BitspendPayment · aruokhai · Apr 11, 2026 · Apr 1, 2026 · Apr 10, 2026 · Apr 10, 2026
diff --git a/.gitignore b/.gitignore
@@ -23,16 +23,20 @@
 **/.venv/
 **/__pycache__/
 
-# Pico firmware
-*/pico-signer.elf
-*/pico-signer.uf2
+# HW Signer firmware build artifacts
+*.elf
+*.uf2
+*.bak
+hwsigner-secure/target/
+embassy-rp-fork/target/
 threshold/target
 threshold-ffi/target
 cosigner/target
 server/target
 e2e/signer-server/target
 ark/target
 ark-ffi/target
+hwsigner-secure/target
 
 # IDE
 .vscode/

diff --git a/Makefile b/Makefile
@@ -6,21 +6,24 @@
 #    make e2e-ark        Run Ark E2E test
 #    make hardware       Start regtest for hardware device (no Ark)
 #    make hardware-ark   Start regtest for hardware device with Ark
-#    make flash          Build & flash Pico 2 firmware (UF2)
+#    make hw-build       Build HW Signer TrustZone firmware (Secure + NS)
+#    make hw-flash       Flash HW Signer via debug probe
+#    make hw-test        Smoke test HW Signer over USB HID
 #    make down           Stop everything
 # ═══════════════════════════════════════════════════════════════════════════════
 
-.PHONY: e2e e2e-ark hardware hardware-ark flash down \
+.PHONY: e2e e2e-ark hardware hardware-ark down \
 	ffi-build ffi-android threshold-ffi-build threshold-ffi-android ark-ffi-build ark-ffi-android \
-	cosigner-build server-build signer-build pico-build \
+	cosigner-build server-build signer-build \
+	hw-build hw-build-secure hw-build-ns hw-flash hw-flash-probe hw-test \
 	regtest-up regtest-down bitcoin-init mine-loop adb-reverse \
 	signer-run signer-stop server-run server-stop \
 	arkd-up arkd-down arkd-init \
-	proto threshold-test threshold-ffi-test pico-flash-probe pico-test \
+	proto threshold-test threshold-ffi-test \
 	flutter flutter-run ark-newaddress crypto-bench \
 	stress-test load-test \
 	signet-hardware-ark signet-down e2e-mutinynet e2e-mutinynet-ark \
-	e2e-test e2e-ark-test regtest regtest-ark regtest-hardware regtest-hardware-ark regtest-hardware-ark-down pico-flash
+	e2e-test e2e-ark-test regtest regtest-ark regtest-hardware regtest-hardware-ark regtest-hardware-ark-down
 
 # ── Variables ─────────────────────────────────────────────────────────────────
 
@@ -96,24 +99,7 @@ hardware-ark: cosigner-build server-build ffi-build ffi-android
 		--wasm ../cosigner/target/wasm32-wasip1/release/cosigner.wasm \
 		--port 50051
 
-# 5) Build and flash Pico 2 firmware via UF2 (hold BOOTSEL + plug in USB first)
-flash: pico-build
-	@echo "Converting ELF to UF2..."
-	cp pico-signer/target/thumbv8m.main-none-eabihf/release/pico-signer pico-signer/pico-signer.elf
-	picotool uf2 convert pico-signer/pico-signer.elf pico-signer/pico-signer.uf2 --family rp2350-arm-s
-	@echo ""
-	@echo "==> Created pico-signer/pico-signer.uf2"
-	@echo "==> Copy to the RP2350 drive:  cp pico-signer/pico-signer.uf2 /media/$$USER/RP2350/"
-	@echo ""
-	@if [ -d "/media/$$USER/RP2350" ]; then \
-		cp pico-signer/pico-signer.uf2 /media/$$USER/RP2350/ && \
-		echo "Copied! Pico will reboot with new firmware."; \
-	else \
-		echo "RP2350 drive not found. Hold BOOTSEL + plug in the Pico, then run:"; \
-		echo "  cp pico-signer/pico-signer.uf2 /media/$$USER/RP2350/"; \
-	fi
-
-# Stop everything (server, signer, mine loop, Docker)
+# 5) Stop everything (server, signer, mine loop, Docker)
 down:
 	@echo "Stopping all services..."
 	-pkill -f "target/release/server" || true
@@ -125,6 +111,38 @@ down:
 	sudo rm -rf $(DATA_DIR) 2>/dev/null || true
 	@echo "All stopped."
 
