ArmoredWitness Applet

This repo contains code for a GoTEE Trusted Applet which implements a witness. It's intended to be used with the Trusted OS found at https://github.com/transparency-dev/armored-witness-os.

Introduction

TODO

Supported hardware

The following table summarizes currently supported SoCs and boards.

SoC	Board	SoC package	Board package
NXP i.MX6UL	USB armory Mk II LAN	imx6ul	usbarmory/mk2

The GoTEE syscall interface is implemented for communication between the Trusted OS and Trusted Applet.

When launched, the witness applet is reachable via SSH through the first Ethernet port.

$ ssh ta@10.0.0.1

date            (time in RFC339 format)?                 # show/change runtime date and time
dns             <fqdn>                                   # resolve domain (requires routing)
exit, quit                                               # close session
hab             <hex SRK hash>                           # secure boot activation (*irreversible*)
help                                                     # this help
led             (white|blue|yellow|green) (on|off)       # LED control
mmc             <hex offset> <size>                      # MMC card read
reboot                                                   # reset device
stack                                                    # stack trace of current goroutine
stackall                                                 # stack trace of all goroutines
status                                                   # status information

>

The witness can be also executed under QEMU emulation, including networking support (requires a tap0 device routing the Trusted Applet IP address).

⚠️ emulated runs perform partial tests due to lack of full hardware support by QEMU.

make trusted_applet && make DEBUG=1 trusted_os && make qemu
...
00:00:00 tamago/arm • TEE security monitor (Secure World system/monitor)
00:00:00 SM applet verification
00:00:01 SM applet verified
00:00:01 SM loaded applet addr:0x90000000 entry:0x9007751c size:14228514
00:00:01 SM starting mode:USR sp:0xa0000000 pc:0x9007751c ns:false
00:00:02 tamago/arm • TEE user applet
00:00:02 TA MAC:1a:55:89:a2:69:41 IP:10.0.0.1 GW:10.0.0.2 DNS:8.8.8.8:53
00:00:02 TA requesting SM status
00:00:02 ----------------------------------------------------------- Trusted OS ----
00:00:02 Secure Boot ............: false
00:00:02 Runtime ................: tamago/arm
00:00:02 Link ...................: false
00:00:02 TA starting ssh server (SHA256:eeMIwwN/zw1ov1BvO6sW3wtYi463sq+oLgKhmAew1WE) at 10.0.0.1:22

Trusted Applet authentication

To maintain the chain of trust the OS performes trusted applet authentication before loading it, to this end the APPLET_PUBLIC_KEY and APPLET_PRIVATE_KEY environment variables must be set to the path of either signify or minisign keys, while compiling.

Example key generation (signify):

signify -G -n -p armored-witness-applet.pub -s armored-witness-applet.sec

Example key generation (minisign):

minisign -G -p armored-witness-applet.pub -s armored-witness-applet.sec

Building the compiler

Build the TamaGo compiler (or use the latest binary release):

wget https://github.com/usbarmory/tamago-go/archive/refs/tags/latest.zip
unzip latest.zip
cd tamago-go-latest/src && ./all.bash
cd ../bin && export TAMAGO=`pwd`/go

Building and executing on ARM targets

Build the example trusted applet and kernel executables as follows:

TODO: fix this

make trusted_applet && make trusted_os

Final executables are created in the bin subdirectory, trusted_os.elf should be used for loading through armored-witness-boot.

The following targets are available:

`TARGET`	Board	Executing and debugging
`usbarmory`	UA-MKII-LAN	usbarmory/mk2

The targets support native (see relevant documentation links in the table above) as well as emulated execution (e.g. make qemu).

Debugging

An optional Serial over USB console can be used to access Trusted OS and Trusted Applet logs, it can be enabled when compiling with the DEBUG environment variable set:

make trusted_applet && make DEBUG=1 trusted_os

The Serial over USB console can be accessed from a Linux host as follows:

picocom -b 115200 -eb /dev/ttyACM0 --imap lfcrlf

Trusted Applet installation