Writing an exam answer about encryption

Name:

Date:

Class:

Quick Questions

Shade in the A or B circle for each question.

1. Which sentence is worth a mark for why data is encrypted?

A So that the data cannot be intercepted

B So that if the data is intercepted, it cannot be understood

2. Which answer uses the key terms correctly?

A Plaintext is encrypted using a key to produce ciphertext

B Ciphertext is encrypted using a key to produce plaintext

3. Describing symmetric encryption: which is correct?

A The same key is used to encrypt and to decrypt the data

B One key encrypts the data and a different key decrypts it

4. Describing asymmetric encryption: which is correct?

A A public key and a private key are used as a pair

B Both people keep one identical secret key

5. Which step is correct for sending a secure message with asymmetric encryption?

A Encrypt with the recipient's private key

B Encrypt with the recipient's public key

Match the Pairs

Draw a line connecting each item on the left to its match on the right.

Left column		Right column
1plaintext + key → ciphertext		Aplaintext + shared key → ciphertext → plaintext + shared key
2ciphertext + key → plaintext		Bencrypt(public key) → send → decrypt(private key)
3Asymmetric steps in order: the sender encrypts with the recipient's public key, and the recipient decrypts with their private key		CWrong key. In asymmetric encryption the sender encrypts with the recipient's public key. The private key is used to decrypt and is kept secret.
4Symmetric steps in order: the same secret key is used to encrypt the plaintext and to decrypt the ciphertext		DEncryption in an exam answer: the original readable data is scrambled using a key to make unreadable ciphertext
5The sender encrypts the message with the private key		EDecryption in an exam answer: the unreadable ciphertext is turned back into readable plaintext using the correct key
6Encryption stops hackers from intercepting the data		FEncryption does not stop interception. A hacker can still capture the data, but it is ciphertext, so it is unreadable without the key.

Definitions

plaintext, key, ciphertext

Fill in the Blanks

Complete each line of code by filling in the missing parts.

ciphertext ← ENCRYPT(_________, key)

ciphertext ← ENCRYPT(plaintext, key) plaintext ← _______(ciphertext, key)

ciphertext ← ENCRYPT(plaintext, _________)

ciphertext ← ENCRYPT(plaintext, publicKey) plaintext ← DECRYPT(ciphertext, __________)

Encryption does not stop ____________ but ciphertext cannot be read without the key

Spot the Error

Shade in the letter of the line that contains an error.

Question 1

A Symmetric encryption answer

B Plaintext is encrypted by key

C This produces ciphertext

D A different key decrypts it

Question 2

A Asymmetric answer

B Sender gets the public key

C Plaintext is encrypted with it

D Public key decrypts it

Question 3

A Why encrypt data?

B Packets can be intercepted

C Encryption stops interception

Question 4

A Sending a secure message

B Get the recipient's public key

C Encrypt with your private key

D They decrypt with private key

Question 5

A Symmetric key problem

B Both sides need the same key

C Sharing the key is always safe

D Key thief could decrypt data

Answer Key

Writing an exam answer about encryption

Section A: Quick Questions

B — So that if the data is intercepted, it cannot be understood

A — Plaintext is encrypted using a key to produce ciphertext

A — The same key is used to encrypt and to decrypt the data

A — A public key and a private key are used as a pair

B — Encrypt with the recipient's public key

Section B: Match the Pairs

plaintext + key → ciphertext → Encryption in an exam answer: the original readable data is scrambled using a key to make unreadable ciphertext

ciphertext + key → plaintext → Decryption in an exam answer: the unreadable ciphertext is turned back into readable plaintext using the correct key

Asymmetric steps in order: the sender encrypts with the recipient's public key, and the recipient decrypts with their private key → encrypt(public key) → send → decrypt(private key)

Symmetric steps in order: the same secret key is used to encrypt the plaintext and to decrypt the ciphertext → plaintext + shared key → ciphertext → plaintext + shared key

The sender encrypts the message with the private key → Wrong key. In asymmetric encryption the sender encrypts with the recipient's public key. The private key is used to decrypt and is kept secret.

Encryption stops hackers from intercepting the data → Encryption does not stop interception. A hacker can still capture the data, but it is ciphertext, so it is unreadable without the key.

Section C: Definitions

plaintext, key, ciphertext — A full-mark answer uses the key terms correctly and gives the steps in order: plaintext is encrypted with a key into ciphertext. Encryption does not stop interception.

Section D: Fill in the Blanks

ciphertext ← ENCRYPT(plaintext, key)

ciphertext ← ENCRYPT(plaintext, key)
plaintext ← DECRYPT(ciphertext, key)

ciphertext ← ENCRYPT(plaintext, publicKey)

ciphertext ← ENCRYPT(plaintext, publicKey)
plaintext ← DECRYPT(ciphertext, privateKey)

Encryption does not stop interception
but ciphertext cannot be read without the key

Section E: Spot the Error

D — Symmetric encryption uses ONE shared key for both encrypting and decrypting. The line should say the same key decrypts it.

D — With asymmetric encryption, data encrypted with the public key can only be decrypted with the matching private key, not the public key.

C — Encryption does not stop data being intercepted. It makes the intercepted ciphertext unreadable without the key.

C — The sender must encrypt with the recipient's public key. Encrypting with a private key is a common mistake and would not keep the message secret.

C — The shared key must be sent to the other person, and it could be intercepted. So sharing it is risky, not always safe.