Encryption Question:

Cara is dating Dan and Evan. Cara wants to send a message to break up with Dan. Dan has been receiving lots of spam email lately, so Cara wants to make sure that Dan knows the message is from her. Using public key cryptography, how does Cara send a digitally signed "I'm breaking up with you" message to Dan? Assume that m = "I'm breaking up with you".

a. KD+ (m)

b. KC- (m)

c. KC+ (m)

d. KD- (m)