Hardware Overview

Documentation Index

Fetch the complete documentation index at: https://docs.zerokeyusb.com/llms.txt

Use this file to discover all available pages before exploring further.

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Built for trust

ZeroKeyUSB is a self-contained, hardware-based password manager.
Engineered with a single goal: protect your credentials without ever connecting to the Internet. Each unit is assembled, tested, and encapsulated in industrial-grade epoxy resin to prevent external tampering — making it waterproof, dust-proof, and maintenance-free.

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System architecture

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Component list

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Why these components

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🧠 SAMD21E18A microcontroller

The ARM Cortex-M0+ processor balances performance, size, and power efficiency:

• 256 KB Flash — room for firmware, fonts, 9 keyboard layouts, and PROGMEM icon bitmaps.
• 32 KB SRAM — enough for display buffer, credential cache, and TOTP workspace without dynamic allocation.
• Native USB — hardware USB Full-Speed peripheral eliminates the need for external USB bridge chips.
• Hardware DSU — Data Scrambling Unit provides hardware CRC32 for fast boot-time firmware integrity checks.
• BOOTPROT fuse — BOOTPROT=7 locks the first 16 KB of Flash, preventing application code from modifying the bootloader.

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🔐 ATECC608A secure element

The ATECC608A provides three capabilities that software alone cannot guarantee:

The MAHDA-T SKU has hardware AES disabled at factory, so encryption runs in software on the MCU. The ATECC is still critical for entropy, identity, and rate-limiting.

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💾 M24C64-WMN6TP EEPROM

• 8 KB of non-volatile storage organized in 32-byte pages.
• >1 million write cycles per page — decades of normal use.
• All credential data is AES-128 CBC encrypted before writing — the I²C bus only sees ciphertext.
• Page boundary awareness: the firmware splits writes that cross 32-byte page boundaries to avoid the M24C64’s address wrap-around behavior.

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🖐️ TS06 touch controller

• Sealed, six-channel capacitive touch IC (five channels actively used).
• Internal baseline calibration — no analog tuning required.
• Minimum sensitivity (0x3F) set at boot to prevent false triggers through the epoxy encapsulation.
• 80 ms debounce, 800 ms long-press threshold, 150 ms channel lockout — all handled in firmware.

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💡 SSD1306 OLED

• 128×32 pixels, white-on-black, high contrast.
• Driven via I²C at address 0x3C.
• Full-frame refresh (~512 bytes per frame) through Adafruit_SSD1306 library.
• Excellent visibility in both daylight and darkness.
• Protected behind the sealed epoxy window.

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⚡ USB-C connection

• Draws approximately 20 mA — similar to a wireless mouse.
• No battery — fully powered from the host USB port.
• No wireless — no Wi-Fi, Bluetooth, or NFC hardware exists on the PCB.
• Works with Windows, macOS, Linux, Android, and iPadOS.

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I²C bus

All peripherals share a single I²C bus at 100 kHz: SDA and SCL are on PA08 and PA09 respectively. External pull-up resistors are present on the PCB.

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Physical design

• Encapsulated in epoxy resin — prevents corrosion, dust, moisture ingress, and physical tampering.
• No wireless interfaces — eliminates remote attack surfaces entirely.
• No external screws or seams — the device cannot be non-destructively opened.
• Gold-plated touch pads — durable, corrosion-resistant, and visible through the resin.

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Transparency, not exposure

ZeroKeyUSB is fully open source. The firmware and hardware schematics are publicly available on
GitHub → Depbit-lab/zerokeyusb.
Anyone can verify exactly what code runs on their device. Firmware updates require physical access — either via SWD pogo pins or the USB bootloader with signed firmware. There is no remote update mechanism.