With a Caesar shift of 3 forward, what does C become?

• E
• G
• F

What makes an encryption scheme symmetric?

• It uses the same secret key to encrypt and decrypt
• It uses a public key to encrypt and a private key to decrypt
• It uses the message's length instead of a secret key

Keeping the algorithm secret is a substitute for using a sound encryption scheme.

Which claim is not supplied by confidentiality-only symmetric encryption?

• Correct decryption uses the shared secret key
• The message was sent by a particular person
• Protected contents resist the defined eavesdropper

A network observer cannot decrypt a packet but can see its endpoints and timing. What can they still record?

• The packet's endpoints and when it was sent
• The packet's plaintext and the sender's secret key
• The receiver's password and the sender's plaintext

Two plaintexts are XORed with the same keystream S. What does XORing their ciphertexts reveal?

• The keystream S without any plaintext knowledge
• The length of S but no relation between plaintexts
• The XOR of the two plaintexts because S cancels

A sender encrypts a new shared secret to a public key received without checking whose key it is. What risk remains?

• Ciphertext length alone lets every observer compute the secret
• An attacker could substitute their own key and decrypt it
• The recipient must publish a private key before receiving data

Vigenere uses A for shift 0 and B for shift 1. Encrypt CC with key AB. What is the ciphertext?

• CD
• DD
• CC