CS/CoE 535 : Snort Lite - Fall 2003 1

Snort Lite

Members•Michael Attig (mea1@arl)

–Hardware Design / System Architecture•Qian Wan (qw2@arl)

–Software Design

Webpage http://www.arl.wustl.edu/arl/projects/fpx/snort_lite/

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Motivation

• Built up ability to do packet inspection• Would like to add some form of packet-

classification • Combining these 2 features is a first step

toward implementing Snort in hardware– Ideally reach line rates– Inspect all packets– Turn Snort active

• Header Processing + Payload Processing

CS/CoE 535 : Snort Lite - Fall 2003 3

Assumptions

• Time constraints force several assumptions– Support Signature lengths from 10 to 32

characters long (80 to 256 bits)– 1 content-rule can be associated with only 1

header rule– Must have content and header rule

• Content + Header = Rule– No content Wildcards (no regular expressions)– Wildcards are allowed in Header Fields– Recognize IP, TCP, UDP protocols

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Hardware Overview

Packet Data

SID

Matching Rule

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Major Components Functionality

• Options Processing– Payload Processing via Multiple Bloom Filters

• 8 Hash Functions per BF• False Positive Probability 0.0039

– SDRAM Hash Table Implementation (Quadratic Probing)

• Expected Number of Lookups = ?

• Header Processing– SRAM table lookup– Header Fields Comparator

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Chip Utilization

• Number of 4-input LUTs – 63%• Number of Occupied Slices – 88%• Number of Block RAMs – 123 of 160 – 76%• Speed – 34.7 MHz

– (this number doesn’t reflect current design)!

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Control Opcodes

• x70 – Add String to Hash Table• x72 – Remove String from Hash Table• x74 – Set Bits in a Bloom Filter• x76 – Add Header Table Entry• x78 – Remove Header Table Entry• x80 – Change Alert Message Destination• x82 – Read Header Table Entry• x84 – Read Statistics• x86 – Test Functionality / Pass Through

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Example Rule

• alert tcp 128.252.153.51/16 any 192.168.200.10 80 (content: “Look at my Sample content!”; sid:750;)

• Generic– action proto src_ip src_port dest_ip dest_port

(content: sid:)

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Java Rule Parser

• Reads in a Rule File• Creates the payload for 3 control

packets to program Circuit– x70 – add signature to analyzer– x74 – set bits in appropriate

Bloom Filter– x76 – Add Header Entry

• Tells you if a rule doesn’t match assumptions

• Ignores other fields – Just extracts content and sid

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Data Flow Overview

Add rules from web interface

Save rules into database

Construct rules to plain text

Parse rules into payloadsRecord matches in database

Output statistics to web page

Construct payloads to UDP

Update Bloom Counter

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Updated Table definitions in DB snortlight

TABLES

BLOOMFILTER --------------------- Id INT ; // identity(1, 1) BlockRAM1 INT ; // the ID of BlockRAM 1 BlockRAM2 INT ; // the ID of BlockRAM 2 BlockRAM3 INT ; // the ID of BlockRAM 3 BlockRAM4 INT ; // the ID of BlockRAM 4 BlockRAM5 INT ; // the ID of BlockRAM 5

RULES ---------- Id INT ; // identity(1, 1) BloomId INT ; // FK of BLOOMFILTER Content VARCHAR(100) ; // NOT NULL SourceIP VARCHAR(30) ; DestIP VARCHAR(30) ; SourcePort VARCHAR(20) ; DestPort VARCHAR(20) ; NoCase ENUM(“FALSE”, “TRUE”) ; // 0 false InHardware ENUM(“FALSE”, “TRUE”) ; // 0 false Action CHAR(5) ; // actions to take Protocol CHAR(5) ; // type of protocol InsertTime DATE; DeleteTime DATE; KeepLog ENUM(“FALSE”, “TRUE”) ; // 0 false

BLOOMCNTR ------------------

BloomId INT ; BlockRAMId VARCHAR(10) ; BitPosition INT ; Counter INT ;

RULEMATCH ------------------

PacketID INT ; RuleID INT ; // FK of RULES EventDT DATE;

MATCHSTATIS // use 0 for false match -------------------- RuleID INT ; BloomID INT ; StartDT DATE; EndDT DATE; counter INT ;

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Graphical Processes Illustrationalert tcp 127.0.0.0/9 any -> 128.252.153.0/24 801 (content: "CSE 535 is fun but harder!"; sid:68;)

•traffic first•match result

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Web Interface– Add a Rule

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Web Interface– Result of Adding a Rule

alert tcp 127.0.0.0/9 any -> 128.252.153.0/24 801 (content: "CSE 535 is fun but harder!"; sid:68;)

•-Temprulei.txt-

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Web Interface– Display Rules

Actual Snort rules contents shown above.

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Delete one rule just entered

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Result page after one rule deleted

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Append rule matches

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Rule Matches Statistics

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Future Work

• Redesign – too many assumptions• Allow Header-only and content-only rules• Implement more content-based features

– TCP flags– IP options– More header fields– Multiple Signatures per content rule

• Snort has many over-lapping rules

• Software to dynamically recreate VHDL to change Number of PBFs per LBF based on number of strings for a particular length– Statistical Modeling would help determine this