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MultiZone® Security TEE for RISC-V processors

MultiZone® Security is the quick and safe way to add security and separation to RISC-V processors. MultiZone software can retrofit existing designs. If you don’t have TrustZone-like hardware, or if you require finer granularity than one secure world, you can take advantage of high security separation without the need for hardware and software redesign, eliminating the complexity associated with managing a hybrid hardware/software security scheme. RISC-V standard ISA doesn't define TrustZone-like primitives to provide hardware separation. To shield critical functionality from untrusted third-party components, MultiZone provides hardware-enforced, software-defined separation of multiple equally secure worlds. Unlike antiquated hypervisor-like solutions, MultiZone is self-contained, presents an extremely small attack surface, and it is policy driven, meaning that no coding is required – and in fact even allowed.

MultiZone works with any 32-bit or 64-bit RISC-V processors with standard Physical Memory Protection unit (PMP) and “U” mode.

This release of the MultiZone SDK supports the following development boards:

This repository is for the Digilent Arty A7 and the SiFive HiFive1 Rev B boards.

The Digilent Arty A7 FPGA is certified for the following bitstreams:

  • ARTY 35T: Hex Five X300 v1.0.1 RV32ACIMU – Open source. No license required.
  • ARTY 100T: SiFive E21 20G1.05.00 RV32ACIMU – SiFive evaluation license required.
  • ARTY 100T: SiFive E31 20G1.05.00 RV32ACIMU – SiFive evaluation license required.
  • ARTY 100T: SiFive S51 20G1.05.00 RV64ACIMU – SiFive evaluation license required.

Note: The Digilent Arty A7 FPGA is available in two versions: 35T and 100T. The Hex Five X300 bitstream works with the smaller 35T. The SiFive bitstreams require the larger 100T.

For instructions on how to upload the bitstream to the ARTY board and how to connect the Olimex debug head ARM-USB-TINY-H see Arty FPGA Dev Kit Getting Started Guide

MultiZone SDK Installation

The MultiZone SDK works with any versions of Linux, Windows, and Mac capable of running Java 1.8 or greater. The directions in this readme have been verified with fresh installations of Ubuntu 20.04, Ubuntu 19.10, Ubuntu 18.04.5, and Debian 10.5. Other Linux distros are similar. Windows developers may want to install a Linux emulation environment like Cygwin or run the SDK in a Linux VM guest (2GB Disk, 2GB Ram)

Linux prerequisites

sudo apt update
sudo apt install make default-jre gtkterm libhidapi-dev libftdi1-2

Ubuntu 18.04 LTS additional dependency

sudo add-apt-repository "deb focal main universe"
sudo apt update
sudo apt install libncurses-dev

Note: GtkTerm is optional and required only to connect to the reference application via UART. It is not required to build, debug, and load the MultiZone software. Any other serial terminal application of choice would do.

GNU RISC-V Toolchain

Hex Five reference build: RISC-V GNU Toolchain Linux 64-bit June 18, 2021

cd ~
tar -xvf riscv-gnu-toolchain-20210618.tar.xz

OpenOCD on-chip debugger

Hex Five reference build: RISC-V OpenOCD Linux 64-bit August 07, 2021

cd ~
tar -xvf riscv-openocd-20210807.tar.gz

Note: the SiFive HiFive1 board doesn't support OpenOCD and requires the Segger propietary package JLink_Linux_V694_x86_64.deb downloadable at

Linux USB udev rules

sudo vi /etc/udev/rules.d/99-openocd.rules

# Future Technology Devices International, Ltd FT2232C Dual USB-UART/FIFO IC
SUBSYSTEM=="tty", ATTRS{idVendor}=="0403",ATTRS{idProduct}=="6010", MODE="664", GROUP="plugdev"
SUBSYSTEM=="usb", ATTR{idVendor} =="0403",ATTR{idProduct} =="6010", MODE="664", GROUP="plugdev"

# Future Technology Devices International, Ltd FT232 USB-Serial (UART) IC
SUBSYSTEM=="tty", ATTRS{idVendor}=="0403",ATTRS{idProduct}=="6001", MODE="664", GROUP="plugdev"
SUBSYSTEM=="usb", ATTR{idVendor} =="0403",ATTR{idProduct} =="6001", MODE="664", GROUP="plugdev"

# Olimex Ltd. ARM-USB-TINY-H JTAG interface
SUBSYSTEM=="tty", ATTRS{idVendor}=="15ba",ATTRS{idProduct}=="002a", MODE="664", GROUP="plugdev"
SUBSYSTEM=="usb", ATTR{idVendor} =="15ba",ATTR{idProduct} =="002a", MODE="664", GROUP="plugdev"

# SiFive HiFive1 Rev B00 - SEGGER
SUBSYSTEM=="tty", ATTRS{idVendor}=="1366",ATTRS{idProduct}=="1051", MODE="664", GROUP="plugdev

A reboot may be necessary for these changes to take effect.

MultiZone Security SDK

cd ~
git clone

Build & load the MultiZone reference application

Connect the target board to the development workstation as indicated in the user manual.

'ls multizone-sdk/bsp' shows the list of supported targets: X300, FE310, E31, S51, PFSOC.

Assign one of these values to the BOARD variable - default target is X300.

cd ~/multizone-sdk
export RISCV=~/riscv-gnu-toolchain-20210807
export OPENOCD=~/riscv-openocd-20210807
export BOARD=X300
make load

Note: With some older versions of the ftdi libraries, the first "make load" after powering the board may take a bit longer than it should. If you don't want to wait, the simple workaround is to reset the FPGA board to abort the openOCD session. If you do this, make sure to kill the openocd process on your computer. Subsequent loads will work as expected and take approximately 10 seconds.