+# ═══════════════════════════════════════════════════════════════════════════════
+#  HW SIGNER (TrustZone — Secure + Non-Secure worlds)
+# ═══════════════════════════════════════════════════════════════════════════════
+
+# Build Secure world (rp235x-hal, crypto, SAU — generates target/veneers.o)
+hw-build-secure:
+	@echo "Building HW Signer Secure world..."
+	cd hwsigner-secure && cargo +nightly build --release
+
+# Build Non-Secure world (Embassy, USB HID — links veneers.o from Secure build)
+hw-build-ns: hw-build-secure
+	@echo "Building HW Signer Non-Secure world..."
+	cd hwsigner && cargo clean && cargo +nightly build --release
+
+# Build both worlds
+hw-build: hw-build-ns
+
+# Flash both worlds via debug probe (requires SWD probe connected)
+hw-flash: hw-build
+	@echo "Flashing via debug probe..."
+	cp hwsigner-secure/target/thumbv8m.main-none-eabihf/release/hwsigner-secure hwsigner-secure/hwsigner-secure.elf
+	cp hwsigner/target/thumbv8m.main-none-eabihf/release/hwsigner hwsigner/hwsigner.elf
+	probe-rs download --chip RP2350 hwsigner-secure/hwsigner-secure.elf
+	probe-rs download --chip RP2350 hwsigner/hwsigner.elf
+	probe-rs reset --chip RP2350
+	@echo "Flashed and reset!"
+
+# Smoke test HW Signer over USB HID (no phone needed)
+hw-test:
+	@echo "Testing HW Signer over USB HID..."
+	scripts/.venv/bin/python3 scripts/test_hwsigner.py $(ARGS)
+
 # ═══════════════════════════════════════════════════════════════════════════════
 #  BUILD TARGETS
 # ═══════════════════════════════════════════════════════════════════════════════
@@ -178,10 +196,6 @@ signer-build:
 	-sudo chown -R $(USER):$(USER) e2e/signer-server/target 2>/dev/null || true
 	cd e2e/signer-server && cargo build --release
 
-pico-build:
-	@echo "Building Pico Signer firmware..."
-	cd pico-signer && cargo build --release
-
 # ═══════════════════════════════════════════════════════════════════════════════
 #  INFRASTRUCTURE
 # ═══════════════════════════════════════════════════════════════════════════════
@@ -268,14 +282,6 @@ threshold-ffi-test:
 	@echo "Running threshold-ffi tests..."
 	cd threshold-ffi && cargo test
 
-pico-flash-probe: pico-build
-	@echo "Flashing via debug probe..."
-	cd pico-signer && cargo run --release
-
-pico-test:
-	@echo "Testing Pico Signer over USB HID..."
-	scripts/.venv/bin/python3 scripts/test_pico.py $(ARGS)
-
 flutter: ffi-android
 	cd ap && flutter run
 
@@ -354,4 +360,3 @@ regtest-down: down
 regtest-hardware: hardware
 regtest-hardware-ark: hardware-ark
 regtest-hardware-ark-down: down
-pico-flash: flash
diff --git a/README.md b/README.md
@@ -1,6 +1,6 @@
 # Merlin Wallet
 
-A **self-custodial Bitcoin wallet** powered by **FROST threshold signatures** and a **Raspberry Pi Pico 2 hardware signer**. No single device ever holds the full private key.
+A **self-custodial Bitcoin wallet** powered by **FROST threshold signatures** and an **RP2350 hardware signer**. No single device ever holds the full private key.
 
 Three independent identities — your phone, a hardware signer, and a coordination server — jointly control your funds through a 2-of-3 threshold scheme. Transactions require cooperation between any two parties, eliminating single points of failure while keeping the user in control.
 
