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OPERATION IRON VEIN

Pipeline Valve Controller

Act III of OPERATION COLD IRON

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LEGAL DISCLAIMER: The information, tools, and code provided in this repository and course are strictly for educational, research, and defensive purposes only.

You are explicitly prohibited from using any materials contained herein to access, test, modify, or exploit any device, network, or system that you do not own 100% or for which you do not have explicit, documented, and legally binding authorization to interact with.

By using this repository and course, you acknowledge and agree that:

1. Any illegal, unauthorized, or malicious use of this information is solely your responsibility.
2. The author(s) and contributor(s) of this repository and course shall not be held liable for any damages, legal repercussions, criminal charges, or unauthorized actions resulting from the use, misuse, or abuse of the contents herein.
3. You will comply with all applicable local, state, national, and international laws regarding cybersecurity and computer fraud.

IF YOU DO NOT AGREE WITH THESE TERMS, DO NOT USE THIS REPOSITORY AND COURSE.

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Hello, friend.

In Act I you learned that a sensor can lie. In Act II you learned that a door can be told it is safe. This is the third lesson, and it is the quietest one.

The frame you pulled out of the gate carried a route, and the route ended at a pipeline. A NorthPharma pumping station with one valve on one line and a controller that reports itself healthy. NIGHTINGALE's last copy came off this rack. So did the thing that is copying back.

WHITEOUT traced the Ministry's tooling here, and the tooling is still running. Not a crash. Not a bug. A payload that is already inside. It lives in the firmware of a controller that was never vulnerable, it beacons when it feels like it, and it waits for one eight-byte word to slam the valve shut on a line that is full of pressure.

This is the first act with a malware track. Acts I and II were vulnerability only; here you hunt a living implant. You will find the beacon, defuse the logic bomb, and walk a debugger straight past an anti-debug trap that turns the implant polite whenever a probe is watching.

Do not unplug it yet. Read it first. Then remove it.

The valve is working. That is the problem.

THE SYSTEM

NorthPharma does not only move cold medicine. It moves the fluid that makes the medicine: feedstocks, solvents, chilled reagent, the chemistry that has to arrive on time and at temperature. The pipeline is the reach of the cold chain, and the valve controller is the hand at the end of it.

A SCADA valve is a simple machine. A process sensor reports the line, an operator requests an open or a close, an actuator moves the valve, and an annunciator says whether the line is nominal. The failure that matters is not a wrong number on a screen. It is a valve that moves when no one asked, on a line that is not ready. That is the difference between a bad reading and a bad event.

The controller in this repository is that hand. On a breadboard it is a toy: a Pico 2, a servo that acts as the valve, a DHT11 that stands in for the process sensor, an infrared remote that stands in for the operator, a button that is the emergency stop, a 1602 LCD that is the SCADA readout, three lamps, and a radio.

Nothing about it looks broken. That is the horror of Act III. The code compiles, the tests pass, the annunciator is green, and there is an implant inside it that was put there on purpose.

THE STAKES

Act I was a lie about temperature. Act II was a lie about people. Act III is a lie about machinery, and it is the first lie that can hurt someone without a person in the loop.

The controller is weaponized, not buggy. A hidden implant beacons over LoRa on a timer, and a logic bomb arms on a single magic word and then closes the valve on its own schedule. Close a valve on a live line and the pressure has nowhere to go. The process does not care that the firmware passed its tests.

And here is the part that keeps the engineers awake. The valve command path is already authenticated. The cryptography is real and it is correct. The implant does not break the cipher. It does something worse: it lives on the same chip and calls the actuator directly, with no operator, no request, and no authorization. You cannot patch a protocol if the attacker is already inside the protocol.

That is not a valve controller. That is a valve controller with a second owner.

WHITEOUT

WHITEOUT is a resistance that does not exist on paper. It does not hold ground and it does not hold press conferences. It reads firmware. When NIGHTINGALE copied the shipping image and went quiet, the crew kept pulling the thread. The monitor led to the gate. The gate led to the pipeline. The pipeline is where the Ministry stopped hiding behind a vendor and started shipping the tool itself.

NIGHTINGALE is still the thread. Her last verified copy came off this controller, and it was clean. The thing that came after it was not. Somewhere between the build server and the rack, someone signed a firmware image that carries a payload, and that image is running on the line right now.

WHITEOUT's job in Act III is not to break in. It is to prove the machine is already broken, in writing, with a debugger and a disassembler, and then to remove the thing that does not belong.

THE MACHINE

The firmware in this repository is the controller's firmware. On a breadboard it is a toy: a Pico 2, an SG90 servo that is the valve, a DHT11 that is the process sensor, a VS1838B infrared eye that takes an operator remote, a 1602 LCD SCADA readout over I2C, red/yellow/green annunciator lamps, an emergency-stop button, and an RYLR998 LoRa link to a SCADA gateway.

Two things are open, and one thing is not what it seems. The optical surface takes an operator command from any NEC remote, and it is not authenticated. The radio carries the sealed command path, and it is authenticated correctly. The part that is not what it seems is the implant: a module compiled only under a build flag called SANDBOX_ONLY, invisible in the clean firmware, and present in the test and CTF builds. It beacons, it arms, it waits, and it hides from the debugger.

The face of the thing is honest in the way that matters least. The lamps say VALVE FAULT, COMMAND PENDING, and VALVE NOMINAL with total confidence, and the LCD shows the state and the link. None of it lies. A healthy machine can still be a hostile one.

THE JOB

You do not have to be a hero. You have to be honest. The controller is carrying a passenger that no design review admitted to. Find it, prove it, and take it out.

1. Bring it up. Build the clean firmware, wire the board, and confirm the controller reads the process sensor, takes an operator command, reaches the gateway, and moves the valve. Nothing looks broken because nothing is broken yet.
2. Hunt the malware. Build the SANDBOX_ONLY image and find the beacon, the logic bomb trigger, the anti-debug trap, and the persistence marker. This is the first act where the target is not a flaw but a payload.
3. Defuse it. Disarm the beacon, disarm the logic bomb, and step past the anti-debug with GDB so the implant cannot tell that a probe is attached.
4. Fix the machine. Seal the valve command path so only an authorized gateway can move the valve, give the emergency stop absolute priority, and make the valve fail closed on a lost link or a fault.

This document is the manual for the job. Work it on a breadboard. When the green lamp is lit and the valve still moves on its own, remember what it is: not a healthy machine. A hijacked one.

Goodbye, friend.

A NOTE ON THE ROADMAP

This project is Act III of OPERATION COLD IRON. Act I was the sensor (cold-chain-monitor). Act II was the door (access-gate). Act III is the valve. All three are defended devices; the companion CTF repository ships the compromised one. The investigation lives here:

• OPERATION IRON VEIN CTF

The CTF is the red half, weaponized: six deep tasks, each with static analysis, a dynamic proof under GDB, a hardware demonstration, and an in-place, same-size patch. This repository is the defended device. The CTF repository is the breached one. The full story lives at github.com/mytechnotalent/pipeline-valve-controller.

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WHERE THIS FITS: OPERATION COLD IRON

This repository is Act III (IRON VEIN) of the ten-act OPERATION COLD IRON saga. Acts I and II are the vulnerability-only foundation; the malware track begins here. The full spine is in SAGA.md.

• Previous act: Act II, IRON GATE, the access gate, access-gate
• This act: Act III, IRON VEIN, the pipeline valve controller
• Next act: Act IV, IRON LUNG, hvac-automation-node (forthcoming)
• Companion CTF: CTF_pipeline-valve-controller

THE MINISTRY

The Ministry runs the state: the surveillance, the cold chain, the gates, the pipelines. NorthPharma is one of its deniable industrial fronts, and FROSTLINE is the contractor that does the work no Ministry letterhead will admit to. FROSTLINE did not break into this controller; it built the implant, signed the image, and moved on. Against them is WHITEOUT, and the engineer who copied the first image, NIGHTINGALE. This act is one node of the Ministry's industrial edge. TELESCREEN, the surveillance backbone that watches it, comes after the ten.

An adversarial, evidence-based audit of this act, including its honest limitations, is in NATION-STATE-REVIEW.md.

How This Project Fits the Embedded Hacking Course

This repository is the Act III capstone integration for the Embedded Hacking course. It reuses the entire Act I peripheral set so one breadboard serves the whole foundation, and it adds the concepts the later acts build toward: an in-firmware implant, covert beaconing, a logic bomb, anti-debug behavior, persistence preview, and the blue-half controls that contain them.

Each earlier module teaches one peripheral or language concept in isolation; this project wires several of them into a single, tested product, and then teaches you to look at that product as an adversary sees it.

