ITPEC FE Subject A October 2025 Question 28
ITPEC FE Subject A October 2025 — Question 28 of 60
Digital signature verification — identifying which key verifies a sender's digital signature.
In public key cryptography, a digital signature works as follows:
- The sender (Y) signs the message using Y's private key
- The receiver (X) verifies the signature using Y's public key
If the signature decrypts correctly with Y's public key, it proves the message truly came from Y — because only Y possesses the matching private key.
Why not others:
- (a) X's private key is used for X to decrypt messages sent to X, not to verify Y's signature
- (b) X's public key is used by others to encrypt messages for X, unrelated to verifying Y
- (c) Y's private key is what Y uses to create the signature — it is never shared, so X cannot use it
Key rule: Digital signature = sender signs with their own private key, receiver verifies with sender's public key.
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