@@ -18,7 +18,7 @@ Three independent identities — your phone, a hardware signer, and a coordinati
               +---------------------+---------------------+
               |                                           |
 +-------------+--------------+             +--------------+-------------+
-|   Android Phone            |   USB OTG   |   Pico 2 Hardware Signer  |
+|   Android Phone            |   USB OTG   |   HW Signer (RP2350)     |
 |   Flutter App              +-------------+   Embassy firmware         |
 |   Identity 1/3             |   HID 64B   |   Identity 2/3            |
 |   Signing + wallet logic   |   reports   |   Recovery key in flash   |
@@ -28,7 +28,7 @@ Three independent identities — your phone, a hardware signer, and a coordinati
 | Identity | Held by | Purpose |
 |----------|---------|---------|
 | **Signing** | Phone (local) | Day-to-day transaction signing |
-| **Recovery** | Pico 2 (USB HID) | Policy changes, recovery operations |
+| **Recovery** | HW Signer (USB HID) | Policy changes, recovery operations |
 | **Server** | Coordination server | Co-signs transactions, never learns the full key |
 
 Any 2-of-3 can produce a valid Taproot (BIP-340) signature. The server alone cannot move funds.
@@ -43,10 +43,10 @@ MPCWallet/
 +-- threshold-ffi/      C-ABI shared library wrapping threshold for Dart FFI
 +-- server/             Rust gRPC coordination server (Wasmtime + cosigner WASM)
 +-- cosigner/           WASM cosigner component (server-side threshold crypto)
-+-- pico-signer/        Raspberry Pi Pico 2 firmware (Embassy + USB HID)
++-- hwsigner/           Hardware signer firmware (Embassy + USB HID, RP2350)
 +-- protocol/           gRPC stubs and proto definitions
 +-- e2e/                End-to-end integration tests (includes signer-server)
-+-- scripts/            Utilities (bitcoin.sh, test_pico.py, udev rules)
++-- scripts/            Utilities (bitcoin.sh, test_hwsigner.py, udev rules)
 +-- docker-compose.yml  Bitcoin regtest environment (bitcoind + electrs)
 +-- Makefile            Build, flash, and run targets
 ```
@@ -61,7 +61,7 @@ High-level Dart API that orchestrates the full MPC protocol. Manages two local i
 
 ### Threshold Library (`threshold/`)
 
-`#![no_std]` Rust implementation of FROST (Flexible Round-Optimized Schnorr Threshold Signatures) over secp256k1 using the `k256` crate. Includes the full 3-round DKG protocol, Pedersen VSS, nonce commitment generation, signature share computation, Lagrange interpolation, Taproot key tweaking, and key refresh. Compiles for four targets: native (tests & server), `wasm32-wasip1` (cosigner), `thumbv8m.main-none-eabihf` (Pico 2), and Dart FFI (`libthreshold_ffi.so`).
+`#![no_std]` Rust implementation of FROST (Flexible Round-Optimized Schnorr Threshold Signatures) over secp256k1 using the `k256` crate. Includes the full 3-round DKG protocol, Pedersen VSS, nonce commitment generation, signature share computation, Lagrange interpolation, Taproot key tweaking, and key refresh. Compiles for four targets: native (tests & server), `wasm32-wasip1` (cosigner), `thumbv8m.main-none-eabihf` (hwsigner), and Dart FFI (`libthreshold_ffi.so`).
 
 ### Threshold FFI (`threshold-ffi/`)
 
@@ -75,13 +75,13 @@ Rust gRPC server that participates as the third identity in DKG and signing. Eac
 
 WASI P2 Component Model guest that encapsulates all threshold cryptography on the server side. Compiled to `wasm32-wasip1` and loaded by the server into per-user Wasmtime instances. Exposes DKG, nonce generation, signing, and key refresh operations through a WIT interface. Shares no memory between users.
 
-### Pico Signer Firmware (`pico-signer/`)
+### HW Signer Firmware (`hwsigner/`)
 
 Embassy-based async firmware for the RP2350 (Raspberry Pi Pico 2). Communicates over vendor-defined USB HID (64-byte reports) using a chunking protocol for JSON messages up to 8KB. Persists key material to the last 4KB flash sector after DKG. Handles all six commands: `dkg_init`, `dkg_round2`, `dkg_round3`, `generate_nonce`, `sign`, `get_info`.
 
 ### Signer Server (`e2e/signer-server/`)
 
-Standalone Rust TCP server that implements the same JSON command protocol as the Pico firmware. Used in E2E and integration tests to simulate the hardware signer without physical hardware.
+Standalone Rust TCP server that implements the same JSON command protocol as the hwsigner firmware. Used in E2E and integration tests to simulate the hardware signer without physical hardware.
 
 ## Protocol
 
@@ -95,11 +95,11 @@ Any two identities can co-sign. Each generates an ephemeral nonce pair and excha
 
 ### Spending Policies
 
-Key refresh creates additional key shares with time-windowed spending limits. Transactions below the threshold use the policy key (phone + server, no hardware signer needed). Policy updates and deletion require a recovery signature from the Pico.
+Key refresh creates additional key shares with time-windowed spending limits. Transactions below the threshold use the policy key (phone + server, no hardware signer needed). Policy updates and deletion require a recovery signature from the hardware signer.
 
 ### USB HID Chunking
 
-Messages between the phone and Pico are split into 64-byte HID reports:
+Messages between the phone and hardware signer are split into 64-byte HID reports:
 
