CCNA网路基础 part3 basic security.pptVIP

網路訓練課程 - Part IIIBasic Security Concept Encryption: What Is It? Encryption and Decryption Classical Cryptography vs. Public Key Encryption Alternatives Link Encryption Encrypts all traffic on a link, including network-layer headers Specific to media/interface type, but protocol independent Topology dependent Traffic is encrypted/decrypted on link-by-link basis All alternative paths must be encrypted/decrypted Application Encryption Encryption Options Network Encryption Encrypts traffic on a flow-by-flow basis Media/interface independent Does not need to supported by intermediate network devices Public Key Encryption Example Alice wants to send Bob encrypted data Alice gets Bob public key Alice encrypts the data with Bob public key Alice sends the encrypted data to Bob Bob decrypts the data with his private key Diffie-HellmanPublic Key Exchange Man-in-the-Middle Attack Signature Verification Keyed Hashingfor Authentication Secret key and message are hashed together Recomputation of digest verifies that message originated with peer and that message was not altered in transit Problem Is the Secret Key! Encryption and decryption use same key Peers have to share the same key Key length matters ^$!@#l:{Q Secret Encryption Decryption DES DES Secret Encryption Clear-Text Clear-Text Cipher Text Bob Is a Fink 8vyaleh31d ktu.dtrw8743 $Fie*nP093h Bob Is a Fink Decryption Symmetric Algorithm Asymmetric Algorithm Dual-PurposeKey Locking Key Unlocking Key Network-Layer Encryption Application-Layer Encryption Link-LayerEncryption Link-LayerEncryption Application Layers (5?) Transport/Network Layers (3?) Physical/Link Layers (1?) Encrypts traffic to/from that application Specific to application, but network independent Application dependent All users must have same application Application Layer Needs to Be on Every Host Data Link Layer Needs to Be on Every Link HR Server E-Mail Server A to HR Server?ncrypted All Other Traffic?lear Message Alice Bob Encrypte