Implementing Iec 62443 Security Zones

# IEC 62443-3-2 Zone Definition Document
facility: "Petrochemical Refinery - Unit 3"
assessment_date: "2026-02-23"
standard: "IEC 62443-3-2:2020"

zones:
  - zone_id: "Z1-SIS"
    name: "Safety Instrumented Systems"
    purdue_level: 1
    security_level_target: "SL 3"
    criticality: "Safety Critical"
    assets:
      - "Triconex 3008 Safety Controller (SIS-01)"
      - "Triconex 3008 Safety Controller (SIS-02)"
      - "SIS Engineering Workstation"
    security_requirements:
      - "Physically isolated from all other zones (air-gapped)"
      - "Dedicated engineering workstation with removable media controls"
      - "No remote access permitted under any circumstances"
      - "Change management requires dual authorization"
    allowed_conduits: []  # No network conduits - fully air-gapped

  - zone_id: "Z2-BPCS"
    name: "Basic Process Control System"
    purdue_level: "1-2"
    security_level_target: "SL 2"
    criticality: "High"
    assets:
      - "Allen-Bradley ControlLogix PLCs (PLC-01 through PLC-12)"
      - "Rockwell FactoryTalk View HMIs (HMI-01 through HMI-06)"
      - "Engineering Workstation (EWS-01)"
    security_requirements:
      - "Industrial firewall at zone boundary with protocol inspection"
      - "Read-only access from Level 3 for data acquisition"
      - "Write access restricted to engineering workstation subnet"
      - "USB ports disabled on HMIs"
    allowed_conduits: ["C1-BPCS-OPS"]

  - zone_id: "Z3-OPS"
    name: "Site Operations"
    purdue_level: 3
    security_level_target: "SL 2"
    criticality: "Medium"
    assets:
      - "OSIsoft PI Historian (HIST-01)"
      - "OPC UA Server (OPC-01)"
      - "MES Application Server (MES-01)"
      - "Alarm Management Server (ALM-01)"
    security_requirements:
      - "Firewall between operations and control zones"
      - "Firewall between operations and DMZ"
      - "No direct internet access"
      - "Antivirus with OT-approved signatures"
    allowed_conduits: ["C1-BPCS-OPS", "C2-OPS-DMZ"]

  - zone_id: "Z4-DMZ"
    name: "Industrial Demilitarized Zone"
    purdue_level: 3.5
    security_level_target: "SL 2"
    criticality: "Medium"
    assets:
      - "PI-to-PI Interface (DMZ-HIST-01)"
      - "Patch Management Server (DMZ-WSUS-01)"
      - "Remote Access Jump Server (DMZ-JUMP-01)"
      - "Data Diode - Waterfall Security (DMZ-DD-01)"
    security_requirements:
      - "Dual-homed firewalls on both sides"
      - "No direct traffic traversal - all connections terminate in DMZ"
      - "Data diode for unidirectional historian replication"
      - "Jump server with MFA for remote access"
    allowed_conduits: ["C2-OPS-DMZ", "C3-DMZ-ENT"]

  - zone_id: "Z5-ENT"
    name: "Enterprise Network"
    purdue_level: 4
    security_level_target: "SL 1"
    criticality: "Low (from OT perspective)"
    assets:
      - "Corporate systems accessing OT data"
    security_requirements:
      - "Firewall between enterprise and DMZ"
      - "No direct access to any OT zone below DMZ"
    allowed_conduits: ["C3-DMZ-ENT"]

conduits:
  - conduit_id: "C1-BPCS-OPS"
    name: "Control-to-Operations Conduit"
    connects: ["Z2-BPCS", "Z3-OPS"]
    security_level: "SL 2"
    protocols_allowed:
      - protocol: "OPC UA"
        port: 4840
        direction: "Z2 -> Z3 (read only)"
        security_mode: "SignAndEncrypt"
      - protocol: "Modbus/TCP"
        port: 502
        direction: "Z3 -> Z2 (read only, FC 3/4 only)"
        security_mode: "Firewall-enforced function code filtering"
    controls:
      - "Industrial firewall with OT protocol DPI"
      - "Allowlisted source/destination IP pairs"
      - "Function code filtering (block all write operations from L3)"
      - "Connection rate limiting"