 ```
 First report:  [channel:2][cmd:1][seq:2][total_len:2][payload:57B]
@@ -120,12 +120,12 @@ Channel `0x0101`, command `0x05` (MSG). Sequence numbers are big-endian `u16`. L
 ```bash
 # Install Rust targets
 rustup target add wasm32-wasip1                  # Cosigner WASM component
-rustup target add thumbv8m.main-none-eabihf      # Pico 2 firmware
+rustup target add thumbv8m.main-none-eabihf      # HW Signer firmware
 
 # Install cargo-component for building WASI components
 cargo install cargo-component
 
-# Install probe-rs for Pico flashing (optional, UF2 also supported)
+# Install probe-rs for HW Signer flashing (optional, UF2 also supported)
 cargo install probe-rs-tools
 ```
 
@@ -152,15 +152,15 @@ In a second terminal:
 cd ap && flutter run   # Launch on emulator
 ```
 
-### 3b. Physical device + Pico hardware signer
+### 3b. Physical device + hardware signer
 
-Flash the Pico (hold BOOTSEL, plug in USB, release):
+Flash the device (hold BOOTSEL, plug in USB, release):
 
 ```bash
-make pico-flash       # Build firmware, convert to UF2, copy to RP2350 drive
+make hw-flash         # Build firmware, convert to UF2, copy to RP2350 drive
 ```
 
-Connect your Android phone via ADB (wireless debugging recommended to free the USB port for the Pico):
+Connect your Android phone via ADB (wireless debugging recommended to free the USB port for the signer):
 
 ```bash
 adb pair <ip>:<pairing-port>     # Pair once
@@ -174,22 +174,22 @@ In a second terminal:
 cd ap && flutter run   # Select "Hardware Signer (USB)" in onboarding
 ```
 
-Connect the Pico to the phone via USB OTG adapter. The app will auto-discover it.
+Connect the signer to the phone via USB OTG adapter. The app will auto-discover it.
 
-### 4. Smoke test the Pico (no phone needed)
+### 4. Smoke test the hardware signer (no phone needed)
 
 ```bash
 # Quick: just get_info
-make pico-test
+make hw-test
 
 # Full: 2-of-2 DKG + sign with signer-server as second participant
-make pico-test ARGS="--full-dkg"
+make hw-test ARGS="--full-dkg"
 ```
 
 Requires the Python `hidapi` package (`pip install hidapi`) and the udev rule:
 
