Project ForgeConsider that B wants to send a message m that is digitally signed to A. Let the pair of private and public keys for A and B be denoted by Kx⁻ and Kx⁺ for x=A,B respectively. Let Kx(m) represent the operation of encrypting m with key Kx and H(m) represent the message digest. Which one of the following indicates the CORRECT way of sending the message m along with the digital signature to A?
- A{m, KB⁺(H(m))}
- {m, KB⁻(H(m))}
- C{m, KA⁻(H(m))}
- D{m, KA⁺(m)}
Explanation
A digital signature is created by the SENDER (B) encrypting the message digest with B's OWN PRIVATE key (KB⁻) — this lets anyone verify authenticity using B's public key, while only B could have produced it. So the correct pair is {m, KB⁻(H(m))}.
Source: GATE CS 2016 (Session 1 / Set A) (2016)
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