5.6: Encryption (Doshi)

Question 1

Symmetric encryption

Answer 1

A single key is used to encrypt and decrypt messages.

Question 2

Why are the keys said to be “symmetric” in a symmetric encryption?

Answer 2

Because the encryption key is the same as the decryption key.

Question 3

The advantage of symmetric encryption

Answer 3

Faster computation and processing.

Inexpensive as compared to asymmetric.

Question 4

Major disadvantage of symmetric encryption

Answer 4

Sharing key with another party.

Question 5

Asymmetric encryption

Answer 5

Involves 2 keys ; private key and public key

Question 6

Encryption and decryption in asymmetric encryption

Answer 6

A message encrypted by private key can be decrypted
only by corresponding public key

A message encrypted by public key can be decrypted
only by corresponding private key

Question 7

The speed of asymmetric encryption and cost

Answer 7

Slower computation and processing that a symmetric encryption. Asymmetric is expensive compared to symmetric

Question 8

The advantage of asymmetric encryption

Answer 8

Each party has its own key to encrypt/decrypt a message

Question 9

Who has access to the SENDER’S PRIVATE key in asymmetric encryption?

Answer 9

Key is available ONLY with SENDER

Question 10

Who has access to the SENDER’S PUBLIC key in asymmetric encryption?

Answer 10

Key is available on PUBLIC DOMAIN. The public key can be accessed by ANYONE.

Question 11

Who has access to the RECEIVER’S PRIVATE key in asymmetric encryption?

Answer 11

Key is available ONLY with RECEIVER

Question 12

Who has access to the RECEIVER’S PUBLIC key in asymmetric encryption?

Answer 12

Key is available on PUBLIC DOMAIN. The public key can be accessed by ANYONE.

Question 13

What are the objectives that keys are used to achieve?

Answer 13

Confidentiality/ Autentication/ Non-repudiation / Integrity

Question 14

Use of key when objective is to maintain Confidentiality

Answer 14

In any given scenario, when objective is to ensure ‘confidentiality’, message has to be encrypted using receiver’s public key

Question 15

Use of key when objective is to ensure Authentication /Non-repudiation

Answer 15

In any given scenario, when objective is to ensure authentication and/or non-repudiation following steps to be performed:

(1) hash (message digest) of the message has to be created
(2) and hash to be encrypted using sender’s private key.

Question 16

Use of key when objective is to ensure Integrity:

Answer 16

In any given scenario, when objective is to ensure ‘Integrity’ following steps to be performed:

(1) hash (message digest) of the message has to be created
(2) and hash to be encrypted using sender’s private key

Question 17

Use of keys when objective is to ensure Confidentiality and Authentication:

Answer 17

In any given scenario, when objective is to ensure ‘confidentiality and authentication’, following treatment is required:

(1) message to be encrypted using receiver’s public key (to ensure confidentiality).
(2) hash of the message to be encrypted using sender’s private key (to ensure authentication/non-repudiation).

Question 18

Use of keys when objective is to ensure Confidentiality ; Authentication and Integrity:

Answer 18

In any given scenario, when objective is to ensure ‘confidentiality and authentication and integrity’, following treatment is required:

(1) message to be encrypted using receiver’s public key (to ensure confidentiality)
(2) hash of the message to be encrypted using sender’s private key (to ensure authentication/non-repudiation and integrity)