Ciphertext

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Quick Questions

Shade in the A or B circle for each question.

1. Which term describes the scrambled, unreadable data produced when plaintext is encrypted?

A Plaintext

B Ciphertext

2. Which form of the data is sent across the network when encryption is used?

A Ciphertext

B Plaintext

3. An interceptor captures data that was encrypted. Without the key, what does it look like?

A Meaningless scrambled characters

B The original readable message

4. Which of these is an example of ciphertext?

A Xjqqt Btwqi

B Hello World

5. Which statement is correct?

A Encryption turns ciphertext into plaintext

B Encryption turns plaintext into ciphertext

Match the Pairs

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

Left column		Right column
1ciphertext		APlaintext is turned into ciphertext using an encryption key
2ciphertext = encrypt(plaintext, key)		BHELLO is readable plaintext, not ciphertext. Ciphertext should look scrambled, such as KHOOR after encryption.
3Ciphertext is what is sent across the network, so an interceptor only sees scrambled data		CHELLO -> KHOOR
4Plaintext and ciphertext side by side: readable message versus scrambled output		Dsend(network, ciphertext)
5send(network, plaintext)		EThe scrambled, unreadable data produced when plaintext is encrypted
6ciphertext = "HELLO"		FThe readable plaintext is sent instead of the ciphertext, so an interceptor could read it. The encrypted ciphertext should be sent.

Definitions

ciphertext

Fill in the Blanks

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

ciphertext ← _______(plaintext, key)

plaintext ← DECRYPT(__________, key)

SEND(__________, receiver)

ciphertext ← ENCRYPT(plaintext, ___)

IF key = correctKey ____ plaintext ← DECRYPT(ciphertext, key) ENDIF

Spot the Error

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

Question 1

A plain ← "HELLO"

B cipher ← plain

C SEND cipher

Question 2

A cipher ← "PAY NOW"

B key ← 5

C cipher ← encrypt(plain, key)

D SEND cipher

Question 3

A plain ← "GO HOME"

B key ← 1

C cipher ← encrypt(plain, key)

D SEND plain

Question 4

A plain = "CAT"

B cipher = "FDW"

C print("Plain:", cipher)

D print("Cipher:", cipher)

Question 5

A plain = "CAT"

B key = 3

C cipher = encrypt(plain, key)

D print("Cipher:" cipher)

Answer Key

Ciphertext

Section A: Quick Questions

B — Ciphertext

A — Ciphertext

A — Meaningless scrambled characters

A — Xjqqt Btwqi

B — Encryption turns plaintext into ciphertext

Section B: Match the Pairs

ciphertext → The scrambled, unreadable data produced when plaintext is encrypted

ciphertext = encrypt(plaintext, key) → Plaintext is turned into ciphertext using an encryption key

Ciphertext is what is sent across the network, so an interceptor only sees scrambled data → send(network, ciphertext)

Plaintext and ciphertext side by side: readable message versus scrambled output → HELLO -> KHOOR

send(network, plaintext) → The readable plaintext is sent instead of the ciphertext, so an interceptor could read it. The encrypted ciphertext should be sent.

ciphertext = "HELLO" → HELLO is readable plaintext, not ciphertext. Ciphertext should look scrambled, such as KHOOR after encryption.

Section C: Definitions

ciphertext — The scrambled, unreadable data made when plaintext is encrypted. It is what gets sent across a network and looks meaningless without the key.

Section D: Fill in the Blanks

ciphertext ← ENCRYPT(plaintext, key)

plaintext ← DECRYPT(ciphertext, key)

SEND(ciphertext, receiver)

ciphertext ← ENCRYPT(plaintext, key)

IF key = correctKey THEN
   plaintext ← DECRYPT(ciphertext, key)
ENDIF

Section E: Spot the Error

B — Ciphertext is made by encrypting plaintext with a key. Copying plain into cipher leaves the message readable. It should be cipher ← encrypt(plain, 3).

A — The original readable message is plaintext, so it should be stored in plain. As written, plain is never set, so encrypt(plain, key) has nothing to encrypt. It should be plain ← "PAY NOW".

D — The ciphertext is what must be sent across the network. Sending plain would let an interceptor read the message. It should be SEND cipher.

C — The label says Plain but the line prints the ciphertext, so the side-by-side comparison is wrong. It should print plain: print("Plain:", plain).

D — There is a comma missing between the two items in print(). It should be print("Cipher:", cipher).