In the creation of a digital signature, what is typically computed from the message before signing?

In the creation of a digital signature, what is typically computed from the message before signing?

• A. Encrypting the message using a symmetric key
• B. Verifying the recipient's public key
• C. Computing a hash of the message and signing with a private key
• D. Compressing the message to reduce size

Answer: (C)

In a digital signature, you first create a fixed-size digest of the message by applying a hash function. The signer then encrypts that digest (the hash) with their private key. The result is the digital signature, which can be sent along with the message. Anyone with the signer’s public key can verify the signature by hashing the received message again and checking that the signature corresponds to that hash. This process ensures integrity (any change to the message changes the hash and breaks verification) and authenticity/non-repudiation (the signature proves it came from the holder of the private key). Signing the entire message directly would be impractical for large data, which is why the hash is used. Encrypting the message with a symmetric key would provide confidentiality, not a verifiable, non-reputable signature. Verifying a recipient’s public key relates to key management, not the signing operation itself. Compressing the message is unrelated to the actual signing step and serves a different purpose.

In a digital signature, you first create a fixed-size digest of the message by applying a hash function. The signer then encrypts that digest (the hash) with their private key. The result is the digital signature, which can be sent along with the message. Anyone with the signer’s public key can verify the signature by hashing the received message again and checking that the signature corresponds to that hash. This process ensures integrity (any change to the message changes the hash and breaks verification) and authenticity/non-repudiation (the signature proves it came from the holder of the private key). Signing the entire message directly would be impractical for large data, which is why the hash is used.

Encrypting the message with a symmetric key would provide confidentiality, not a verifiable, non-reputable signature. Verifying a recipient’s public key relates to key management, not the signing operation itself. Compressing the message is unrelated to the actual signing step and serves a different purpose.