 ```bash
-sudo cp scripts/99-pico-signer.rules /etc/udev/rules.d/
+sudo cp scripts/99-hwsigner.rules /etc/udev/rules.d/
 sudo udevadm control --reload-rules && sudo udevadm trigger
 ```
 
@@ -205,8 +205,8 @@ cd threshold-ffi && cargo test
 # End-to-end (builds all deps, starts Docker automatically)
 make e2e-test
 
-# Pico firmware over USB HID
-make pico-test ARGS="--full-dkg"
+# HW Signer firmware over USB HID
+make hw-test ARGS="--full-dkg"
 
 ## Performance & Stress Testing
 
@@ -250,9 +250,9 @@ This target:
 | `threshold-ffi-build` | Build threshold FFI shared library (`libthreshold_ffi.so`) |
 | `threshold-test` | Run threshold Rust unit tests |
 | `threshold-ffi-test` | Run threshold-ffi tests |
-| `pico-build` | Build Pico 2 firmware |
-| `pico-flash` | Build, convert to UF2, and copy to RP2350 drive |
-| `pico-test` | Test Pico over USB HID (`ARGS="--full-dkg"` for full test) |
+| `hw-build` | Build HW Signer firmware |
+| `hw-flash` | Build, convert to UF2, and copy to RP2350 drive |
+| `hw-test` | Test HW Signer over USB HID (`ARGS="--full-dkg"` for full test) |
 | `adb-reverse` | Forward ports 50051 + 50001 from phone to PC |
 | `regtest` | Full dev stack: Docker + init + signer + server |
 | `regtest-hardware` | Hardware dev stack: Docker + init + ADB + server |
@@ -263,13 +263,13 @@ This target:
 ## Security Model
 
 - The **full private key never exists** on any single device.
-- The **hardware signer's secret share** never leaves the Pico's flash memory.
-- The **server cannot unilaterally sign** — it always needs cooperation from the phone or Pico.
+- The **hardware signer's secret share** never leaves the device's flash memory.
+- The **server cannot unilaterally sign** — it always needs cooperation from the phone or hardware signer.
 - The server is designed to run inside a **Trusted Execution Environment (TEE)**, ensuring the server operator cannot access key shares in memory.
 - Each user's server-side key share runs in an **isolated WASM sandbox** (Wasmtime) with no shared memory between users.
 - Signing requests are **authenticated** with Schnorr signatures over timestamped messages to prevent replay attacks.
 - Policy changes (update/delete spending limits) require a **recovery signature** from the hardware signer.
-- The Pico uses the RP2350's **hardware TRNG** for all randomness.
+- The hardware signer uses the RP2350's **hardware TRNG** for all randomness.
 
 ## References
 

diff --git a/ap/android/app/src/main/kotlin/com/example/ap/UsbHidPlugin.kt b/ap/android/app/src/main/kotlin/com/example/ap/UsbHidPlugin.kt
@@ -16,7 +16,7 @@ import io.flutter.plugin.common.MethodChannel
 import java.util.concurrent.Executors
 
 /**
- * Flutter platform channel plugin for USB HID communication with Pico Signer.
+ * Flutter platform channel plugin for USB HID communication with HW Signer.
  *
  * Exposes methods: enumerate, open, close, writeReport, readReport
  * via MethodChannel "com.mpcwallet.ap/usb_hid".
@@ -31,7 +31,7 @@ class UsbHidPlugin : FlutterPlugin, MethodChannel.MethodCallHandler {
         private const val CHANNEL = "com.mpcwallet.ap/usb_hid"
         private const val ACTION_USB_PERMISSION = "com.mpcwallet.ap.USB_PERMISSION"
 
-        // Pico Signer USB IDs (pid.codes open-source VID)
+        // HW Signer USB IDs (pid.codes open-source VID)
         private const val VENDOR_ID = 0x1209
         private const val PRODUCT_ID = 0x0001
 
@@ -77,7 +77,7 @@ class UsbHidPlugin : FlutterPlugin, MethodChannel.MethodCallHandler {
     }
 
     /**
-     * List connected USB devices matching Pico Signer VID/PID.
+     * List connected USB devices matching HW Signer VID/PID.
      */
     private fun enumerate(result: MethodChannel.Result) {
         val manager = usbManager ?: run {
@@ -104,7 +104,7 @@ class UsbHidPlugin : FlutterPlugin, MethodChannel.MethodCallHandler {
     }
 
     /**
-     * Open connection to the first matching Pico Signer device.
+     * Open connection to the first matching HW Signer device.
      */
     private fun open(result: MethodChannel.Result) {
         val manager = usbManager ?: run {
@@ -115,7 +115,7 @@ class UsbHidPlugin : FlutterPlugin, MethodChannel.MethodCallHandler {
         val device = manager.deviceList.values.firstOrNull { d ->
             d.vendorId == VENDOR_ID && d.productId == PRODUCT_ID
         } ?: run {
-            result.error("USB_NOT_FOUND", "No Pico Signer device found", null)
+            result.error("USB_NOT_FOUND", "No HW Signer device found", null)
             return
         }
 

diff --git a/ap/android/app/src/main/res/xml/device_filter.xml b/ap/android/app/src/main/res/xml/device_filter.xml
@@ -1,5 +1,5 @@
 <?xml version="1.0" encoding="utf-8"?>
 <resources>
-    <!-- Pico Signer: pid.codes open-source VID 0x1209, PID 0x0001 -->
+    <!-- HW Signer: pid.codes open-source VID 0x1209, PID 0x0001 -->
     <usb-device vendor-id="4617" product-id="1" />
 </resources>