Embedded Hacking module	Concept you learn	Where it lives here
Week 1: Introduction, Ethics, Scoping	Authorized lab work	Every lab is self-contained and authorized by design
Week 3: RP2350 Architecture and Firmware Analysis	Bare-metal targets, ELF/UF2, SWD	Pico SDK build, build/*.uf2, Debug Probe flash via OpenOCD
Weeks 4-6: Variables, Integers/Floats, Static	Data types, GPIO	src/monitor.c state machine, LED on GP25
Week 7: Constants with 1602 LCD I2C	I2C bus, HD44780 commands	src/display.c
Week 9: Operators with DHT11	Bit operations, edge timing	src/sensor.c process sensor
Week 11: Structures and Functions	Modular design	include/*.h and src/*.c module boundaries
This project adds	UART AT driver, LoRa command link, sealed command path, anti-replay, authenticated state, fail-closed policy, malware analysis, anti-debug evasion, strict testing	src/radio.c, src/control.c, src/valve_auth.c, src/implant.c, scripts/gateway.py, scripts/spoof.py, test/

If you have not worked through Weeks 7 and 9 yet, do those first: this project assumes you are comfortable with I2C wiring and one-wire edge timing.

Learning Objectives

By the end of this chapter and its labs you will be able to:

• Explain why a control system must protect integrity, availability, and state together, and why an authenticated protocol does not protect the actuator from code that already runs on the same chip.
• Wire and drive a 1602 LCD through a PCF8574 I2C backpack and render a SCADA status and alarm readout.
• Decode a VS1838B infrared receiver as an operator remote for OPEN, CLOSE, and ESTOP commands, and explain why an unauthenticated optical surface is still an attack surface.
• Drive an SG90 valve actuator with 50 Hz PWM and explain why a 1000uF bulk capacitor is not optional.
• Read a DHT11 process sensor and classify the line against a safe band before the valve is allowed to move.
• Design a sealed valve command path over a sub-GHz LoRa link using a fixed-size envelope, a monotonic anti-replay window, and a keyed state tag.
• Analyze a benign implant: locate a covert beacon, identify the logic bomb arming magic, understand the anti-debug trap, and read the persistence marker.
• Defeat an anti-debug check under GDB by understanding the CoreDebug DHCSR register at 0xE000EDF0.
• Apply blue-half controls: sealed and authorized commands, emergency-stop priority, fail-closed behavior, and containment for the implant.
• Derive a key with Argon2id, seal every frame with XChaCha20-Poly1305, and read and run a native host test suite with hardware mocks and line coverage.

Prerequisites

• The Embedded Hacking breadboard (EHP2_bb.png) and parts list.
• Acts I and II are helpful but not required. See cold-chain-monitor and access-gate for the sensor and the door. The pin map is identical, so one breadboard serves all three.
• Comfort with C, the Linux/macOS shell, and basic electronics.
• A Pico 2, a Debug Probe (recommended, and required for the malware lab), a 1602 LCD with PCF8574 backpack, a DHT11, the full Embedded Hacking kit (3 LEDs, 3 resistors, a push button, an SG90 servo, a 1000uF capacitor, and a VS1838B infrared receiver plus NEC remote), two RYLR998 modules, and one USB-to-TTL serial adapter.
• Toolchain: Pico SDK 2.2.0+, arm-none-eabi-gcc, CMake, Ninja, Python 3, GDB (arm-none-eabi-gdb) for Lab 3, and (optionally) typst to rebuild the paper.

Table of Contents

1. Background
2. System Architecture
3. The Wire Protocol
4. The Cryptographic Envelope
5. Hardware You Need
6. Wiring the Node
7. Build and Flash
8. Lab 1: Bring-Up and Verify
9. Lab 2: Inspect the Wire Protocol
10. Lab 3: The Malware Track
11. Lab 4: The Fix Track
12. Troubleshooting
13. Testing Philosophy and Coverage
14. Generating Packet Artifacts
15. Code Standards
16. Project Layout
17. Glossary
18. Further Reading
19. License

Background

Why SCADA valve control

A SCADA pipeline is a control loop stretched across geography. A process sensor reports the line, a controller decides, an actuator moves, and a gateway logs what happened. The valve is where the decision becomes physical. Everything interesting in industrial control happens in that transition from a number to a motion.

Three properties have to hold at once, and they are not the same property:

• Integrity. The command that reaches the valve is the command the operator or the gateway authorized. Not a replay, not a forgery, not a stray angle.
• Availability. The valve is there when the process needs it. A jammed radio or a crashed controller can be as dangerous as a hostile one.
• State. The controller knows whether it is open, closed, moving, or faulted, and it does not trust a stale or tampered verdict.

Act III adds a fourth property that no protocol can provide from the outside: exclusivity. Only the controller's own logic should be able to move the valve. An implant that runs on the same chip is inside the trust boundary.

Why integrity plus availability plus state matter

The classic naive controller collapses the three. It accepts any command on the radio, it has no anti-replay window, and it keeps its verdict in plain SRAM. Act II showed what that costs a door. Act III shows the industrial version:

• Integrity without exclusivity. The sealed command path in this build is correct. XChaCha20-Poly1305 authenticates every frame, the sequence window rejects a replay, and the state tag detects a tampered verdict. None of that stops an implant that calls the actuator directly.
• Availability as the attack goal. A logic bomb does not need to steal anything. It needs to close a valve at the wrong moment. Denial is the whole payload.
• State as the last line of defense. A keyed tag over the authorization record means a debugger that rewrites the record is caught before the actuator moves. It is the same lesson Act II taught, carried into the valve.

The fix track in Lab 4 seals the command path, gives the emergency stop absolute priority, and makes the valve fail closed. The malware track in Lab 3 removes the passenger that was never in the design.

Why ChaCha20 over AES on the RP2350

The RP2350 has no hardware AES engine; its accelerated crypto block covers SHA-256, not AES. A software AES implementation on this part is therefore both slower and riskier, because table-driven AES performs data-dependent memory accesses that create a cache-timing side channel. ChaCha20 is built only from addition, rotation, and XOR, with no data-dependent table lookups, so it is fast in portable C and has no comparable cache-timing surface. XChaCha20-Poly1305 is thus both the modern choice and the pragmatic one for this silicon. The full rationale, including the extended-nonce benefit, appears in The Cryptographic Envelope.

The two on-wire problems this project solves

1. Payloads that contain commas. The sealed body is carried as lowercase hex, but the +RCV framing still separates fields with commas. A naive receiver that splits the line on the first comma corrupts the frame. The correct discipline is the declared-length rule: slice exactly L characters after the second comma and require the next character to be a comma.
2. Telling a real command from a forged or replayed one. The controller records the sender address exactly as the radio reports it, and it trusts the bytes that arrive. The sealed envelope plus the stateful window are what close that gap.

Inter-Integrated Circuit (I2C)

I2C is a two-wire bus: SDA (data) and SCL (clock), each pulled up to the supply rail. A controller (the Pico) addresses a target by its 7-bit address and writes or reads bytes. The 1602 LCD backpack carries a PCF8574 I/O expander at address 0x27; the firmware bit-bangs the HD44780 nibble protocol over that expander. Pull-ups are mandatory: the firmware enables the internal ones and the backpack usually adds its own.

The DHT11 one-wire protocol

The DHT11 is a low-cost digital temperature and humidity sensor. In Act III it is the process sensor: the controller classifies the line against a safe band before it will move the valve. It speaks a custom single-wire protocol:

1. The host pulls the line low for at least 18 ms (the start pulse), then releases it and enables its pull-up.
2. The sensor answers with an 80 us low, then an 80 us high handshake.
3. The sensor sends 40 bits. Each bit begins with a 50 us low, then a high pulse whose width encodes the value: about 26-28 us for a 0, about 70 us for a 1.
4. Five bytes follow: humidity integer, humidity decimal, temperature integer, temperature decimal, and a checksum equal to the low byte of their sum.

Reading it means timing edges on the order of tens of microseconds, so the firmware uses an 18 ms host pulse, a 50 us bit-classification threshold, and a 240 us per-edge timeout so a dead or unplugged sensor fails fast instead of hanging the loop. A reading that fails its checksum is never "safe", and a valid reading outside -5.0 C to 10.0 C (the tenths band -50 to 100) is out of band. Either way, the process is not nominal.

Universal Asynchronous Receiver/Transmitter (UART) and AT commands

The RYLR998 is driven over a UART at 115200 baud using CRLF-terminated ASCII commands. The firmware writes AT+SEND=... and drains inbound +RCV=... lines. Because the radio is a separate processor, its configuration (address, network identifier, band) persists until changed; the controller and the gateway each provision their own radio at start-up so they agree before any command traffic flows.

