Nitrokey TRNG RS232 Firmware

Infnoise inspired serial TRNG implementation for NetHSM

Production

• Download the firmware from the release page
• Download the dfu-upload.sh script and place it in the same folder
• Connect a device that you want to flash via USB
• Run ./dfu-upload.sh firmware

Getting Started

• Install Docker

• Install DFU-Programmer:

  • Linux: $ apt-get install -y dfu-programmer
  • MacOS: $ brew install dfu-programmer

Build & Upload

Go to src directory:

$ cd src

Build:

$ make docker-build

Flash:

1. Get the Atmega16u2 into DFU-mode
2. $ make dfu

Build & Flash:

1. Get the Atmega16u2 into DFU-mode
2. $ make

On some systems the make dfu command needs sudo privilege.

DFU mode:

New (previously unflashed) Atmega16u2 always boot directly in DFU mode.

On development boards:

1. permanently close JP1
2. connect board over USB
3. shortly close JP2

Monitor random data output

Linux:

$ stty 115200 raw cs8 -cstopb -parenb -F /dev/[serial device]
$ xxd /dev/[serial device]

MacOS:

$ (stty 115200 raw cs8 -cstopb -parenb; xxd) </dev/[serial device]

Serial device would be something like ttyS0 or cu.usbserial-XXX.

Check entropy

With the ent tool the entropy can be estimated:

Linux:

$ dd if=/dev/[serial device] iflag=fullblock bs=1K count=100 | ent 

MacOS:

(stty 115200 raw cs8 -cstopb -parenb; dd iflag=fullblock bs=1K count=100) </dev/[serial device] | ent

This should result in output similar to:

100+0 records in
100+0 records out
102400 bytes transferred in 9.188599 secs (11144 bytes/sec)
Entropy = 7.998317 bits per byte.

Optimum compression would reduce the size
of this 102400 byte file by 0 percent.

Chi square distribution for 102400 samples is 238.57, and randomly
would exceed this value 76.25 percent of the times.

Arithmetic mean value of data bytes is 127.5779 (127.5 = random).
Monte Carlo value for Pi is 3.140982070 (error 0.02 percent).
Serial correlation coefficient is -0.000348 (totally uncorrelated = 0.0).

Hardware

The schematic can be found insed the hardware repository.

License