Important: make sure that switch SW3 is positioned close to the edge of the board.

Important: open jumper JP2 (CK RST) to prevent a system reset upon UART connection.

Run the MultiZone reference application

Connect the UART port (ARTY micro USB J10) as indicated in the user manual.

On your computer, start a serial terminal console (GtkTerm) and connect to /dev/ttyUSB1 at 115200-8-N-1

Hit the enter key a few times until the cursor 'Z1 >' appears on the screen

Enter 'restart' to display the splash screen

Hit enter again to show the list of available commands

                       Hex Five MultiZone® Security                    
    Copyright© 2020 Hex Five Security, Inc. - All Rights Reserved    
This version of MultiZone® Security is meant for evaluation purposes 
only. As such, use of this software is governed by the Evaluation    
License. There may be other functional limitations as described in   
the evaluation SDK documentation. The commercial version of the      
software does not have these restrictions.                           
Machine ISA   : 0x40101105 RV32 ACIMU 
Vendor        : 0x0000057c Hex Five, Inc. 
Architecture  : 0x00000001 X300 
Implementation: 0x20181004 
Hart id       : 0x0 
CPU clock     : 64 MHz 
RTC clock     : 16 KHz 
PLIC @0x0c000000 
DMAC @0x10040000 
UART @0x10013000 
GPIO @0x10012000 

Z1 > Commands: yield send recv pmp load store exec stats timer restart dma

Optional: Eclipse CDT Project

This repository includes an optional Eclipse CDT project for developers familiar with this IDE. No additional plugins are required to build and upload MultiZone to the target. The OpenOCD debugging plug-in is optional and recommended.

Eclipse project Setup

File > Open Projects from File System > Import source: ~/multizone-sdk

Project > Properties > C/C++ Build > Environment: set RISCV and OPENOCD variables according to your installation

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Optional: FreeRTOS Example

No additional software dependencies are required to run MultiZone-based applications. To ease the integration of the MultiZone TEE with legacy applications based on the popular FreeRTOS operating system, the MultiZone SDK includes an optional zone3.1 running FreeRTOS 10.4.0. Its functionality is identical to the one of the original zone3 that controls the robot, but it is implemented as a typical FreeRTOS applications with four tasks and one interrupt handler.


cd ~/multizone-sdk
git submodule update --init --recursive
git apply -p1 ext/freertos.patch --directory=ext/freertos


Edit multizone-sdk/Makefile and change the two references to "zone3" into "zone3.1" :


.PHONY: all 
all: clean
    $(MAKE) -C zone1
    $(MAKE) -C zone2
    $(MAKE) -C zone3
    $(MAKE) -C zone3.1
    $(MAKE) -C zone4
    $(MAKE) -C bsp/$(BOARD)/boot

    java -jar multizone.jar \
        --arch $(BOARD) \
        --config bsp/$(BOARD)/multizone.cfg \
        --boot bsp/$(BOARD)/boot/boot.hex \
        zone1/zone1.hex \
        zone2/zone2.hex \
        zone3.1/zone3.hex \


Build and load to flash with the commands “make” and “make load”.

Note: to activate MultiZone deep-sleep suspend, set configUSE_TICKLESS_IDLE 1 and configUSE_IDLE_HOOK 0 in ext/FreeRTOSConfig.h. This enables Hex Five’s optimized implementation of the FreeRTOS vPortSuppressTicksAndSleep() that takes full advantage of the RISC-V instruction wfi.

MultiZone TEE Technical Specs

Up to 4 hardware threads (zones) hardware-enforced, software-defined
Up to 8 memory mapped resources per zone – i.e. flash, ram, rom, i/o, etc.
Scheduler: preemptive, cooperative, round robin, configurable tick or tickless
Secure interzone communications based on messages – no shared memory
Built-in support for secure shared Timer interrupt
Built-in support for secure shared PLIC interrupt
Built-in support for secure DMA transfers
Built-in support for CLIC, CLINT, and PLIC interrupt controllers
Built-in trap & emulation for all privileged instructions – csrr, csrw, ecall, etc.
Support for secure user-mode interrupt handlers mapped to zones – up to 32/64 sources
Support for CPU deep-sleep suspend mode for low power applications - wfi
Formally verifiable runtime ~4KB, 100% written in assembly, no 3rd-party dependencies
C macro wrappers for protected mode execution – optional for high speed low-latency
Hardware requirements: RV32, RV32e, RV64 cpu with Memory Protection Unit and 'U' mode
System requirements: 8KB FLASH, 4KB ITIM, 2KB DTIM - CPU overhead < 0.01%
Development environment: any versions of Linux, Windows, Mac running Java 1.8 or newer

Additional Resources


Please remember that export/import and/or use of strong cryptography software, providing cryptography hooks, or even just communicating technical details about cryptography software is illegal in some parts of the world. So when you import this software to your country, re-distribute it from there or even just email technical suggestions or even source patches to the authors or other people you are strongly advised to pay close attention to any laws or regulations which apply to you. Hex Five Security, Inc. and the authors of the software included in this repository are not liable for any violations you make here. So be careful, it is your responsibility.

MultiZone and HEX-Five are registered trademarks of Hex Five Security, Inc.

MultiZone technology is patent pending US 16450826, PCT US1938774.