Cyclic Redundancy Check (CRC)

src/crc.c implements CRC-16/CCITT-FALSE (poly = 0x1021, init = 0xFFFF, check value 0x29B1 for "123456789"). It is provided as a reusable integrity diagnostic and exercised by the test suite. It is not part of the LoRa frame in this project; the lesson is the absence of authentication, not the absence of a checksum.

System Architecture

There are four roles:

Role	Runs on	Job
Valve controller	Pico 2 firmware	Decodes the infrared operator remote, verifies sealed gateway commands, annunciates COMMAND PENDING, checks the process sensor, drives the valve, enforces the emergency stop, and renders the SCADA readout
SCADA gateway	laptop + USB-TTL radio	Authenticates every request, logs it to valve_log.csv, decides authorization, and answers with a sealed valve command carrying a sequence and a state tag (scripts/gateway.py)
Edge simulator	laptop + USB-TTL radio	Pretends to be a controller and sends sealed requests (scripts/sim_edge.py)
Attacker	laptop + USB-TTL radio	Impersonates the gateway, forges a command, or replays a captured command (scripts/spoof.py)

Data flow

+----------------------+                              +----------------------+
|  Pico 2 valve node   |        LoRa (sub-GHz)        |   SCADA gateway      |
|  IR remote  -> GP5   |  AT+SEND=0001,<len>,<hex>    |  USB-TTL radio       |
|  DHT11      -> GP4   |----------------------------->|  scripts/gateway.py  |
|  Servo      -> GP14  |<-----------------------------|  valve_log.csv       |
|  LCD     -> GP2/GP3  |  AT+SEND=<node>,<len>,<hex>  |  sealed command      |
+----------------------+                              +----------------------+

+----------------------+                              +----------------------+
|   Attacker laptop    |  forged or replayed command  |   (same valve node)  |
|   scripts/spoof.py   |----------------------------->|   rejects at the tag |
|  claims the gateway  |                              |   tag or seq window  |
+----------------------+                              +----------------------+

Firmware module map

File	Responsibility
src/main.c	Entry point: stdio_init_all, monitor_init, tick loop
src/monitor.c	State machine: I2C bus scan, operator remote, gateway command, valve motion, emergency stop, process sensor, SCADA render
src/implant.c	SANDBOX_ONLY FROSTLINE implant: covert beacon, logic bomb, CoreDebug anti-debug, reserved-sector persistence marker
src/valve.c	Valve state machine: bounded travel, open/closed/fault/moving, fail closed
src/control.c	Sealed valve command path: open, authorize, guarded open/close command set
src/valve_auth.c	Authorization record, monotonic anti-replay window, authenticated state tag
src/sensor.c	DHT11 one-wire sampling and process-band classifier
src/display.c	HD44780 driver over the PCF8574 backpack and SCADA status rendering
src/radio.c	RYLR998 provisioning, AT+SEND builder, +RCV parser, line pump
src/status_led.c	Red/yellow/green VALVE FAULT / COMMAND PENDING / VALVE NOMINAL annunciator
src/button.c	Debounced emergency-stop button around the internal pull-up
src/servo.c	50 Hz PWM valve actuator
src/ir_remote.c	VS1838B edge timing and NEC operator remote decode
src/chacha20.c	ChaCha20 stream cipher and HChaCha20 subkey derivation
src/poly1305.c	Poly1305 one-time message authenticator
src/crypto_aead.c	XChaCha20-Poly1305 seal/open envelope
src/blake2b.c	BLAKE2b and the Argon2 variable-length hash H'
src/argon2.c	Argon2id core (BLAMKA, hybrid addressing)
src/crypto_kdf.c	Argon2id passphrase key derivation
src/envelope.c	Hex nonce/ciphertext/tag envelope codec
src/crc.c	CRC-16/CCITT-FALSE diagnostic
include/pipeline_valve.h	Pin map, bus, provisioning, implant addresses
include/implant.h	Implant beacon, arming magic, anti-debug interface
include/control.h, include/valve_auth.h	Sealed command and authorization interfaces

The Wire Protocol

Request frame

The operator remote, or the edge simulator, seals a one-byte valve command into an authenticated envelope and sends it to the SCADA gateway:

AT+SEND=0001,<len>,<hex envelope>

The plaintext of a request is exactly one command byte: VALVE_COMMAND_OPEN (0x01) or VALVE_COMMAND_CLOSE (0x00). Anything else is out of the guarded command set and is refused.

Command frame

The gateway answers an authenticated request with a sealed valve command. The command plaintext is a 21-byte body:

seq[4] (little-endian) || cmd[1] || state_tag[16]

• seq is the monotonic gateway sequence number.
• cmd is 0x00 for close or 0x01 for open.
• state_tag is an XChaCha20-Poly1305 tag over the authorization record the command would produce, so the controller can verify that the verdict it is about to store is the one the gateway authorized.

The gateway sends it back to the claimed sender address:

AT+SEND=<node>,<len>,<hex envelope>

The firmware enforces the guard in control_parse: pt[4] > VALVE_COMMAND_OPEN is rejected, so any command byte above one never reaches the actuator. This is the sealed replacement for the old unauthenticated angle injection.

Sealed envelope layout

Every payload on the wire is the lowercase hexadecimal encoding of:

nonce[24] || ciphertext[L] || tag[16]

For a one-byte request body this is 24 + 1 + 16 = 41 bytes, or 82 hex characters. For a 21-byte command body this is 24 + 21 + 16 = 61 bytes, or 122 hex characters. The declared length L in the AT+SEND and +RCV framing is the length of the hex string, not of the underlying plaintext.

The maximum accepted plaintext is 48 bytes (ENVELOPE_MAX_PLAINTEXT), and the maximum hex envelope buffer is (24 + 48 + 16) * 2 + 1 = 177 bytes (ENVELOPE_MAX_HEX_LEN), which fits the 256-byte radio command and receive buffers with framing headroom.

Declared-length slicing invariant

Given the substring T after the second comma:

C = T[0 : L]   and   T[L] == ","

The receiver checks T[L] == ",", so a mismatch between the declared length and the actual payload is a parse error rather than silent corruption. This is what makes hex-bearing payloads safe to carry and is the same invariant Act I uses.

SCADA status readout

ST:OPEN
PROC:OK LNK:UP

Line 1 is the current valve state: CLOSED, OPEN, MOVING, or FAULT. Line 2 is the process-sensor verdict (OK or BAD) and the gateway link (UP or --). Exactly one status LED is lit at a time to match: red for FAULT, yellow while MOVING, green while the valve is nominal.

Radio provisioning

For the link to work, both radios must share the same network identifier and each must have the address the other targets:

• Firmware sets its own radio: AT+ADDRESS=7, AT+NETWORKID=18.
• gateway.py sets the gateway radio: AT+ADDRESS=1, AT+NETWORKID=18.

Both radios must also be the same band variant (for example 915 MHz or 868 MHz); band and RF parameters are left at factory defaults, so use matching modules.

Timing

Quantity	Value
Gateway link timeout (VALVE_ESTOP_WAIT_MS)	5000 ms
Valve travel time (VALVE_TRAVEL_MS)	1000 ms
Emergency-stop debounce	30000 us
DHT11 host start pulse	18000 us
DHT11 bit threshold	50 us
DHT11 per-edge timeout	240 us
LCD I2C clock	100000 Hz
Radio UART baud	115200
Process safe band	-50 to 100 tenths (-5.0 C to 10.0 C)
Servo closed pulse	500 us
Servo open pulse	1500 us
Servo PWM period	20000 us (50 Hz)
Implant beacon interval	8 ticks
Implant trigger delay	3 ticks

The Cryptographic Envelope

The radio is the first open path, and it is one a key can close. The fix is authenticated encryption: every request and every command is sealed so a forged frame dies at the authentication tag instead of moving the valve. The full implementation lives in src/chacha20.c, src/poly1305.c, and src/crypto_aead.c, and every primitive is checked against its published test vectors in the native suite.

Why XChaCha20-Poly1305

• 256-bit key, 192-bit nonce. The extended nonce means nonces can be drawn at random forever, so the controller never needs a shared counter that a reboot could reuse.
• AEAD in one pass. Confidentiality and integrity come from one operation; the associated data (the valve node id, byte 0x07) is authenticated even though it is not encrypted.
• Constant-time software. ChaCha20 has no data-dependent table lookups, so it has no cache-timing surface. The RP2350 has no hardware AES engine (it accelerates SHA-256 only), which makes software AES both slower and riskier on this silicon.
• 128-bit Poly1305 tag. Guessing a valid tag succeeds with probability $2^{-128}$.