  - conduit_id: "C2-OPS-DMZ"
    name: "Operations-to-DMZ Conduit"
    connects: ["Z3-OPS", "Z4-DMZ"]
    security_level: "SL 2"
    protocols_allowed:
      - protocol: "PI-to-PI"
        port: 5450
        direction: "Z3 -> Z4 (unidirectional via data diode)"
      - protocol: "HTTPS"
        port: 443
        direction: "Z4 -> Z3 (patch downloads only)"
    controls:
      - "Data diode for historian replication (Waterfall Security)"
      - "Firewall with application-layer inspection"
      - "Patch server pulls only from approved vendor repositories"

  - conduit_id: "C3-DMZ-ENT"
    name: "DMZ-to-Enterprise Conduit"
    connects: ["Z4-DMZ", "Z5-ENT"]
    security_level: "SL 1"
    protocols_allowed:
      - protocol: "HTTPS"
        port: 443
        direction: "Z5 -> Z4 (historian read, remote access portal)"
      - protocol: "RDP"
        port: 3389
        direction: "Z5 -> Z4 (jump server with MFA)"
    controls:
      - "Next-gen firewall with SSL inspection"
      - "MFA required for all remote access sessions"
      - "Session recording on jump server"

# Cisco ISA-3000 Industrial Firewall Configuration
# Conduit C1: BPCS (Zone 2) <-> Operations (Zone 3)

# Define zone interfaces
interface GigabitEthernet1/1
  nameif zone-bpcs
  security-level 90
  ip address 10.20.1.1 255.255.0.0

interface GigabitEthernet1/2
  nameif zone-ops
  security-level 70
  ip address 10.30.1.1 255.255.0.0

# OPC UA from BPCS to Operations (read-only data flow)
access-list BPCS-to-OPS extended permit tcp 10.20.0.0 255.255.0.0 host 10.30.1.50 eq 4840
# Modbus read from Operations historian to PLCs (FC 3,4 only)
access-list OPS-to-BPCS extended permit tcp host 10.30.1.50 10.20.0.0 255.255.0.0 eq 502

# Deny all other traffic between zones
access-list BPCS-to-OPS extended deny ip any any log
access-list OPS-to-BPCS extended deny ip any any log

# Apply access lists
access-group BPCS-to-OPS in interface zone-bpcs
access-group OPS-to-BPCS in interface zone-ops

# Enable Modbus protocol inspection with function code filtering
policy-map type inspect modbus MODBUS-INSPECT
  parameters
    # Allow read operations only from Operations zone
    match func-code read-coils
    match func-code read-discrete-inputs
    match func-code read-holding-registers
    match func-code read-input-registers
    # Block all write function codes
    match func-code force-single-coil  action drop log
    match func-code preset-single-register  action drop log
    match func-code force-multiple-coils  action drop log
    match func-code preset-multiple-registers  action drop log

# Apply to service policy
policy-map global_policy
  class inspection_default
    inspect modbus MODBUS-INSPECT

# Logging to OT SIEM
logging host zone-ops 10.30.1.60
logging trap informational
logging enable

# Cisco Industrial Ethernet Switch Configuration
# Zone-based VLAN assignment

# VLAN definitions aligned with zones
vlan 10
  name Z1-SIS-Safety
vlan 20
  name Z2-BPCS-Control
vlan 30
  name Z3-OPS-Operations
vlan 35
  name Z4-DMZ
vlan 40
  name Z5-Enterprise

# PLC ports - Zone 2 BPCS
interface range GigabitEthernet1/0/1-12
  description PLC connections - Zone 2
  switchport mode access
  switchport access vlan 20
  switchport port-security
  switchport port-security maximum 1
  switchport port-security mac-address sticky
  switchport port-security violation shutdown
  spanning-tree portfast
  spanning-tree bpduguard enable
  no cdp enable
  no lldp transmit

# HMI ports - Zone 2 BPCS
interface range GigabitEthernet1/0/13-18
  description HMI connections - Zone 2
  switchport mode access
  switchport access vlan 20
  switchport port-security
  switchport port-security maximum 1
  switchport port-security mac-address sticky
  switchport port-security violation restrict
  spanning-tree portfast

# Trunk to industrial firewall
interface GigabitEthernet1/0/24
  description Trunk to ISA-3000 Firewall
  switchport mode trunk
  switchport trunk allowed vlan 20,30,35
  switchport trunk native vlan 999

# Disable unused ports
interface range GigabitEthernet1/0/19-23
  shutdown
  switchport access vlan 999

#!/usr/bin/env python3
"""Data Diode Configuration Validator.

