Server grants network access if successful wire client

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Unformatted text preview: ice! Password? Bob Trudy Computer Networks 29 Preven7ng Replays (3) •  To prevent replays, include proof of freshness in messages –  Use a 7mestamp, or nonce Freshness OK Alice! Tue 10:03:57: “sell stocks” Alice Message MAC Bob Confiden7ality Authen7city/Integrity Computer Networks 30 15 12/3/13 Takeaway •  Cryptographic designs can give us integrity, authen7city and freshness as well as confiden7ality. •  Real protocol designs combine the proper7es in different ways –  We’ll see some examples –  Note many pivalls in how to combine, as well as in the primi7ves themselves Computer Networks 31 Introduc7on to Computer Networks Wireless Security (§8.6.4) Computer Science & Engineering 16 12/3/13 Goal and Threat Model •  Unlike wired, wireless messages are broadcast to all nearby receivers –  Don’t need physical network access –  Heightens security problems Alice Bob Eve/Trudy Computer Networks 33 Goal and Threat Model (2) •  Two main threats: 1.  Eavesdropping on conversa7ons 2.  Unauthorized access to network •  We’ll consider 802.11 sewng –  Assume external aNacker can send/ receive wireless messages Computer Networks 34 17 12/3/13 802.11 Security •  Provides access control, and message confiden7ality, integrity/authen7city –  Keying based on passwords •  802.11 standard (1999) used WEP –  For “Wired Equivalent Privacy” –  Badly flawed, easily broken •  802.11i standard in 2004 –  WiFi Protected Access or WPA2 –  This is what you should use Computer Networks 35 802.11 Security (2) •  Secu...
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