Plaintext

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Quick Questions

Shade in the A or B circle for each question.

1. Which statement describes plaintext?

A Scrambled data that cannot be read without a key

B The original, readable data before it is encrypted

2. Plaintext can only ever be typed text, such as an email.

A False - it can be a file, image or message

B True - only text counts as plaintext

3. A student's photo is sent over a network. Before it is encrypted, the photo is:

A Plaintext

B Ciphertext

4. If a hacker intercepts plaintext, what can they do?

A Read and understand it straight away

B Nothing, because it is always scrambled

5. What is the result of decrypting ciphertext with the correct key?

A A new encryption key

B Plaintext

Match the Pairs

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

Left column		Right column
1plaintext		APlaintext is readable by anyone who gets it, so an interceptor can read it. Only ciphertext is unreadable.
2decrypt(ciphertext, key) = plaintext		BDecrypting with the correct key turns unreadable data back into plaintext
3Plaintext is not only text: an image or file that is readable before encryption is also plaintext		Cciphertext = encrypt(plaintext, key)
4Plaintext is the input to encryption, and encrypting it produces ciphertext		DThis shows plaintext as the output of encryption. Encryption produces ciphertext, not plaintext.
5plaintext = encrypt(message, key)		Eplaintext = photo.jpg
6An interceptor cannot read plaintext		FThe original, readable data before it is encrypted

Definitions

plaintext

Fill in the Blanks

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

_________ ← "photo.png"

ciphertext ← encrypt(_________, key)

plaintext ← _______(ciphertext, key)

ciphertext ← _______(plaintext, key)

plaintext ← decrypt(ciphertext, key) OUTPUT _________

Spot the Error

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

Question 1

A plain ← "Meet at noon"

B plain ← ENCRYPT(plain, 3)

C OUTPUT cipher

Question 2

A cipher ← "Phhw dw qrrq"

B key ← 3

C plain ← ENCRYPT(cipher, key)

D OUTPUT plain

Question 3

A image ← "photo.png"

B key ← 7

C cipher ← DECRYPT(image, key)

D OUTPUT cipher

Question 4

A plain ← "Pay Sam $20"

B cipher ← ENCRYPT(plain, 5)

C OUTPUT "Seen: " + cipher

D OUTPUT "Readable: " + cipher

Question 5

A message ← "See you at 8"

B cipher ← message

C OUTPUT plain

Answer Key

Plaintext

Section A: Quick Questions

B — The original, readable data before it is encrypted

A — False - it can be a file, image or message

A — Plaintext

A — Read and understand it straight away

B — Plaintext

Section B: Match the Pairs

plaintext → The original, readable data before it is encrypted

decrypt(ciphertext, key) = plaintext → Decrypting with the correct key turns unreadable data back into plaintext

Plaintext is not only text: an image or file that is readable before encryption is also plaintext → plaintext = photo.jpg

Plaintext is the input to encryption, and encrypting it produces ciphertext → ciphertext = encrypt(plaintext, key)

plaintext = encrypt(message, key) → This shows plaintext as the output of encryption. Encryption produces ciphertext, not plaintext.

An interceptor cannot read plaintext → Plaintext is readable by anyone who gets it, so an interceptor can read it. Only ciphertext is unreadable.

Section C: Definitions

plaintext — The original, readable data (text, file, image or message) before it is encrypted. Decrypting ciphertext with the correct key turns it back into plaintext.

Section D: Fill in the Blanks

plaintext ← "photo.png"

ciphertext ← encrypt(plaintext, key)

plaintext ← decrypt(ciphertext, key)

ciphertext ← encrypt(plaintext, key)

plaintext ← decrypt(ciphertext, key)
OUTPUT plaintext

Section E: Spot the Error

B — The result of encryption is ciphertext, not plaintext. It should be stored in cipher: cipher ← ENCRYPT(plain, 3). The variable plain must keep the original readable data.

C — Plaintext is produced by decrypting ciphertext with the correct key. ENCRYPT would scramble the data again. It should be plain ← DECRYPT(cipher, key).

C — An image is plaintext too, because it is original data before encryption. It must be encrypted, not decrypted: cipher ← ENCRYPT(image, key).

D — Plaintext is the data anyone can read and understand. Ciphertext is unreadable without the key. The readable output should use plain, not cipher.

B — A message that has not been encrypted is plaintext. It has not been scrambled, so it should be stored as plain, not cipher: plain ← message.