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Botz-4-Sale: Surviving Organized DDoS Attacks That Mimic Flash Crowds. Srikanth Kandula, Dina Katabi, Matthias Jacob, and Arthur Berger Awarded Best Student Paper! (NSDI-2005) Defense by Manan Sanghi. Flash Crowd. DDOS. Botz-4-Sale. request. Botz-4-Sale. Reverse Turing test. Botz-4-Sale.
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Botz-4-Sale: Surviving Organized DDoS Attacks That Mimic Flash Crowds Srikanth Kandula, Dina Katabi, Matthias Jacob, and Arthur Berger Awarded Best Student Paper! (NSDI-2005) Defense by Manan Sanghi
Botz-4-Sale request
Botz-4-Sale Reverse Turing test
Botz-4-Sale Solution
Botz-4-Sale Welcome! • HTTP cookie • Allows at most 8 simultaneous connections • Valid for 30 minutes
Botz-4-Sale request
Botz-4-Sale Reverse Turing test
Botz-4-Sale request
Botz-4-Sale System is Busy, either solve puzzle or try later
Botz-4-Sale request
Botz-4-Sale Reverse Turing test
Botz-4-Sale request
Botz-4-Sale System is Busy, either solve puzzle or try later
Botz-4-Sale Request Request Request …
Kill-Bots Overview Graphical Puzzles served during Stage 1
Time out (5 minutes) unauthenticated users Example Normal Load 40% K1=70% K2=50%
Two stages in Suspected Attack Mode • Stage 1: CAPTCHA based Authentication • No state maintenance before authentication • HTTP cookie • Cryptographic support • Stage 2: Authenticating users who do not answer CAPTCHA • No more reverse Turing tests • Bloom filters to filter out over-zealous zombies
Resource Allocation and Admission Control • Tradeoff • Authenticate new clients • Serve already authenticated clients
Adaptive Admission Control • Cute Queuing Theory type analysis
Security Analysis • Socially-engineered Attacks • Copy Attacks • Including IP address in one-way hash does not deal well with proxies and mobile users • Replay Attacks • Time information in the cookie hash • DoS attacks on the authentication mechanism • No connection state for unauthenticated clients • In-kernel HTTP header processing • HTTP headers not parsed • Pattern match arguments to GET and Cookie fields • Cost : less than 8 s
On Admission Control • Authentication is not sufficient • Good performance requires admission control
Threat Model • Bandwidth floods, DNS entries, routing entries not considered • Attacker cannot sniff legitimate users’ packets • Attacker cannot access server’s local network • Zombies are not as smart as humans • Attacker does not have a large number of humans aiding his evil plans