Introduction to Encryption

Question 1

Define Encryption

Answer 1

The process of scrambling data in an attempt to deem it unreadable by unauthorised subjects.

Question 2

Define Cryptography

Answer 2

The science of writing and ciphering information or messages in a way that attempts to deem them unreadable by anyone other than the intended recipients.

Question 3

Define Steganography

Answer 3

The science of hiding information or messages within other messages. For example, hiding a message within an image.

Question 4

Define Cryptanalysis

Answer 4

The science of analysing encrypted information or messages in an attempt to decrypt them.

Question 5

Define Symmetric Encryption

Answer 5

All parties share a copy of an identical key which is used for both encryption and decryption.

Question 6

What are advantages of Symmetric Encryption?

Answer 6

• Simple
• Fast
• Secure (if key length is long enough)

Question 7

What are some disadvantages of Symmetric Encryption?

Answer 7

• If one key is obtained or broken, all subjects in communication are compromised.
• Distribution of keys adds a risk factor.
• Not scalable since key has to be distributed for every subject added to the communication network. Distributing 100 keys for 100 subjects is very risky and has a high overhead.

Question 8

What is Asymmetric Encryption?

Answer 8

Also known as public key cryptography. All subjects involved in communication have a public and private key pair which are used to encrypt and decrypt messages and information.

Question 9

What are the advantages of Asymmetric Encryption?

Answer 9

• Improves security since it removes the key distribution problem
• Scalable due to no need for key distribution.

Question 10

What are some disadvantages of Asymmetric Encryption?

Answer 10

• Asymmetric encryption incurs more computational cost.
• More complex than symmetric encryption.
• Any subject can masquerade as any other subject (unless certification is used).

Question 11

What is the diagram and formula for the encryption - decryption process?

Answer 11

Dk(Ek(PlainText)) = PlainText

Question 12

For encryption define the following components: alphabet; message space; message; cipher text space; key space.

Answer 12

• Alphabet is a finite space that the message space is a subset of.
• Message space is a subset of the alphabet, and contains all possible messages.
• Message is a subset of the message space.
• Key space is the subset of keys that is being used for encryption / decryption.

Question 13

Write the encryption function in notation. What type of function is it? What components map to each other?

Answer 13

Ee - Encryption function
Bijective function
Maps M to C

Question 14

Write the decryption function in notation. What type of function is it? What components map to each other?

Answer 14

Dd - Decryption function
Bijective function
Maps C to M

Question 15

Which 3 security principles does encryption satisfy?

Answer 15

Confidentiality, integrity and authentication through communication channels.