Transport Layer - Freie Universität Berlin
Transport Layer - Freie Universität Berlin
Transport Layer - Freie Universität Berlin
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TCP and Security: SYN-Flood<br />
● Countermeasure: SYN cookies<br />
● Server does not creates a half-open<br />
connection<br />
● Server computes an initial sequence<br />
number y based on a hash function<br />
● This is the cookie<br />
● When client returns with ACK the<br />
server recomputes the hash<br />
function and checks it<br />
● For legitimate connection the check<br />
will be successful<br />
Client<br />
Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 8: <strong>Transport</strong> <strong>Layer</strong><br />
Server<br />
y=h()<br />
Check y<br />
8.120
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