HSM4 FAQ & Troubleshooting

A: Check the following:

1. Check that the Raspberry Pi power is sufficient. The red LED on most Raspberry Pi models indicates if the Pi is being powered adequately. If it is not lit at all or flashes intermittently, try a different power supply or a different USB cable.

2. Make sure that you have enabled i2c support using raspi-config BEFORE your install the software. Also, when you enable i2c communications be sure to follow the enable-disable-enable sequence.

3. If i2c support has been enabled correctly and the HSM4 LED is still rapidly blinking, check proper physical installation of the HSM4 as detailed in this “Getting Started” guide.

4. HSM4 uses GPIO header pins 3 and 5 for i2c communications and pin 7 as an interrupt signal to the Pi. Pin 7 should preferably be dedicated exclusively to HSM4. Other devices may share the i2c bus with HSM4, but there may still be address conflicts. By default, HSM4 uses slave address 0x30. If the address conflict cannot be resolved on the other i2c devices, there is a way of changing the i2c address through an API call. Using this application, the HSM4 address can be changed anywhere in the ranges of 0x30-0x37 or 0x60-0x67.

5. Oftentimes the 1-Wire interface relies on pin 7 (GPIO 4) for communication. If the 1-Wire interface is enabled, try disabling through raspi-config. If that resolves the problem take steps to either move the HSM4 interrupt signal from GPIO 4 or the 1-Wire interface from GPIO 4.

6. if the directory at /var/lib/zymbit or any of the files and/or subdirectories are corrupted or deleted, the HSM4 will fail to work. IMPORTANT: if this happens when the HSM4 is locked (i.e. Production Mode), the HSM4 can never be used again.

A: This issue could be caused by the same issues described in the first question (Why does the LED continue to blink rapidly?). Additionally, this can be caused if a locked (Production Mode) HSM4 is moved to another Pi.

1. 1 second very rapid flash, 1 second off, 8 slow blinks
   • This indicates interrupted communications.

2. 1 second very rapid flash, 1 second off, 5 slow blinks
   • This indicates a failure to communicate with ATECC. The most likely cause is the HSM4 is in Production Mode, tamper detect was set to self-destruct, and a tamper detect event caused the HSM4 to self-destruct. If tamper detect is not armed, this indicates a hardware problem.

3. Constant rapid blinking (waiting for host to connect)
   • This indicates that you HSM4 is operational but has not bound to the host. If the HSM4 continues to blink this pattern, it could mean that there is a problem with the host Pi or that the i2c is not configured or that the i2c and wake pins are not making contact.

4. Once every 3 seconds
   • This indicates that your HSM4 is working and running.

5. Three rapid blinks every 3 seconds
   • This indicates the HSM4 is in Production Mode and is working and running.

6. Rapid blinking then LED off permanently
   • This indicates the HSM4 is in Production Mode but cannot bind with the RPi / SD card pair. In Production Mode the binding with a particular Pi and SD card becomes permanent. Most likely cause for this is that the HSM4, the SD card, or the PI has been swapped out.

A: You can change the I2C address through our standard APIs:

• C: int zkSetI2CAddr ( zkCTX ctx, int addr)
• Python: set_i2c_address

The I2C communication between the Zymkey and the Host is encrypted, but will not interfere with other devices on the same bus (assuming there is no address conflict).

See API Documentation

A: HSM4 monitors the quality of 5V power coming into the host computer. If the voltage drops below a specified limit, even momentarily, then HSM4 will disable all security services to the host. This is a security feature to prevent power cycle and brown-own attacks. If you are powering a display, modem, or other power-hungry device from your Pi, then check the capacity and quality of your power supply. Learn more >

A: Some people have become accustomed to using i2c-detect to do a first level check for correct installation and baseline functionality of i2c devices. However, these tools only really work if the i2c device communicates via a protocol that sits on top of i2c called SMBus or SMB (System Management Bus). Instead, HSM4 communicates to the host at a much more fundamental level, in part because the HSM4 protocol traffic is encrypted.

You can tell if you successfully installed it by observing the blue LED. If it is flashing once every 3 seconds, then binding completed. You can also use the systemctl command. It should say “active (running)”:

systemctl status zkifc

A: Yes, you should have no problem running it multiple times if it were to fail.

A: lsblk will show you the partitions. Look for the name of your / partition (default is mmcblk0p2) and the USB device (default is sda). Example output:

NAME         MAJ:MIN  RM   SIZE  RO TYPE  MOUNTPOINT
mmcblk0      179:0    0   14.9G   0  disk
|-mmcblk0p1  179:1    0    256M   0  part   /boot
`-mmcblk0p2  179:2    0   14.6G   0  part   /
sda            8:0    0   32.0G   0  disk
|_sda1         8:1    0   32.0G   0  part

A: Once you get to the second phase and login, you can monitor progress with

journalctl -fu cfg_SD_crfs

That will show you progress of the second half of the encryption process.

A: The script is designed to re-use information on the USB stick to encrypt a “golden” image in production on more than one device. If the file original_zk_root.tgz exists on the USB stick, it will use that file and skip the step of creating a whole new tarball of the rootfs. If you truly want to start over, start by reformatting/erasing your USB stick.

A: The script attempts to unmount the external device, but in some cricumstances the device may stay mounted and the process will fail. You will get a message either on your screen or in journalctl -fu cfg_SD_crfs during the second phase indicating the drive was already mounted. Unmount the drive and try again.

