Smart Phone and Next Generation Mobile Computing

348 Smart Phone and Next-Generation Mobile Computing

DES; for example, a message can be encrypted using the DES CBC

(Cipher Block Chaining) mode. The ciphertext can then be used as

MAC. Furthermore, to prevent tampering of the message digest itself,

the sender can encrypt the message digest using its own private key

so the recipient, with the sender’s public key at hand, can be assured

that this message has come from the sender. This scheme is referred

to as digital signature and will be discussed in the next subsection.

As a last note, an attacker may launch a message reply attack by

simply resending a number of legitimate messages previously cap-

tured. The recipient may be fooled by such legitimate messages.

To counteract these attacks, the sender ...