work?

Answer 13

A key is created of entirely random characters that are the same length as the message.

For each character in the message and the key, traditionally the 5-bit Baudot Code is used to convert the character into binary.

Question 14

What is computational hardness?

Answer 14

The degree of difficulty in cracking a code.

Question 15

What are the conditions for perfect security in Vernam?

Answer 15

• The key must be truly random
• The key length must be at least the same as the plaintext length
• The key must only be used once then discarded (one time pad)
• The key must only be shared with the intended recipient