Information Technology Reference
In-Depth Information
Public-key encryption uses a
private
key and a
public
key. The private key is known only to the
source system. The public key is given to the receiver or any system that wants to communicate
securely with it. To decode an encrypted message, a system must use the public key, which is
provided by the originating system, and its own private key. All systems keep their private key
secret but share the public key with everyone who might want to communicate with them.
Cisco Encryption Technology (CET)
Encryption can occur in one of three places in the Open System Interconnection (OSI) layered
model:
•
Physical/data-link (1-2)
•
Network/transport (3-4)
•
Application layers (5-7)
Physical encryption occurs in specialized hardware to encrypt data in links. Application layer
encryption occurs between end hosts. Network layer encryption is routable. Cisco implements
network layer encryption with its CET.
CET uses the following technologies:
•
Digital Signature Standard (DSS)
—A public/private key system to verify the identity of
another party and also to prove a user's own identity when communicating through
electronic means.
•
Diffie-Hellman
—For key exchange, but it does not exchange the keys.
•
Digital Encryption Standard (DES)
—Encrypts and decrypts data.
DES
DES is a U.S. Government standard that is widely used for encryption. DES uses a 56-bit key
to scramble and unscramble messages. A 40-bit bit version exists for exported DES. The latest
DES standard uses a 3
56 bit key (168 bit-key called Triple DES), where the input is encrypted
three times. When you use it for communication, both sender and receiver must know the same
secret key, which can encrypt and decrypt the message, or generate and verify a message
authentication code.
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Desktop Protocols
This section covers desktop protocols that are still included in the new CCIE Routing and
Switching (R&S) written exam blueprint. Cisco removed AppleTalk and DECnet from the
blueprint. This section discusses Novell IPX addressing and protocols and Windows NT
protocols.
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