© 2007 Cisco Systems, Inc. All rights reserved. ICND1 v1.0—1-1

Cisco Security

© 2007 Cisco Systems, Inc. All rights reserved. ICND1 v1.0—1-2

An Example

=> How to transport the letter safely ?

=> Worry somebody intercept the letter ?

=> Worry somebody falsify the letter ?

=> Worry writter or transporter negative the letter ?

© 2007 Cisco Systems, Inc. All rights reserved. ICND1 v1.0—1-3

Security Meaning

=> Ensure the source

=> Ensure the message could not be falsify or intercept

while transportion

=> Ensure the message could not be cracked

=> No negation

© 2007 Cisco Systems, Inc. All rights reserved. ICND1 v1.0—1-4

Basics of Encryption

There are two types of encryption keys:

=> Symmetric

=> Asymmetric

© 2007 Cisco Systems, Inc. All rights reserved. ICND1 v1.0—1-5

Symmetric

With symmetric key encryption, each peer uses the same

key to encrypt and decrypt the data.

© 2007 Cisco Systems, Inc. All rights reserved. ICND1 v1.0—1-6

Symmetric Encryption

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Maybe Perfect

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An Obvious Problerm

=> How to send the "key" ?

=> QQ ? MSN ? E-mail ? Telephone ?

=> Bike ? Bus ? Train ? Airplane ?

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Asymmetric

With asymmetric key encryption, the local end uses one

key to encrypt,and the remote end uses another key to

decrypt the traffic.

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Asymmetric Encryption

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Maybe Perfect

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An Obvious Problem

=> Cracker will exchange the letter . How to solve this

problerm ?

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A perfect Encryption

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A Perfect Decryption

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