Cryptography A Levels

An ​ (a)   is a another name for a hacker that maliciously reads data sent over a ​ (b)   network.

• eavesdropper
• public
• phisher
• private
• transmitted
• feline

​ (a)   is where only the intended recipient should be able to read or decipher the data.

​ (b)   is the need to identify who sent the data and verify that the source is legitimate.

​ (c)   is that data should reach its destination without any changes.

​ (d)   is that neither the sender nor the recipient should be able to deny that they were part of the data transmission which just took place.

• Confidentiality
• Authenticity
• Integrity
• Non-repudiation

Which is more secure, block cipher or stream cipher?

• block cipher

• stream cipher

Why is a block cipher more secure than a stream cipher?

Answer explanation

A block cipher is more secure than a stream cipher because it is more difficult to break. A stream cipher encrypts data in a continuous fashion, which makes it easier to decrypt. However, a block cipher encrypts data into blocks, which makes it more difficult to decrypt.

With block cipher, each plaintext block is XORed with the previous ciphertext block and then encrypted – this is known as block chaining. This prevents identical blocks of plaintext producing the same ciphertext each time they are encrypted

Which is the key distribution problem most an issue for?

• symmetric encryption

• asymmetric encryption

• digital certificate

• digital signature

Answer explanation

One issue with symmetric encryption is that both sender and recipient need to use the same secret key. This is a security risk here, since the sender has to supply the key to the recipient. This key could be intercepted. This is referred to as the key distribution problem.

Quantum cryptography uses the physical properties of ______ to exchange keys.

Answer explanation

Quantum cryptography uses the physical properties of photons to exchange keys.

What does QKD mean?

Quantum key distribution uses two ​ (a)   . One is ​ (b)   for light waves with a up and down wavelength and the other is ​ (c)   .

• bases
• horizontal-vertical
• diagonal

When a photon with a horizontal wave goes through a filter with a H-V polarization, what is the new wave of the photon?

• horizontal

• vertical

• +45°

• -45°

• random

When a photon with a horizontal wave goes through a filter with a diagonal polarization, what is the new wave of the photon?

• horizontal

• vertical

• +45°

• -45°

• random