ITPEC FE Morning April 2020 Question 40
ITPEC FE Morning April 2020 — Question 40 of 80
Public Key Encryption — decryption with paired private key — only the holder of the matching private key can decrypt.
A encrypts an email using B's public key and sends it to both B and C.
- •Asymmetric encryption rule: data encrypted with a public key can only be decrypted by the corresponding private key
- •B's public key → only B's private key can decrypt
- •C has their own private key, but it does not match B's public key
Answer: (d) — Only B can decrypt using B's own private key.
Why not others:
- (a) B's public key encrypts, it cannot decrypt — that reverses how asymmetric crypto works
- (b) C's private key only decrypts data encrypted with C's public key, not B's
- (c) A's public key was never used for encryption in this scenario
Key rule: In asymmetric encryption, public key encrypts → only the paired private key decrypts. Sending to multiple recipients with one key does not give all recipients decryption ability.
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