A digital signature contains a message digest to:

A.
show if the message has been altered after transmission.

B.
define the encryption algorithm.

C.
confirm the identity of the originator.

D.
enable message transmission in a digital format.

Explanation:
The message digest is calculated and included in a digital signature to prove that the message has not been altered. It should be the same value as a recalculation performed upon receipt. It does not define the algorithm or enable the transmission indigital format and has no effect on the identity of the user; it is there to ensure integrity rather than identity.