In checking the digital signature, the verifier ________.

• A. Decrypts the digital signature it received with the supplicant's public key to get the message digest
• B. Hashes the plaintext message with the same algorithm used by the sender to get the message digest
• C. Both A and B
• D. Neither A nor B

Answer: (B)

Digital signatures bind a message to the signer by signing a hash of the message with the signer’s private key. To verify, the recipient uses the signer’s public key to recover the digest from the signature and independently hashes the received message with the same algorithm to produce a second digest. If these two digests match, the signature is valid. The key action for checking the signature is hashing the plaintext to produce the message digest that will be compared to the recovered digest. This hashing provides the basis for the integrity check, confirming the message hasn’t been altered and that the signature was created with the signer’s private key.