Alice needs to send a confidential document to her coworker. Bryan. Their company has public key infrastructure set up. Therefore. Alice both encrypts the message and digitally signs it. Alice uses___

Question

Options

• ABryan's public key; Bryan's public key
• BAlice's public key; Alice's public key
• CBryan's private key; Alice's public key
• DBryan's public key; Alice's public key

• A
  2% (1)
• B
  2% (1)
• C
  6% (3)
• D
  90% (47)

Explanation

Option D is correct because in a Public Key Infrastructure (PKI) system, encryption and digital signatures use different key pairs for different purposes: Alice encrypts the message using Bryan's public key so that only Bryan (with his matching private key) can decrypt it, ensuring confidentiality; Bryan then verifies Alice's digital signature using Alice's public key, which confirms the message genuinely came from Alice (since only she has her private key to create that signature).

Why the distractors are wrong:

• A is incorrect because using Bryan's public key to verify a signature makes no sense - signatures are verified with the sender's public key, not the recipient's.
• B is incorrect because encrypting with Alice's own public key would mean only Alice could decrypt it (with her private key), defeating the purpose of sending it to Bryan.
• C is incorrect because Bryan's private key is never shared - it stays secret with Bryan and is used only for decryption, not by Alice for encryption.

Memory tip: Think of it this way - "Lock with the recipient's public key, verify with the sender's public key." Encryption uses the receiver's public key (Bryan receives it → use Bryan's public key), and signature verification uses the sender's public key (Alice sent it → use Alice's public key).

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