Private and Public Key Systems:

Symmetric encryption/decryption is much
faster than asymmetric encryption/
decryption:
RSA: kilobits/second
DES: megabits/second
⇓
DES is about 100 times faster than RSA

Authentication Application::
KERBEROS

Users wish to access services on servers.
• Three threats exist:
– User pretend to be another user.
– User alter the network address of a computer.
– User eavesdrop on exchanges and use a replay
attack.

Provides a centralized authentication server
(AS) to authenticate users to servers and
servers to users.
• Relies on conventional encryption.
– Makes no use of public-key encryption.
• Two versions: version 4 and 5.
• Version 4 makes use of DES.

Electronic Mail Security:: Pretty
Good Privacy (PGP)

PGP provides a confidentiality and
authentication service that can be used for
electronic mail and file storage applications.
• Why popular?
– It is availiable free on a variety of platforms.
– Based on well known algorithms.
– Wide range of applicability