Intrusion Detection System

The Network Intrusion Detection System processes PCAP Files to detect attack using a signature database provided in TOML format. Each signatures in the file are regular expression over byte strings and are matched against IP datagram payloads and TCP streams.

This intrusion detection system has the following capabilities:

• Bounded memory use during execution using buffer trimming to prevent DoS attacks
• IPv4 and TCP checksum verification failing to which packets are dropped silently
• Custom TCP stream reassembly implementing a first-received policy for overlapping segments
• Do not track TCP sessions where initial TCP handshake was not observed

Logging Detection

Detections are printed to stdout as individual JSON objects, one per line.

The format of a single detection is:

{
    "tv_sec": 160074820,           # Packet timestamp in seconds
    "tv_usec": 0,                   # Packet timestamp microseconds field
    "source": {
        "ipv4_address": "10.0.0.1", # Source IPv4 address
        "tcp_port": 1234           # Source TCP port, or null if N/A
    },
    "target": {
        "ipv4_address": "10.0.0.2", # Target IPv4 address
        "tcp_port": 34567            # Target TCP port, or null if N/A
    },
    "attack": 0                     # Signature index in database (0-indexed)
}

Build and Run

Install Docker.

Once docker is installed, clone the repository, and follow the steps below.

1. Build the docker image - docker build --pull --rm -f "nids/Dockerfile" -t <image_name>:latest "nids"
2. Run the docker image - docker run -it -m 256m -v $(pwd):/data <image_name}> /data/<database_filename> /data/<pcap_filename>

• -v $(pwd):/data : mounts the current working directory to the container as /data. $(pwd) can be replaced by the directory path where database files and pcap files are stored.
• /data/<database_filename>, /data/<pcap_filename> : Path for signature db file and pcap file may vary according to the directory structure maintained.
• -m : sets the memory bound for the docker container