# Check /dev/sda* mount points for devices mounted to /media/*
lsblk

# if mounted, unmount
sudo umount /media*

# re-run service
sudo systemctl restart

# monitor progress
journalctl -fu cfg_SD_crfs

A: Since zkifc is stopped during the process, the blue LED will flash rapidly until the whole process completes. Once both of the automautic reboots are completed, the blue LED will return to flashing once every 3 seconds.

lsblk will show you that you now have a “cryptrfs” partition under your mmcblk0p2 (default)

df -h will also show “/dev/mapper/cryptrfs” for the “/” file system.

If your system reboots twice, the LED returns to flashing once every 3 seconds, and lsblk displays a “cryptrfs” partition, you can be confident your system is encrypted and protected.

Zymkey and HSM4: NIST P-256 and secp256r1

HSM6: NIST P-256, secp256r1, secp256k1, X25519, ED25519

A: The easiest way is to save the HSM4 key directly to a binary file, copy that file to the HSM6 and read in the binary file.

HSM4 side:

#!/usr/bin/python3
import zymkey

# Get the public key from slot 0 and save it in a file
pub_key_file = '/tmp/pub_key_slot0'
slot = 0
key = zymkey.client.get_public_key(slot)
with open(pub_key_file, "wb") as f:
    f.write(key)

copy /tmp/pub_key_slot0 over to the HSM6 PI

HSM6 side:

#!/usr/bin/python3
import zymkey

key_file = "/tmp/pub_key_slot0"
key = open(key_file, "rb").read()
# Store the key in the foreign key store
foreign_slot = zymkey.client.store_foreign_public_key('secp256r1', key)

A: The clock will sync to the current timestamp once the Pi has achieved NTP sync. This requires you to have access to the Internet.

A: For Zymkey and HSMs, kernel drivers and libraries for all of the devices are included in the Zymkey software package via the APIs.

A: You can update your existing key with the following command:

curl -L https://zk-sw-repo.s3.amazonaws.com/apt-zymkey-pubkey.gpg | sudo gpg --dearmor --yes -o /usr/share/keyrings/zymbit.gpg

A: No, but perimeter detect can be configured to prevent access to the SD card. When a tamper event is detected, the HSM4 will, when properly configured via the API, destroy all critical key material and the root fs will fail to be decrypted upon boot.

A: The following table compares Zymkey and HSM operational modes while connected to Main Power, Battery Power, and No Power.

The battery is required to maintain the Real Time Clock and the perimeter detect circuits when the host power is removed. Without the battery, these two functions will not be active when the host power is removed.

A: If the battery dies and the host is not connected to power, some features will go out, such as Perimeter Detect and Real Time Clock. See the table below for more information.

With Zymkey and HSM4, if tamper detect is enabled and the battery dies or is removed, the device will self-destruct. This is an intentional security feature. If tamper detect is NOT enabled, you should connect the host device to power to change the battery.

HSM6 has a battery monitoring feature to help the user prevent the battery from dying. If the battery dies, HSM6 users have the ability to choose whether the device should self-destruct or hold in reset mode until the battery is changed.

A: Someone could easily replace the kernel and, while it is possible to configure initramfs to not permit the busybox shell to, that can be sidestepped as well. Even if you hack your own changes to the kernel to ignore the init option, someone could replace your kernel. Also, kernel updates would have to be done manually and the updates from the apt repo would have to be blacklisted.

A: There are many reasons why this is infeasible, but the main one is that, since the GPU initially functions as a bootloader processor during boot and since Broadcom has not made the GPU compiler publicly available as well as the source code for the bootloader, one cannot simply compile their own code that would ignore cmdline.txt.

A: No because the GPU bootloader does not have encryption features implemented and, even in lieu of that, it does not know how to communicate with HSM4. The best solution, then, would be to implement an independent secure boot procedure. As mentioned above, we are currently working on adding this feature in a future product.

A: Self-destruct mode works only after the Lock Tab has been cut.

A: No, once turned on, “self-destruct” mode is permanent.

• The SBC and SD card hardware will be reusable.
• Because the SD card contents are encrypted and the decryption key was destroyed, the data is lost.
• The HSM4 will not be reusable because the key slots will be destroyed.

A: No. Cutting the Lock-Tab permanently binds that instance of HSM4 to the specific instances of host computer and SD card. This is a security feature to prevent credentials being moved from one host to another. DO NOT cut the Lock-Tab if you are still in development and expect to change the host or SD cards.

A: Yes, because HSM4 is battery powered. As long as the battery is sufficiently charged, it will still self-destruct.

A: Sign up for our new product email updates at the bottom of Zymbit’s homepage.

• Electrically, the Zymkey-I2C will interface to any single board computer using I2C. Check compatibility with your particular Linux distribution.
• Raspberry Pi 3, 3B+, 4, Zero
• RPi Compute Module 3, 4

A: We have no plans to release an Arduino shield version. While we love Arduinos and use them all the time, they generally don’t have enough resources to handle cryptographic operations at this level.

A: Zymbit does not officially support the BeagleBoard platform at this time.

• HSM4-RPi (3.3V): idle approx. 1mA; max active < 25mA with LED off, < 35mA with LED on.
• HSM4-USB (5V): idle approx. 1.5mA; max active < 40mA with LEDs off, < 60mA with LEDs on.

See Power Quality for more information.