CardGuard:

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CardGuard Towards software-based signature
detection for intrusion prevention on the network
card Herbert Bos and Kaiming Huang presented by
Willem de Bruijn
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IDS is insufficient

• intrusion prevention is preferable over detection
• active guarding
• nullifies evasion insertion attemps
• but, prevention problematic at traditional
  firewalls
• performance issues
• lack of knowledge
• internal nodes expected safe
• rigid, leading to circumvention

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Move IPS to the edge
CardGuard implements
full payload scanning ,at line-rate
using a software based solution on the network
card
to create a (crude) cost-effective local IPS
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IntroductionArchitectureImplementationResults
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distributed firewalling

• signature detection is easier
• at the network edge
• can overwhelm CPU
• 69Mbps max on 1.8 Ghz P4
• a solution is to offload to the NIC
• unobtrusive difficult to subverge

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Network Processors

• Programmable NICs that combine
• cheap software with fast hardware
• they contain
• stream processors
• asynchronous memory
• hardware assist (e.g., CAM)

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Efficient Pattern Matching

• snort ruleset
• gt28.000 pattern-based rules
• requires parallel processing

Aho Corasick pattern-matching algorithm single-pa
ss complexity independent of patterns
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Aho Corasick Example

• a deterministic finite automaton (DFA)
• for the Slammer worm
• identifies 5 different patterns

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IntroductionArchitectureImplementationResults
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IXP1200

• PCI daughterboard
• or stand-alone box
• two 1Gbps ports
• 6 stream µEngines
• 4 HW threads/engine
• 1 StrongARM CPU _at_ 200Mhz
• IXP 2XXX

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software mapping

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Flow handling

• TCP reconstruction light
• basic flow-accounting
• datastream sanitisation
• Out-of-order handling
• put on hold, or
• two-pass scan

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efficient memory use
memory access is the bottleneck
Registers, 512B, 1 cycle shared
Istore, 1KB, 1 cycle
Scratch, 16KB, 12..14 cycles
SRAM 8 MB , 16..20 cycles
SDRAM 256 MB , 30...40 cycles
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IntroductionArchitectureImplementationResults
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benchmarks
processing costs scale linearly with datarate,
not packetrate
Full TCP scan sustainable at 100Mbit
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conclusions

• intrusion prevention is feasible at the network
  edge
• NP-based solutions are cheap and unobtrusive
• caveat
• CardGuard is only a crude prototype
• lacks a sophisticated management plane