Signing a message digest means encrypting it with the sender's public key.

• A. True
• B. False
• C. Not applicable
• D. It depends

Answer: (B)

Signing a message digest relies on using the sender’s private key to create the signature, not the public key. The process is: hash the message to get a digest, then encrypt that digest with the sender’s private key to form a digital signature. Anyone can verify it by decrypting the signature with the sender’s public key and comparing the result to a fresh hash of the message. This setup ensures authenticity and non-repudiation, because only the private key holder could have created that signature, while the public key can be shared openly for verification. If the public key were used to sign, anyone who has the private key could not be prevented from forging signatures, and verification would not reliably prove the signer’s identity. Therefore, the statement is false.