By @RogueOps | Proudly built for the Ethical Hackers Den Community

If you are a sysadmin, network engineer, or ethical hacker, you know the dream: having a reliable, pocket-sized terminal that you can pull out anywhere to manage remote servers, triage infrastructure, or run field diagnostics—without lugging around a heavy laptop.

Enter the M5Stack Cardputer ADV. Powered by an ESP32-S3, this credit-card-sized device has all the hardware needed for serious field work. But standard firmware often falls short, suffering from frozen terminal screens, awkward keyboard layouts, and crashes during complex encryption handshakes.

That is why we built RogueSSH—a high-performance, scrollable SSH client firmware engineered specifically for the field. Today, we are breaking down what makes RogueSSH a game-changer, looking under the hood at the C++ code, and showing you how to get it running.

Why RogueSSH Outperforms Standard Firmware

When you are working on a 240x135 pixel screen with a miniature 56-key keyboard, standard terminal adaptations fail. RogueSSH was designed from the ground up to solve the three biggest bottlenecks of micro-computing: navigation, memory management, and key mapping.

Core Field-Ready Features:

• Persistent Credentials: Stores Wi-Fi and SSH settings securely in ESP32 Non-Volatile Storage (NVS). Say goodbye to hardcoding sensitive passwords in your Arduino sketch!
• Native VT100 Navigation: Seamlessly interact with your remote server's bash history and cursor movement using intuitive ALT key combinations.
• True ASCII Compatibility: Full support for Backspace/Delete (ASCII 127) and Carriage Return transmission for a true Linux terminal feel.

Under the Hood: How RogueSSH Works (Code Breakdown)

Let’s look at the educational engineering behind RogueSSH. How do you solve complex hardware limitations using C++ on an ESP32-S3? Here are three fundamental design patterns we used.

1. Bypassing Mini-Keyboard Bottlenecks (The "Nano" Fix)

One of the most frustrating things about embedded keyboards is trying to use command-line editors like nano. Normally, pressing Ctrl + O (Save) or Ctrl + X (Exit) fails because the hardware loop sends the printable characters "o" or "x" instead of the Control modifier.

In Linux, control characters are simply standard ASCII bytes: Ctrl+A is ASCII 1, and Ctrl+Z is ASCII 26. Therefore, Ctrl+O is simply decimal 15 (0x0F), and Ctrl+X is decimal 24 (0x18). In RogueSSH, we mapped these directly to the FN layer:

// Injecting raw ASCII Control Bytes via the FN layer
if (fn_pressed) {
    // Save file in nano (Ctrl + O -> ASCII 15)
    if (M5Cardputer.Keyboard.isKeyPressed('o')) { 
        char ctrl_o = 15; 
        ssh.write(&ctrl_o, 1); 
        return; 
    }
    // Exit nano (Ctrl + X -> ASCII 24)
    if (M5Cardputer.Keyboard.isKeyPressed('x')) { 
        char ctrl_x = 24; 
        ssh.write(&ctrl_x, 1); 
        return; 
    }
    // Search in nano (Ctrl + W -> ASCII 23)
    if (M5Cardputer.Keyboard.isKeyPressed('w')) { 
        char ctrl_w = 23; 
        ssh.write(&ctrl_w, 1); 
        return; 
    }
}

2. Rock-Solid Cryptographic Stability with FreeRTOS

SSH handshakes require heavy cryptographic math (like Diffie-Hellman key exchange). Running this in a standard Arduino loop() will quickly trigger the ESP32's Watchdog Timer (WDT), causing the device to randomly reboot.

To guarantee zero crashes, RogueSSH isolates the entire SSH connection and terminal rendering into a dedicated, high-priority FreeRTOS task allocated with a massive 48KB stack size:

void setup() {
    auto cfg = M5.config();
    M5Cardputer.begin(cfg);
    
    // Initialize NVS Preferences
    prefs.begin("ssh_cfg", true); 
    
    // Pin SSH task to Core 1 with 48,152 bytes of stack memory
    xTaskCreatePinnedToCore(
        sshMainTask,    // Task function
        "sshMainTask",  // Name of task
        49152,          // Stack size in words (48KB+)
        NULL,           // Task input parameter
        1,              // Priority
        NULL,           // Task handle
        1               // Core ID
    );
}

3. Universal Case-Insensitive Control Shifting

What if you want to use a control key we didn't explicitly map to the FN key, such as Ctrl + C to kill a script or Ctrl + L to clear the screen? RogueSSH includes a bitwise translation algorithm that intercepts alphabetical keys while the physical CTRL button is held and mathematically shifts them down to the ASCII 1–26 range:

Keyboard_Class::KeysState status = M5Cardputer.Keyboard.keysState();

if (status.word.size() > 0) {
    for (auto c : status.word) {
        // Check if CTRL is pressed alongside any letter (a-z)
        if (ctrl_pressed && (c >= 'a' && c <= 'z')) {
            // Shift ASCII value: 'a' (97) - 'a' + 1 = ASCII 1 (Ctrl+A)
            char ctrl_byte = (c - 'a' + 1); 
            ssh.write(&ctrl_byte, 1);
        } else {
            // Transmit normal typed character
            ssh.write(&c, 1);
        }
    }
}

Quick Reference: RogueSSH Keyboard Controls

Once you flash the firmware onto your M5Cardputer ADV, master these shortcuts to navigate your terminal with lightning speed:

Ready to upgrade your EDC (Every Day Carry)? Grab your M5Cardputer, flash RogueSSH, and take control of your infrastructure from anywhere.