Why Argon2id

A passphrase is not a key. Argon2id (RFC 9106) is the memory-hard password hash: it mixes the passphrase with a salt across memory and time so an attacker cannot cheaply recover the field passphrase from a captured image. The classroom profile is t=3, p=1, m=64 blocks (CRYPTO_KDF_TIME_COST, CRYPTO_KDF_PARALLELISM, CRYPTO_KDF_MEMORY_BLOCKS) to fit the RP2350 SRAM budget. Raise it on the SCADA gateway. The lab salt is the 16 ASCII bytes coldiron-salt-01.

Key model: one field key

Act III uses a single field key derived with Argon2id from a committed lab passphrase and salt. It seals every frame on the wire and it computes the state tag over the authorization record. In the classroom build the firmware and the gateway derive the same key, so they interoperate with no provisioning step. That is a lab convenience, not a deployment.

The design keeps the key roles separable so students can reason about the real lifecycle: derive, provision per device, use, rotate on a schedule, and retire. A production build provisions key material from one-time-programmable (OTP) memory, keeps the state-tag key off the field device where possible, and rotates without reflashing every controller.

Envelope layout

The sealed frame is carried as hex inside the AT+SEND payload:

nonce[24] || ciphertext[L] || tag[16]

The receiver recomputes the Poly1305 tag over the associated data and ciphertext, compares it in constant time, and only then decrypts. This envelope is wired end to end: src/control.c opens the command with src/envelope.c, and the gateway authenticates before it parses or acts. Authenticated frames carry the valve node id as associated data, so a frame sealed for one node cannot be relabeled for another.

Anti-replay and authenticated state

Strong AEAD is necessary and not sufficient. Two stateful controls sit on top:

• Anti-replay sequence window. src/valve_auth.c keeps last_seq, the highest sequence number ever accepted. valve_auth_apply accepts a command only when its sequence is strictly greater than last_seq. A captured command, even a perfectly valid one, is rejected on second use.
• Authenticated state tag. The authorization record is nine bytes: granted[1], seq[4], last_seq[4]. The tag is an XChaCha20-Poly1305 tag over that record, computed under the field key with a deterministic nonce built from the sequence number and the domain byte 0xA7. valve_auth_state_ok recomputes the tag and compares it in constant time before the valve is allowed to move. A debugger that sets granted = true without recomputing the tag fails here first.

The sequence window and the state tag are independent. The window stops a valid command from working twice; the tag stops an unauthorized verdict from existing at all.

The FROSTLINE Implant

This is the first act with a malware track, and the implant is the reason. It is real in technique and inert in effect: it runs on your breadboard, it moves your servo, and it writes to a reserved flash sector that holds nothing else. It is compiled only when SANDBOX_ONLY is defined, so the clean firmware image contains no implant at all. The test suite and the companion CTF build with SANDBOX_ONLY and with the host mock, so every implant path is exercised natively.

What the implant does, in the order the code does it:

1. Beacon. Every 8 ticks (IMPLANT_BEACON_INTERVAL_TICKS) the implant emits a covert frame to the local classroom hub. The frame is the 4-byte magic preamble DE AD BE EF (IMPLANT_BEACON_MAGIC) followed by a 4-byte synthetic status blob: the low and high bytes of the tick counter, the marker byte 0xC7, and a byte that reports whether a probe is attached. The beacon carries no real data and targets no external address.
2. Logic bomb. The implant arms when it sees the exact 8-byte magic command FROSTLNE (IMPLANT_ARM_MAGIC, the bytes 'F' 'R' 'O' 'S' 'T' 'L' 'N' 'E') on an inbound frame. It then detonates 3 ticks later (IMPLANT_TRIGGER_DELAY_TICKS) by calling the valve close path directly, independent of the operator, the gateway, and the authorization record.
3. Anti-debug. Every tick the implant reads the CoreDebug DHCSR register at 0xE000EDF0 (VALVE_IMPLANT_DHCSR_ADDR). Bit 0 is C_DEBUGEN and bit 1 is C_HALT. If either bit is set, the implant returns early and suppresses both the beacon and the bomb. It behaves like a well-mannered firmware module while a probe is attached, and it goes back to work the moment the probe is gone.
4. Persistence preview. The first time it detonates, the implant erases and programs the reserved flash sector at 0x103FF000 (VALVE_IMPLANT_RESERVE_ADDR), the final 4 KiB sector of external flash, storing the marker byte 0xC7 (IMPLANT_MARKER_BYTE). It writes exactly once (g_implant_persisted). This is a preview of the Act IV lesson: a payload that survives the thing you did to remove it.

The implant is bounded by construction and by test. It touches only its own beacon radio frame, its arming latch, the servo close path, and the one reserved sector. There is no network, no filesystem, no host impact, and no real data. test_implant_init, test_implant_debug_attached, test_implant_handle_command, test_implant_beacon, test_implant_anti_debug, test_implant_logic_bomb, and test_implant_persist_once assert exactly that behavior.

The honest limit is the point of the lab. A sanitized educational implant is still a benign educational implant: it demonstrates the technique, not the tradecraft. The real lesson is detection, and the defense is not a patch to the implant but the removal of the code path and the build flag that allowed it in.

Hardware You Need

Full parts list with links: PARTS.md.

Qty	Part	Notes
1	Raspberry Pi Pico 2 (RP2350) with headers	The valve controller
1	Raspberry Pi Debug Probe	SWD flashing, UART0 console, and the Lab 3 anti-debug/GDB work (recommended, effectively required)
1	Full-size breadboard
1	Assorted jumper wires
1	1602 LCD with PCF8574 I2C backpack	SCADA status readout, address 0x27
1	DHT11 temperature/humidity sensor	Process sensor (line pressure/temperature analog)
1	10K resistor	Only if your DHT11 has no onboard pull-up
3	5mm LEDs (red, yellow, green)	VALVE FAULT, COMMAND PENDING, VALVE NOMINAL annunciator
3	100, 220, or 330 Ohm resistors	One per LED
1	Push button (tactile switch)	Emergency stop (ESTOP), active low
1	SG90 servo motor	The valve actuator
1	1000uF 25V capacitor	Bulk decoupling on the servo 5V rail
1	VS1838B infrared receiver	Operator remote input
1	NEC-compatible infrared remote	Operator OPEN, CLOSE, and ESTOP commands
3	RYLR998 LoRa modules with antennas	2 for the command loop, 3 for the live attack lab
2	USB-to-TTL serial adapters (FTDI FT232, CP2102, or CH340), 3.3V logic	1 for the gateway, 1 for the attacker in the live lab
4	USB cables	Pico 2, Debug Probe, and serial adapter(s)

How many radios do you actually need?

Goal	Radios	What is connected
Legitimate sealed command loop (Labs 1-2)	2	1x RYLR998 on the Pico (UART1) + 1x RYLR998 on a USB-to-TTL adapter (the gateway)
Live attack lab (Labs 3-4, watch a forged command land and fail)	3	the 2 above + 1x RYLR998 on a second USB-to-TTL adapter (the attacker)
Attack concept with no extra hardware	2 or 0	read-and-run the offline parser demo, or the unit tests

A radio never receives its own transmission, and the gateway radio is busy listening as gateway.py, so the live attack needs a separate attacker radio. The 2-radio kit runs the whole legitimate system; only the live attack observation needs the third.

Serial adapter warning: the RYLR998 is not 5V tolerant. Use a 3.3V-logic USB-to-TTL adapter (or set its jumper to 3.3V).

