Cryptography

Question 1

Plaintext definition:

Answer 1

Information which can be directly read by humans: this can be code, text or textual representations of films or music.

Question 2

Ciphertext definition:

Answer 2

The encrypted version of the plaintext. Cannot be read by (and enterpreted as the plaintext by) humans. Can only be read after decryption with the correct algorithm.

Question 3

Cipher definition:

Answer 3

The algorithm for generating ciphertext from plaintext.

Question 4

Encryption definition:

Answer 4

The process of converting plaintext into ciphertext using a specific cipher.

Question 5

Decryption definition:

Answer 5

The process of converting ciphertext back to plaintext. The correct algorithm must be used, otherwise the resulting plaintext will not be correct.

Question 6

Encryption key definition:

Answer 6

Keys control small variables in a cipher. This means that a single cipher can be used to produce almost limitless different possible output values for the same piece of plaintext.

Question 7

What is the key distribution problem?

Answer 7

The problem with transmitting keys between two computers, because keys could be intercepted and copied.

Question 8

What is symmetric encryption?

Answer 8

Encryption using a single key.

Question 9

What is asymmetric encryption?

Answer 9

Each user has a key for encrypting and decrypting. The plaintext is encrypted with the current user’s private key, then again with the other user’s public key.

Question 10

Private and public keys:

Answer 10

One user’s private key is used to decrypt messages encrypted with another user’s public key.