Introduction

If your private key exists on a computer connected to the Internet, it is Public. It is only a matter of time before a 0-day exploits your OS, your browser, or your Wi-Fi driver.

True security requires Physics: Disconnecting the wires. Removing the Bluetooth antenna. Sealing the device in a Faraday Cage. This lesson explores the paranoia needed to secure $1 Billion.

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The Physics: Air Gaps & Data Diode

An Air Gap is a physical separation between the Secure Network and the Insecure Network (Internet). But Air Gaps can be jumped via:

1. USB: BadUSB firmware attacks (Stuxnet).
2. Sound: Ultrasonic beacons.
3. Light: Blink codes from LEDs.

The Physics: The only secure channel is a Data Diode. QR Codes are optical data diodes. Scanner -> Screen. The Screen cannot infect the Scanner (Physics determines flow). SD Cards are not diodes, but they have a simpler attack surface than USB.

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Deep Dive: PSBT (Partially Signed Bitcoin Transactions)

How do you sign a transaction without the key touching the internet? PSBT (BIP174).

The Workflow:

1. Online PC: Creates an Unsigned Transaction. Saves to SD Card.
2. Sneakernet: Human walks SD Card to the Vault.
3. Offline Device: Reads SD Card. User verifies address on screen. Signs. Saves Signed Tx to SD Card.
4. Sneakernet: Human walks SD Card back to Online PC.
5. Online PC: Broadcasts Signed Tx.

Physics: The Offline Device never calculates network packets. It only calculates Elliptic Curve Math. It has no TCP/IP stack to exploit.

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Strategy: Side Channel Defense (Simonis Attacks)

Even if Air-Gapped, physics betrays you. Power Analysis: The power consumption of the CPU leaks the Private Key bits. Acoustic Analysis: The coil whine of the capacitors changes based on the computation.

Defense:

1. Faraday Cage: Blocks EM radiation (Radio/Wi-Fi/Bluetooth).
2. Sound Isolation: Heavy safe walls.
3. Power Conditioning: Battery power only (No AC mains connection).

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Code: Glacier Protocol (Ceremony)

The Glacier Protocol is the gold standard for high-security storage.

# Simplified Ceremony Script
def generate_keys_offline():
    # 1. Boot from Tails OS (Live USB)
    # 2. Remove Network Cards physically
    # 3. Roll Dice (Entropy) -> 128 rolls
    entropy = "10110101..."

    # 4. Generate Shares (Shamir's Secret Sharing)
    # 3-of-5 setup
    shares = shamir.split(entropy, 3, 5)

    # 5. Print Shares to Paper
    # No Printer Memory (Use Dumb Printer)
    for share in shares:
        print_to_paper(share)

    # 6. Destroy RAM (Power Cycle)
    # 7. Destroy Hardware (Literally smash the laptop)

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Practice Exercises

Exercise 1: The Evil Maid (Beginner)

Scenario: You leave your Ledger in your hotel room safe. Attack: Maid opens safe, replaces Ledger with modified firmware version. Defense: Tamper-evident bags (Glitter nail polish on screws).

Exercise 2: QR Code Injection (Intermediate)

Scenario: The Watch-Only wallet generates a malicious QR code that exploits a buffer overflow in the Hardware Wallet’s camera driver. Result: Code execution on the Cold Device. Lesson: Even QR codes are attack vectors.

Exercise 3: 5 Wrench Attack (Advanced)

Scenario: An attacker threatens physical violence. All crypto defense fails against physical coercion. Defense: Duress Wallet. A secondary PIN that unlocks a small “decoy” balance, while alerting police or wiping the main keys.

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Knowledge Check

1. Why is USB considered “Broken”?
2. What is a Data Diode?
3. Why use Dice for entropy?
4. What is a Side Channel attack?
5. What is a Duress PIN?

Answers

1. Controller Firmware. USB keys can emulate keyboards/network cards to hack the host.
2. One-way flow. Information can flow A->B but never B->A (e.g., Screen reading a QR).
3. Physics. Computers are deterministic; gravity is chaotic. Dice are true random.
4. Leakage. Inferring secrets from indirect signals (Power, Sound, Radiation).
5. Plausible Deniability. A password that unlocks a fake wallet under coercion.

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Summary

• Air-Gap: Physical disconnection.
• PSBT: Offline signing standard.
• Entropy: Requires physical chaos.

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