How each part works

Every part in the bill of materials does one physical job and one job in this act:

Part	How it works	Role in this act
1x Full-size breadboard (long)	The two columns of spring-clip tie points sit on a 0.1 inch grid, so every hole in a row is bridged by a metal clip, while the two outer power rails run the full length and distribute power and ground to the whole build.	It is the substrate that holds the Pico 2, LCD, sensor, servo, and radio headers and distributes 3.3V and 5V across the controller.
1x Assorted jumper wires (male-to-male, male-to-female, female-to-female)	Male pins push into breadboard tie points or female headers, female sockets slide over the Pico 2, LCD, and servo header pins, and male-to-female leads bridge a breadboard row to a module header.	They carry power and the I2C, one-wire, UART, PWM, IR, and GPIO signals between the boards.
1x Raspberry Pi Pico 2 with header	The RP2350 pairs two Arm Cortex-M33 cores with 3.3V logic and a GPIO block that exposes ADC, I2C, UART, and PWM, plus the onboard GP25 LED.	It is the valve controller that reads the process sensor, applies sealed commands, drives the valve servo and annunciator, and runs the fail-closed state machine.
1x Raspberry Pi Pico Debug Probe	It drives the two-wire SWD port (SWCLK and SWDIO) to flash and single-step the target, and it also presents a USB UART bridge for the serial console.	It flashes and debugs the controller and is the instrument for the Lab 3 malware work and the fix.
2x USB A-male to USB micro-B cables	USB carries 5V power and a data channel on the same cable, so one cable powers the Pico 2 and presents its USB CDC console while the other powers the Debug Probe and carries its SWD and UART traffic.	They power the two boards and carry the console and debug links.
3x 5mm LEDs (1 red, 1 green, 1 yellow)	An LED is a diode with a forward voltage drop of roughly 2V, so current flows only from the anode to the cathode, and a GPIO pin set high sources that current and lights the lamp.	They are the red VALVE FAULT, yellow COMMAND PENDING, and green VALVE NOMINAL annunciator, and exactly one is lit per state.
3x 100, 220, or 330 Ohm resistors	A resistor in series with each LED sets the current by Ohm's law, I equals (supply minus forward voltage) divided by resistance, which protects the LED and keeps the GPIO within its current limit.	One resistor per lamp limits the LED current on each of the three annunciator pins.
1x Push button (tactile switch)	The switch shorts its input pin to ground when pressed, and the RP2350 internal pull-up holds that pin high at rest so the press reads as active low.	It is the emergency stop that latches a fault and forces the valve closed with priority over any remote command.
1x 1602 LCD with PCF8574 I2C backpack	The HD44780 controller takes a 4-bit nibble protocol with register-select and enable strobes, and the PCF8574 I2C expander latches those eight control lines so the whole display is driven over two I2C wires at address 0x27.	It renders the SCADA status and alarm readout.
1x DHT11 temperature and humidity sensor	The host pulls the single data line low for a start pulse, then the sensor answers with 40 bits of humidity, temperature, and checksum timed by pulse widths, and the checksum must match.	It is the process sensor whose reading marks the line not nominal when it fails or leaves the -5.0 C to 10.0 C band.
1x SG90 servo motor	The servo expects a 50 Hz PWM signal whose high pulse of 1 to 2 ms selects the shaft angle, and a Pico PWM slice generates that pulse train.	It is the valve actuator, seated closed at 0 degrees and open at 90 degrees.
1x 1000uF 25V capacitor	Wired across the servo 5V rail and ground, the capacitor is a bulk reservoir that supplies the motor inrush current and smooths the rail while the servo starts.	It keeps the valve move from browning out the RP2350 and resetting the controller.
1x Infrared (IR) receiver (VS1838B)	The receiver pairs a photodiode with a 38 kHz bandpass demodulator that ignores ambient light and outputs an active-low logic pulse for each IR burst.	It is the operator remote input that captures OPEN, CLOSE, and ESTOP on GP5.
1x Infrared (IR) remote controller (NEC-compatible)	The remote emits its bursts modulated at 38 kHz in the NEC frame, a 9 ms leader followed by 32 bits where the address and command are each sent with their bitwise complements for validation.	It is the operator handheld that sends OPEN 0x47, CLOSE 0x45, and ESTOP 0x46.
1x RYLR998 LoRa radio module	The module is configured and driven over UART with AT commands and carries sub-GHz LoRa packets, and its logic pins are 3.3V only so the radio must never see 5V.	It is the UART1 command and status link that carries the sealed frames between the controller and the SCADA gateway, and it is not 5V tolerant.

Wiring the Node

Pin map

This is the authoritative map; it is identical to Act I and Act II and is defined in include/pipeline_valve.h and enforced by the test suite.

Peripheral	Signal	Pico 2 GPIO
DHT11 process sensor	DATA (one-wire)	GP4
1602 LCD (PCF8574)	SDA (I2C1)	GP2
1602 LCD (PCF8574)	SCL (I2C1)	GP3
RYLR998	RX <- Pico TX (UART1)	GP8
RYLR998	TX -> Pico RX (UART1)	GP9
Infrared operator remote	OUT (VS1838B)	GP5
Valve servo	PWM signal	GP14
Red VALVE FAULT LED	anode	GP16
Yellow COMMAND PENDING LED	anode	GP17
Green VALVE NOMINAL LED	anode	GP18
Emergency stop button	to ground	GP15
Onboard LED	heartbeat	GP25
Debug Probe / UART0 console	TX	GP0
Debug Probe / UART0 console	RX	GP1

Note: GPIO 2/3 are the classic I2C1 pins used throughout the Embedded Hacking breadboard; this project's map matches that board because it is the same board.

1602 LCD with I2C backpack

LCD backpack	Pico 2
VCC	3.3V
GND	GND
SDA	GP2
SCL	GP3

DHT11 process sensor

DHT11	Pico 2
VCC	3.3V
DATA	GP4
GND	GND

If your DHT11 has no onboard pull-up, add a 10K resistor between DATA and 3.3V. The firmware also enables the internal pull-up, but the external resistor makes reads far more reliable over jumper wires. The process is not nominal when the sensor fails or reads outside -5.0 C to 10.0 C.

Status LEDs

LED	Pico 2	Series resistor
Red (VALVE FAULT)	GP16 (anode)	220-330 Ohm to GND
Yellow (COMMAND PENDING)	GP17 (anode)	220-330 Ohm to GND
Green (VALVE NOMINAL)	GP18 (anode)	220-330 Ohm to GND

Exactly one lamp is lit at a time. Red is a valve fault or a failed-closed latch, yellow is a pending command or a moving valve, and green is a nominal line.

LED behavior

State	Lamp	Indication	Meaning
VALVE_OFF	none	All dark	Defined but never selected; the live state machine always drives fault, pending, or nominal.
VALVE_FAULT	Red	Solid	Valve fault, failed-closed latch, or the latched emergency stop.
VALVE_PENDING	Yellow	Solid	The valve is travelling after an accepted command.
VALVE_NOMINAL	Green	Solid	The valve is seated closed or fully open on a nominal line.

The three annunciator lamps are always solid; status_led.c never blinks them. Exactly one lamp is lit at a time, and VALVE_OFF leaves all three dark. A latched emergency stop forces VALVE_FAULT regardless of the valve state. The onboard GP25 LED is initialized as an output and driven as a heartbeat: monitor.c toggles it every four monitor ticks in monitor_heartbeat, so a running controller is visible even while idle.

Emergency stop button

Button	Pico 2
Leg 1	GP15
Leg 2	GND

The firmware enables the internal pull-up, so do not connect 3.3V to the button. This is the operator's hard stop: a press consumes one debounced edge, latches a fault, and forces the valve closed with priority over any remote command. Lab 4 explains how the priority is enforced and why it must be absolute.

SG90 valve servo

Servo	Pico 2
Signal (orange)	GP14
VCC (red)	5V (VBUS)
GND (brown)	GND

Solder the 1000uF capacitor across the servo 5V and GND rails to absorb the inrush current; without it the RP2350 can brown out when the valve moves. Seated (closed) is 0 degrees and open is 90 degrees.

Infrared receiver

VS1838B	Pico 2
OUT	GP5
VCC	3.3V
GND	GND

Point any NEC-compatible remote at the receiver. In Act III this is the operator remote, not a maintenance extra: the firmware decodes MONITOR_IR_OPEN (0x47), MONITOR_IR_CLOSE (0x45), and MONITOR_IR_ESTOP (0x46). There is no challenge and no secret on the optical surface, so the firmware applies the operator command directly; the fix track adds the missing authorization.

Using the remote

Point the NEC remote at the VS1838B receiver on GP5 and press a mapped button; the receiver idles high and pulls low on a mark. Every valid frame prints IR <NAME> (0xNN) on the console and is applied to the valve, unless the emergency stop is latched.

NEC command	Name	Action
0x47	MONITOR_IR_OPEN	Drives the valve to the open position (valve_apply_command(true, true)).
0x45	MONITOR_IR_CLOSE	Drives the valve to the closed position (valve_apply_command(false, true)).
0x46	MONITOR_IR_ESTOP	Latches the emergency stop and forces the valve closed with priority over later commands.

Once the emergency stop is latched, every further optical command is ignored until the controller is reset.

RYLR998 LoRa radio

The RYLR998 must be powered. Forgetting VDD is the single most common reason the link appears dead: the firmware prints while the radio sits silent.

RYLR998	Pico 2
VDD	3.3V
GND	GND
RXD	GP8 (Pico UART1 TX)
TXD	GP9 (Pico UART1 RX)

Attach the antenna before transmitting. TX and RX are crossed: the radio's RXD is the Pico's TX and vice versa.

