Message Encryption if public-key encryption is used encryption provides no confidence of sender, if the sender uses private key to encrypt the message since anyone potentially knows public-key however if sender signs message using their private-key then encrypts with recipients public key have both confidentiality and authentication again need to recognize corrupted messages but at cost of two public-key uses on message 13 復大软件学院13 Message Encryption • if public-key encryption is used: – encryption provides no confidence of sender, if the sender uses private key to encrypt the message – since anyone potentially knows public-key • however if • sender signs message using their private-key • then encrypts with recipients public key • have both confidentiality and authentication – again need to recognize corrupted messages – but at cost of two public-key uses on message