Information Security: Principles and Practices 2nd Edition by Jim Breithaupt, Mark S. Merkow

Exercise 15

Why does a digital signature contain a message digest?

A. to detect any alteration of the message

B. to indicate the encryption algorithm

C. to confirm the identity of the sender

D. to enable transmission in a digital format

Step 1 of 2

Digital signature

Digital signature is a method that is used to check the authenticity of the message. It ensures the recipient that the message has been send from the intended user only. It also makes use of message digest that ensures the integrity of the data.

The message digests are computed using the SHA-1 algorithm which is then encrypted using the private key. This creates a digitally signed message ready to be sent over the network. At the receiver’s end, a message digest is again created which is matched against the received message digest. If the two are same then, there is no alteration in the message.

Since, message digest is used to detect any alteration in the message.

Hence, the correct option is A. to detect any alteration of the message.