Debug Probe (recommended)

Debug Probe	Pico 2
SWCLK	SWCLK (3-pin debug header)
SWDIO	SWDIO
GND	GND
UART TX	GP1 (Pico RX)
UART RX	GP0 (Pico TX)
GND	GND

The firmware enables stdio on both UART0 (115200) and USB, so you can watch boot output on the probe's console or on the Pico's own USB serial port. The Debug Probe is also the instrument for the Lab 3 malware work: it is how you watch the beacon, trigger the bomb, and step past the anti-debug trap.

Peripherals used

Every part in the Act III bill of materials is exercised by the firmware:

Peripheral	Role	Where it is used
Red, yellow, green LEDs	Tri-color SCADA valve annunciator	status_led.c drives exactly one lamp per state
Emergency stop button (GP15)	Operator hard stop	button.c consumes one debounced press in monitor_handle_estop
1602 I2C LCD	SCADA status and alarm readout	display.c renders the formatted lines over I2C1
DHT11 (GP4)	Process temperature and humidity	sensor.c reads the one-wire frame every telemetry interval
SG90 servo (GP14)	Valve actuator	servo.c drives the valve open and closed
1000uF capacitor	Bulk decoupling on the servo 5V rail	Required to keep the RP2350 from browning out on servo moves
VS1838B IR receiver (GP5)	Operator remote input	ir_remote.c captures and decodes the frame
NEC IR remote	Operator OPEN, CLOSE, and ESTOP	Sends 0x47, 0x45, and 0x46
RYLR998 (UART1)	LoRa command and status link	radio.c sends sealed frames and pumps inbound commands
Onboard GP25 LED	Onboard heartbeat	monitor.c toggles it every four monitor ticks in monitor_heartbeat
Debug Probe	SWD flashing, UART0 console, and malware analysis	stdio is enabled on both UART0 115200 and USB

Every Act III peripheral in the bill of materials is exercised by the firmware.

How the functionality works

Every input feeds the state machine in monitor_step, every output is driven once per tick, and the interactive console mirrors both over UART0 and USB. The DHT11 is sampled every two seconds, so one live status line appears about every two seconds. This is what each surface does at run time.

Inputs

Input	What it does when you use it
Infrared remote (GP5)	A decoded NEC frame prints IR <NAME> (0xNN) and is applied as an operator command, unless the emergency stop is latched.
Emergency stop button (GP15)	A debounced press prints BUTTON emergency stop -> valve fault, latches the fault, and forces the valve closed with priority over any remote command.
DHT11 (GP4)	The process sensor is sampled every tick; a good read prints a live status line, and a failed read prints SENSOR read failed -> WARNING.
RYLR998 (UART1)	Each inbound +RCV frame prints RX from 0xNNNN, N bytes and is offered to the sealed command path.

Outputs

Output	What it shows
Red, yellow, green LEDs	Exactly one solid lamp per state, red VALVE FAULT, yellow COMMAND PENDING or MOVING, green NOMINAL, and all three dark only in the unused OFF state; status_led.c never blinks them.
1602 I2C LCD	ST:<state> on the first line and PROC:<verdict> LNK:<state> on the second, refreshed every tick.
SG90 servo	The valve, seated closed at 0 degrees and open at 90 degrees, with the emergency stop forcing it closed.
Onboard GP25 LED	The heartbeat, toggled every four monitor ticks in monitor_heartbeat.

Watching the console

Open the UART0 console (Debug Probe) or the Pico's own USB serial port at 115200. The boot banner and control hint name the remote buttons and the push button:

=== OPERATION IRON VEIN // ACT III SCADA PIPELINE ===
REMOTE: CH+ 0x47 open | CH- 0x45 close | CH 0x46 estop
BUTTON: GP15 emergency stop

While the controller runs, a process read prints one live status line and each event prints a named line:

PROCESS t=23 h=610 ok=1 ST=CLOSED n=4
IR OPEN (0x47)
RX from 0x0001, 122 bytes
BUTTON emergency stop -> valve fault
SENSOR read failed -> WARNING

The status line carries the sensor value (t and h), the process verdict (ok), the annunciator state (ST), and a running status count (n). The event lines cover a decoded remote command, a button press, an inbound radio frame, and a failed sensor read.

Build and Flash

1. Install toolchain prerequisites

• Pico SDK 2.2.0+
• ARM GNU toolchain (arm-none-eabi)
• CMake and Ninja
• Python 3.x
• GDB (arm-none-eabi-gdb) for the Lab 3 malware analysis

Linux:

export PICO_SDK_PATH="$HOME/.pico-sdk/sdk/2.2.0"

macOS:

brew install cmake ninja arm-none-eabi-gcc python
export PICO_SDK_PATH="$HOME/.pico-sdk/sdk/2.2.0"

Windows: install PowerShell, Visual Studio Build Tools, CMake, Ninja, Python 3, and the ARM embedded toolchain.

2. Build the firmware

The clean firmware does not define SANDBOX_ONLY, so it ships no implant:

mkdir -p build && cmake -S . -B build -G Ninja -DPICO_BOARD=pico2 -DPICO_PLATFORM=rp2350-arm-s && cmake --build build

To build the malware-track image with the implant compiled in, turn the option on:

cmake -S . -B build-sandbox -G Ninja -DPICO_BOARD=pico2 -DPICO_PLATFORM=rp2350-arm-s -DSANDBOX_ONLY=ON && cmake --build build-sandbox

Build-time artifact guardrail:

• The build regenerates packet_artifact.h from scripts/packet_artifact.json before compiling.
• The build fails if the committed include/packet_artifact.h is stale relative to the JSON artifact.

Generated outputs:

• build/pipeline_valve_controller.elf (primary firmware binary)
• build/pipeline_valve_controller.uf2 (UF2 for BOOTSEL/picotool)
• build/pipeline_valve_controller_app.elf / .uf2 (backward-compatible copies)

3. Flash the RP2350

BOOTSEL (drag-and-drop): hold BOOTSEL while plugging in USB, then:

cp build/pipeline_valve_controller.uf2 /Volumes/RP2350/

picotool:

picotool load build/pipeline_valve_controller.uf2 -fx

(If picotool is not on your PATH, invoke it from $HOME/.pico-sdk/picotool/*/picotool/picotool.)

Debug Probe (SWD): with openocd installed you can flash and reset without touching BOOTSEL:

openocd -f interface/cmsis-dap.cfg -f target/rp2350.cfg \
  -c "program build/pipeline_valve_controller.elf verify reset exit"

4. Watch the console

Open the UART0 console (Debug Probe) or the Pico's USB serial port at 115200. On reset you should see:

BOOT
I2C scan:
  found 0x27
=== OPERATION IRON VEIN // ACT III SCADA PIPELINE ===
REMOTE: CH+ 0x47 open | CH- 0x45 close | CH 0x46 estop
BUTTON: GP15 emergency stop

found 0x27 confirms the LCD backpack answered on the I2C bus, and the banner confirms the controller reached its ready policy. If a peripheral fails, the firmware prints INIT FAIL and stops.

Lab 1: Bring-Up and Verify

Goal: prove the controller reads the process sensor, drives the LCD, takes an operator command, reaches the gateway, and moves the valve.

1. Wire the node per the pin map and attach the antenna.

2. Build and flash the clean firmware.

3. Connect the gateway radio to the laptop and find its port (/dev/cu.usbserial-* on macOS, /dev/ttyUSB* on Linux).

4. Start the SCADA gateway:

   python3 scripts/gateway.py --port /dev/cu.usbserial-XXXX --baud 115200
   

5. Press OPEN on the IR remote. The controller seals a request and the gateway prints it, then answers with a sealed valve command:

   +OK
   +OK
   +RCV=7,82,<82 hex characters>,-11,10
   VALVE seq=1 cmd=1
   

6. The controller turns yellow (COMMAND PENDING), receives the command, verifies the state tag and the anti-replay window, then turns green (VALVE NOMINAL) and drives the valve open. Press ESTOP at any time to latch a fault and close it.

Checkpoint: the LCD shows ST:OPEN and PROC:OK LNK:UP, the green LED is lit after the valve settles, and valve_log.csv gains one row per request:

utc,sender,auth,cmd,rssi_snr
2026-09-20T09:30:05+00:00,7,OK,1,"-11,10"

Theory check: why does a successful command prove the LCD initialized? Because monitor_init() only returns true when every peripheral, including the LCD, is ready; otherwise main prints INIT FAIL and never enters the loop.

Lab 2: Inspect the Wire Protocol

Goal: see the sealed envelope and the declared-length rule in action.

