tinygo-firmware

Skycoin Hardware Wallet - TinyGo Firmware

This is a TinyGo implementation of the Skycoin hardware wallet firmware for the STM32F205RG microcontroller. It provides the same functionality as the C firmware but written entirely in Go.

Features

• BIP39 mnemonic generation and validation (12/24 words)
• Skycoin address derivation using deterministic key generation
• ECDSA message signing (secp256k1)
• Transaction signing
• PIN protection
• OLED display (SSD1306, 128x64)
• USB HID communication

Requirements

TinyGo

Install TinyGo 0.30.0 or later:

# On Linux (Ubuntu/Debian)
wget https://github.com/tinygo-org/tinygo/releases/download/v0.30.0/tinygo_0.30.0_amd64.deb
sudo dpkg -i tinygo_0.30.0_amd64.deb

# on Arch Linux (btw)
yay -S tinygo-bin

# On macOS
brew tap tinygo-org/tools
brew install tinygo

ARM Toolchain

The ARM toolchain is needed for linking:

# On Linux (Ubuntu/Debian)
sudo apt-get install gcc-arm-none-eabi

# on Arch Linux (btw)
sudo pacman -S tinygo-bin gcc-arm-none-eabi


# On macOS
brew tap ArmMbed/homebrew-formulae
brew install arm-none-eabi-gcc

USB Rules (Linux)

Create /etc/udev/rules.d/99-skywallet.rules:

# Skycoin Hardware Wallet
SUBSYSTEM=="usb", ATTR{idVendor}=="313a", ATTR{idProduct}=="0001", MODE="0666"
KERNEL=="hidraw*", ATTRS{idVendor}=="313a", ATTRS{idProduct}=="0001", MODE="0666"

Then reload rules:

sudo udevadm control --reload-rules
sudo udevadm trigger

Building

Release Build

make build

This creates skyfirmware-tinygo.bin (approximately 71KB).

Debug Build

make build-debug

Debug builds include additional debug screens for development.

Clean

make clean

Flashing

Via Hardware Wallet Daemon

If the device already has a bootloader installed:

curl -X PUT http://127.0.0.1:9510/api/v1/firmware_update \
  -F "file=@skyfirmware-tinygo.bin"

Via ST-LINK

For a fresh device or to flash with bootloader:

# Check device is detected
st-info --probe

# Flash full firmware (bootloader + firmware)
st-flash write full-firmware.bin 0x08000000

Communication

Use the skyhw CLI tool (integrated into the skycoin repository):

# Get device features
skyhw cli features

# Ping the device
skyhw cli ping "hello"

# Generate addresses
skyhw cli addressGen --addressN 5

# Sign a message
skyhw cli signMessage --message "test message" --addressN 0

Supported Messages

Message	Description
Initialize	Start session, get Features
GetFeatures	Get device information
Ping	Echo test, supports TEST: commands
Wipe	Factory reset device
GenerateMnemonic	Create new 12/24 word mnemonic
RecoveryDevice	Restore from existing mnemonic
LoadDevice	Load mnemonic directly (debug)
SetMnemonic	Set mnemonic with validation
ChangePin	Set or change PIN
SkycoinAddress	Generate Skycoin addresses
SkycoinSignMessage	Sign message with private key
TransactionSign	Sign Skycoin transaction
GetRawEntropy	Get random bytes
GetMixedEntropy	Get entropy mixed with host
ApplySettings	Set device label/language
Backup	Display mnemonic for backup
Cancel	Cancel current operation

USB Protocol

• VID: 0x313A, PID: 0x0001
• HID device with 64-byte vendor-defined reports
• Message format: ?## + msg_id (2B) + length (4B) + protobuf payload
• Multi-packet messages supported (continuation starts with ?)

Architecture

tinygo-firmware/
├── main.go              # Entry point, main loop
├── usb_device.go        # USB HID state machine
├── usb_descriptors.go   # USB descriptors
├── messages.go          # Message framing protocol
├── protobuf.go          # Protobuf encoding/decoding
├── handlers.go          # Message handlers
├── dispatch.go          # Message dispatcher
├── storage.go           # Flash storage
├── oled.go              # OLED display driver
├── buttons.go           # Button handling, UI layouts
├── bip39.go             # BIP39 mnemonic implementation
├── bip39_words.go       # BIP39 wordlist
├── keygen.go            # Key derivation
├── ecdsa.go             # ECDSA signing
├── secp256k1.go         # secp256k1 field/point math
├── sha256.go            # SHA256 implementation
├── ripemd160.go         # RIPEMD160 implementation
├── base58.go            # Base58 encoding
├── transaction.go       # Transaction signing
├── recovery.go          # Device recovery flow
├── debug_on.go          # Debug mode (build tag)
├── debug_off.go         # Release mode (build tag)
├── stm32f205.json       # TinyGo target definition
├── stm32f205-firmware.ld # Linker script
├── device_stm32f205.s   # Startup assembly
└── Makefile             # Build system

Development

See DEVELOPMENT.md for detailed development guidelines, including:

• TinyGo bare-metal memory constraints
• String handling issues with gc=leaking
• Fixed buffer patterns
• Protobuf encoding patterns
• Test commands via ping

Quick Test Commands

# Test SHA256 implementation
skyhw cli ping "TEST:SHA256"

# Test address generation
skyhw cli ping "TEST:ADDR"

# Test mnemonic validation
skyhw cli ping "TEST:VMNEM"

# Test ECDSA public key generation
skyhw cli ping "TEST:PUBKEY1"

See DEVELOPMENT.md for the complete list of TEST: commands.

Memory Constraints

The firmware runs with:

• -gc=leaking - No garbage collection
• -scheduler=none - No goroutine scheduler
• -opt=z - Size optimization

All memory is statically allocated using fixed-size buffers. Dynamic allocation (make, append) is avoided to prevent memory corruption.

Firmware Size

Current binary size: ~71KB (signed)