Validates that historian replication across the data diode
(Waterfall Security, Owl Cyber Defense, or Siemens) is
functioning correctly with unidirectional enforcement.
"""

import socket
import struct
import time
import json
from datetime import datetime


class DataDiodeValidator:
    """Validates data diode unidirectional enforcement."""

    def __init__(self, diode_tx_ip, diode_rx_ip, historian_port=5450):
        self.tx_ip = diode_tx_ip  # OT side (transmit)
        self.rx_ip = diode_rx_ip  # IT/DMZ side (receive)
        self.port = historian_port
        self.results = []

    def test_forward_flow(self):
        """Verify data flows from OT (TX) to DMZ (RX) through diode."""
        test_payload = f"DIODE_TEST_{datetime.now().isoformat()}"

        try:
            # Send test data to TX interface
            sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
            sock.settimeout(5)
            sock.sendto(test_payload.encode(), (self.tx_ip, self.port))
            sock.close()

            self.results.append({
                "test": "forward_flow",
                "status": "PASS",
                "detail": f"Data sent to TX interface {self.tx_ip}:{self.port}",
            })
        except Exception as e:
            self.results.append({
                "test": "forward_flow",
                "status": "FAIL",
                "detail": f"Cannot reach TX interface: {e}",
            })

    def test_reverse_flow_blocked(self):
        """Verify reverse flow (DMZ to OT) is physically blocked by diode."""
        try:
            sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
            sock.settimeout(3)
            result = sock.connect_ex((self.tx_ip, self.port))
            sock.close()

            if result != 0:
                self.results.append({
                    "test": "reverse_flow_blocked",
                    "status": "PASS",
                    "detail": "Reverse connection to OT side correctly rejected",
                })
            else:
                self.results.append({
                    "test": "reverse_flow_blocked",
                    "status": "CRITICAL_FAIL",
                    "detail": "REVERSE FLOW POSSIBLE - Data diode bypass detected!",
                })
        except (socket.timeout, ConnectionRefusedError):
            self.results.append({
                "test": "reverse_flow_blocked",
                "status": "PASS",
                "detail": "Reverse connection timed out (expected with hardware diode)",
            })

    def test_historian_replication_latency(self):
        """Measure replication latency across the data diode."""
        try:
            sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
            sock.settimeout(10)
            start = time.time()
            sock.connect((self.rx_ip, self.port))
            latency = (time.time() - start) * 1000
            sock.close()

            status = "PASS" if latency < 1000 else "WARN"
            self.results.append({
                "test": "replication_latency",
                "status": status,
                "detail": f"Replication endpoint latency: {latency:.1f}ms",
            })
        except Exception as e:
            self.results.append({
                "test": "replication_latency",
                "status": "FAIL",
                "detail": f"Cannot reach RX historian: {e}",
            })

    def run_all_tests(self):
        """Run complete data diode validation suite."""
        print("=" * 60)
        print("DATA DIODE VALIDATION REPORT")
        print("=" * 60)

        self.test_forward_flow()
        self.test_reverse_flow_blocked()
        self.test_historian_replication_latency()

        for r in self.results:
            status_icon = "+" if r["status"] == "PASS" else "-"
            print(f"  [{status_icon}] {r['test']}: {r['status']}")
            print(f"      {r['detail']}")

        return self.results


if __name__ == "__main__":
    validator = DataDiodeValidator(
        diode_tx_ip="10.30.1.100",   # Operations zone TX
        diode_rx_ip="172.16.1.100",  # DMZ zone RX
    )
    validator.run_all_tests()

# Validation test from Enterprise zone - should be blocked from reaching BPCS
nmap -sT -p 502,44818,102,4840 10.20.0.0/16 --reason
# Expected: All ports filtered/closed

# Validation test from Operations zone - read-only Modbus should work
python3 -c "
from pymodbus.client import ModbusTcpClient
client = ModbusTcpClient('10.20.1.10', port=502)
client.connect()
# Read should succeed
result = client.read_holding_registers(0, 10, slave=1)
print(f'Read test: {\"PASS\" if not result.isError() else \"FAIL\"}')
# Write should be blocked by firewall
result = client.write_register(0, 100, slave=1)
print(f'Write blocked: {\"PASS\" if result.isError() else \"FAIL - WRITE PERMITTED!\"}')
client.close()
"

# Verify data diode blocks reverse traffic
ping -c 3 10.30.1.100  # From DMZ to OT - should timeout
# Expected: 100% packet loss (hardware diode blocks ICMP)