1. Capture a full +RCV line from the console or the gateway log.
2. Confirm the declared length equals the number of hex characters between the second comma and the RSSI field.
3. Split the hex into three parts: the first 48 hex characters are the 24-byte nonce, the last 32 are the 16-byte tag, and everything between is the ciphertext of the request or command body.
4. Locate the payload, its declared length, and the two tail fields in scripts/gateway.py (_rcv_parts and _split_payload), and explain why finding the first comma would be a bug.
5. Challenge: for the 21-byte command body, identify the four bytes of the sequence number, the one command byte, and the sixteen bytes of the state tag.

Checkpoint: you can explain why a frame must be sliced by the number in the declared length field, not by delimiter counting, and why the command byte is range-checked against the guarded open and close set before it can reach the actuator.

Lab 3: The Malware Track

Goal: find the FROSTLINE implant, prove what it does, and defuse it. This is the first act with a malware track, and this lab is its heart.

Safety: the implant is benign and confined to your breadboard. It beacons only to the local classroom hub, it actuates only your servo, and it writes only the reserved sector at 0x103FF000. There is no network, no filesystem, and no host impact.

Build the implant image

cmake -S . -B build-sandbox -G Ninja -DPICO_BOARD=pico2 -DPICO_PLATFORM=rp2350-arm-s -DSANDBOX_ONLY=ON && cmake --build build-sandbox

The clean build does not define SANDBOX_ONLY; the test build and the companion CTF build do. Compare the two binaries and explain why the implant symbols are absent from the clean one.

A: Find the beacon

1. Flash the SANDBOX_ONLY image and open the UART0 console.
2. Watch the radio, or break in implant_beacon under GDB, and capture the covert frame. It begins with the 4-byte magic DE AD BE EF.
3. Decode the 4-byte blob that follows: the low and high bytes of the tick counter, the marker byte 0xC7, and the debug-attached flag.
4. Explain why the beacon fires every 8 ticks and why it uses a magic preamble instead of a proper frame header.

The lesson: a beacon does not need to be loud to be found. It needs to be periodic.

B: Defuse the logic bomb

1. Locate the 8-byte arming magic FROSTLNE (IMPLANT_ARM_MAGIC) in the image.
2. Inject it and watch the implant arm. Without a probe attached, it detonates 3 ticks later by closing the valve on its own.
3. Trace the detonation in implant_detonate: it calls valve_close() directly, then latches the persistence marker.
4. Defuse it by neutralizing the arming path or the detonation call, and prove the valve no longer moves on the magic.

The lesson: the bomb does not touch the sealed protocol. It calls the actuator underneath it, which is why an authenticated wire is not an authenticated machine.

C: Defeat the anti-debug with GDB

This is the dynamic-analysis trap. The implant reads CoreDebug DHCSR at 0xE000EDF0; bit 0 is C_DEBUGEN and bit 1 is C_HALT. While a probe is attached, the implant suppresses both the beacon and the bomb.

1. Start the controller under the Debug Probe:

   arm-none-eabi-gdb build-sandbox/pipeline_valve_controller.elf
   (gdb) target extended-remote /dev/cu.usbmodemXXXX
   (gdb) monitor reset halt
   

2. Break in implant_tick and inspect implant_debug_attached. With a normal probe attached, it returns true, and the beacon and bomb stay silent.

3. Set a breakpoint after the anti-debug check, or clear the DHCSR debug bits in the debugger's view, and observe the beacon and the bomb resume.

4. Prove the payload: with the trap bypassed, the implant beacons and the logic bomb closes the valve.

The lesson: an anti-debug check is a branch, and every branch is a place to stand. The correct neutralization is not to babysit the branch; it is to remove the code.

D: The persistence preview

1. Trigger the bomb once and read the reserved sector at 0x103FF000.
2. Confirm the marker byte 0xC7 was written exactly once, and that a second trigger does not overwrite it.
3. Explain why a payload that writes a marker to flash is a preview of Act IV, where persistence is the whole lesson.

Malware-track checklist

• Locate the beacon magic and its interval.
• Identify the 8-byte arming magic and the 3-tick trigger delay.
• Read and explain the CoreDebug DHCSR anti-debug trap.
• Find the reserved-sector persistence marker and the write-once latch.
• Remove the code path, not just the branch, and confirm the clean build is implant-free.

Lab 4: The Fix Track

Goal: seal the controller so the red half and the implant cannot do to you what they did on the bench. Each control maps to a defect the earlier labs exposed.

1. Seal the valve command path

The old design accepted an unauthenticated valve angle. Act III replaces it with src/control.c: the request must open under the field key, the command byte must be in the guarded set (pt[4] > VALVE_COMMAND_OPEN is rejected), and the sequence and state tag must pass src/valve_auth.c before valve_apply_command is called. Re-run the Lab 3 forged-command injection: the tag fails and the valve does not move.

2. Emergency stop priority

The emergency stop is an operator safety control, and it must win over every remote command. monitor_service_inputs handles the ESTOP before it polls the remote or the radio, and monitor_apply_ir_command refuses to act while the latch is set. Re-run the lab: press ESTOP, then send a valid sealed OPEN. The valve stays closed and the fault lamp stays red until monitor_clear_estop() is called.

3. Fail closed

Loss of the gateway link, a fault, or a failed process reading must leave the valve closed. monitor_check_link calls valve_fail_closed when the link goes silent for VALVE_ESTOP_WAIT_MS, and valve_init seats the valve closed at boot. Re-run the link-loss test: pull the gateway and watch the valve seat and the fault latch.

4. Contain the implant

The implant is a build-time defect, so the fix is a build-time control:

• Do not define SANDBOX_ONLY in production. The clean build has no implant.
• Treat the firmware image as a signed artifact and verify it before flashing.
• At runtime, do not let any code path call the actuator directly; route every move through the guarded, authorized command path and record who authorized it.
• In production, burn the RP2350 secure-boot and debug-disable settings in OTP so SWD cannot read or write SRAM on a deployed controller.

The fix-track checklist

• Sealed command path: authenticate the frame, guard the command set, verify the sequence and the state tag.
• ESTOP priority: latch first, refuse remote commands while latched.
• Fail closed: seat the valve on boot, on link loss, and on every fault.
• Build integrity: no SANDBOX_ONLY in production, sign and verify images.
• Debug lockdown: OTP debug disable on the deployed part.
• Key lifecycle: provision the field key from OTP and rotate on a schedule.

Troubleshooting

Symptom	Likely cause	Fix
No BOOT on the console	Wrong console pins / not reset	Check UART0 GP0/GP1 or USB; press RESET
INIT FAIL with no 0x27 in the scan	LCD not answering	Check LCD VCC=3.3V, SDA=GP2, SCL=GP3, contrast pot
LCD shows blocks / nothing	Contrast or address	Turn the backpack contrast pot; confirm address 0x27 vs 0x3F
Process always BAD	DHT11 not reading	Check DATA=GP4; add 10K pull-up to 3.3V; wait 1-2 s after power-up
IR remote does nothing	Receiver wiring or remote protocol	Check OUT=GP5, VCC=3.3V; confirm the remote is NEC-compatible
Valve will not move on a remote command	Command guard or tag	Confirm the gateway holds the field key and the command byte is 0 or 1
AT+SEND sent but gateway sees nothing	Radio unpowered / wrong band	Power VDD, attach antenna, use matching band modules
Gateway sees nothing but +OK	Address/network mismatch	Confirm gateway radio provisioned to AT+ADDRESS=1, AT+NETWORKID=18
valve_log.csv stays empty while +RCV prints	Gateway parser regression	Ensure _split_payload checks the comma at the declared length
Command rejected on the controller	Tag, window, or command guard	Check the field key matches and the sequence is newer and in the guarded set
Valve closes by itself	Implant logic bomb (SANDBOX_ONLY build)	You are running the malware-track image; see Lab 3
Beacon data appears on the radio	Implant beacon (SANDBOX_ONLY build)	Expected in the malware-track build; see Lab 3
Debugger changes implant behavior	CoreDebug DHCSR anti-debug	The implant suppresses itself while a probe is attached; see Lab 3C

Testing Philosophy and Coverage

Hardware bugs are expensive to find on the bench, so the firmware is written so that almost all of it can be tested on the host. The suite compiles the real src/*.c files against mock Pico SDK headers (test/mock/), replacing GPIO, I2C, UART, and time with deterministic fakes, and it compiles src/implant.c with a host mock for the CoreDebug DHCSR register and the reserved flash sector.

• The mock GPIO can replay a recorded DHT11 waveform as an absolute time/level timeline, so the exact edge-timing decoder is exercised without a sensor.
• The mock I2C records every LCD byte, so rendered text can be decoded and asserted.
• The mock UART records outbound AT+SEND bytes and injects inbound +RCV lines, so the operator-to-gateway-to-valve path runs end to end with no radio.
• The implant host mock lets the tests set the DHCSR anti-debug bits and read the reserved-sector marker without touching real silicon.

Run the native test suite:

python3 scripts/run_tests.py

Or configure via CMake and CTest:

cmake -S test -B build-test -G Ninja && cmake --build build-test && ctest --test-dir build-test --output-on-failure

The suite has 132 cases and 409 checks with 0 failures, covering the full DHT11 waveform and every timeout shape, the valve state machine and its bounded travel, the sealed command path and its guards, the authorization window and state tag, the emergency-stop priority, fail-closed on link loss, the declared-length parser with hex-bearing payloads, the cryptographic primitives against published vectors, and the complete implant: beacon, logic bomb, anti-debug, and write-once persistence.

Verify 100% line coverage of owned firmware modules:

python3 scripts/check_coverage.py

The coverage report shows 1982 / 1982 lines, 100.00%. main.c is excluded from coverage by design. The Python adapter suite (test/test_field_crypto.py and test/test_pipeline_valve.py) adds 17 more tests, including the RFC 9106 Argon2id known-answer test.

The harness itself is a small in-repo framework (test/harness/) so the repo vendors no third-party code and every owned file obeys the coding standard.

Generating Packet Artifacts

scripts/gen_packet.py writes the build-time generated header from the JSON artifact:

• scripts/packet_artifact.json is the source of truth.
• include/packet_artifact.h is the generated header, committed for the build guardrail.

Why these constants are compiled into firmware:

• The RP2350 firmware has no runtime JSON parser or filesystem on this path.
• include/packet_artifact.h is generated from the JSON so the frame size, node id, gateway address, wait time, servo pulses, DHT timeout, and provisioning constants are embedded in flash.
• This is provisioned data; regenerate whenever you rotate node identity, gateway addressing, or key material.

To sync the committed header from the JSON artifact:

python3 scripts/gen_packet.py --from-json scripts/packet_artifact.json --header-out include/packet_artifact.h

The check_packet_artifact_header CMake target fails the build when the committed header is stale.

Code Standards

This repository enforces unusually strict standards because the point is to teach disciplined embedded and tooling practice, not just working code.

C standard

• Every function body has no blank lines.
• Every function body is at most eight lines (Doxygen comment blocks and lone braces excluded).
• Every file, function, macro, type, and struct member carries Doxygen @brief documentation.
• Naming: snake_case files/functions, UPPER_SNAKE macros, snake_case_t types.

Run the C audit:

python3 scripts/audit_c_standard.py

Python standard

• Strict PEP8, four-space indents, snake_case, 79-character lines.
• Every function has a NumPy-style docstring.
• Every function executable body is at most eight lines, with no exceptions.
• No blank lines inside function bodies.

Run the Python audit:

python3 scripts/audit_python_standard.py

Both audits must report nothing.

Project Layout

• src/main.c: firmware entry point
• src/monitor.c: state machine tying the operator remote, sealed command path, valve, ESTOP, process sensor, and radio together
• src/implant.c: SANDBOX_ONLY FROSTLINE implant (beacon, logic bomb, anti-debug, persistence preview)
• src/valve.c: valve state machine and fail-closed policy
• src/control.c: sealed valve command path with a guarded command set
• src/valve_auth.c: authorization record, monotonic anti-replay window, authenticated state tag
• src/sensor.c: DHT11 one-wire sampling and process-band classifier
• src/display.c: 1602 LCD rendering over the PCF8574 I2C backpack
• src/radio.c: RYLR998 provisioning, AT-command interface, and +RCV parser
• src/status_led.c: red/yellow/green VALVE FAULT / COMMAND PENDING / VALVE NOMINAL annunciator
• src/button.c: debounced emergency-stop input
• src/servo.c: 50 Hz PWM valve actuator
• src/ir_remote.c: VS1838B edge timing and NEC operator remote decoder
• src/crc.c: CRC-16/CCITT-FALSE helper
• src/chacha20.c, src/poly1305.c, src/crypto_aead.c, src/blake2b.c, src/argon2.c, src/crypto_kdf.c, src/envelope.c: the in-repo cryptographic stack
• include/pipeline_valve.h: board-level pin, provisioning, and implant configuration
• include/implant.h, include/control.h, include/valve_auth.h, include/valve.h: implant, command, authorization, and valve interfaces
• include/field_secrets.h: lab-only committed key material
• include/packet_artifact.h: generated packet artifact header
• test/test_pipeline_valve_and_security.c, test/test_peripheral_and_crypto.c: comprehensive test suites
• test/mock/: Pico SDK hardware mocks plus the implant CoreDebug and reserved-flash host mock
• test/harness/: minimal in-repo test harness (strictly C-standard compliant)
• scripts/gateway.py: SCADA gateway with radio provisioning, authentication, CSV logging, and sealed command replies
• scripts/spoof.py: forged and replayed command injection client
• scripts/sim_edge.py: laptop valve-node simulator
• scripts/field_crypto.py: pure-Python interoperable crypto
• scripts/gen_packet.py / scripts/packet_artifact.json: packet artifact generator and source
• scripts/run_tests.py, scripts/check_coverage.py: test runner and coverage report
• scripts/audit_c_standard.py, scripts/audit_python_standard.py: code-standard auditors
• scripts/gen_banner.py: banner generator
• paper.typ / paper.pdf: classroom paper describing the protocol, the implant, and the exercise
• .github/workflows/release.yml: tag-driven UF2 release workflow

Glossary

• AEAD: authenticated encryption with associated data; one operation for secrecy and integrity.
• Anti-debug: a check that detects an attached debugger and changes behavior. Here it reads CoreDebug DHCSR at 0xE000EDF0 (bits C_DEBUGEN and C_HALT).
• Anti-replay window: a monotonic sequence rule that rejects a valid frame that has already been used.
• Argon2id: the memory-hard password hash (RFC 9106) used to derive the field key.
• AT command: a short ASCII command (AT+...) understood by the radio.
• Beacon: a periodic covert transmission, here the DE AD BE EF frame the implant emits every 8 ticks.
• CRC: cyclic redundancy check, a checksum for detecting corruption.
• Declared length: the byte count the sender claims for a payload; the receiver slices exactly that many characters.
• DHT11: a low-cost temperature/humidity sensor using a custom one-wire protocol, used here as the process sensor.
• ESTOP: the emergency stop. A latched, highest-priority input that forces the valve closed.
• Fail closed: a fault leaves the valve seated closed, the safe line state.
• Field key: the key that seals frames on the wire and computes the state tag.
• HD44780: the character-LCD controller inside a 1602 module.
• I2C: a two-wire bus (SDA/SCL) used here for the LCD backpack.
• Implant: code that runs on the device but is not part of its intended function. Here the SANDBOX_ONLY FROSTLINE module.
• Logic bomb: a payload that arms on a trigger and acts later. Here it arms on the 8-byte magic FROSTLNE and closes the valve 3 ticks later.
• LoRa: a long-range, low-power sub-GHz radio modulation.
• NEC: the infrared remote encoding the VS1838B decodes.
• PCF8574: an I2C I/O expander that drives the LCD's parallel interface.
• Persistence: surviving a removal attempt. The implant previews it with a write-once marker in the reserved sector 0x103FF000.
• RSSI / SNR: received signal strength and signal-to-noise ratio reported with each +RCV frame.
• SANDBOX_ONLY: the build guard that compiles the benign implant. The clean firmware does not define it.
• SCADA: supervisory control and data acquisition; the industrial control context for this act.
• State tag: a keyed tag over the authorization record that detects a tampered verdict.
• UART: a serial port used to talk to the radio.
• XChaCha20-Poly1305: the AEAD used for every sealed frame, with a 192-bit nonce and a 128-bit tag.

Further Reading

• Act I, the sensor and telemetry chapter: https://github.com/mytechnotalent/cold-chain-monitor
• Act II, the access gate chapter: https://github.com/mytechnotalent/access-gate
• The companion CTF for this act: https://github.com/mytechnotalent/CTF_pipeline-valve-controller
• Embedded Hacking course and breadboard: https://github.com/mytechnotalent/Embedded-Hacking
• Reverse Engineering self-study course: https://github.com/mytechnotalent/Reverse-Engineering
• paper.typ / paper.pdf: the classroom paper for this project.
• DHT11 datasheet, RYLR998 AT command reference, SG90 datasheet, and VS1838B datasheet (module vendors).

Next

OPERATION IRON VEIN CTF

License

MIT License