cloudflare / Receipt Printer

Cloudflare Randomness Printer

The Cloudflare Randomness Printer prints on demand a 'receipt' containing the following:

1. A random number less than 1,000,000

2. A six word diceware password

3. Three passwords that have 128-bits of entropy. One has just hexadecimal digits, one has alphanumerics and another printable ASCII.

4. A random response from the Magic 8 Ball.

5. A QR code containing the information from 1 to 4.

6. A maze generated using Prim's Algorithm using a modified version of this code to make it more legible on the printer.

7. A random Sudoku generated using a modified version of this code.

8. The current UTC date and time in ISO8601 format.

The Printer

The specific printer used is a GSAN 5870W Thermal Receipt Printer but the code will work with other printers that handle the ESC/POS format (which is very common). This specific printer was only used because we had one lying around.

Random Source

The program uses /dev/urandom which is fed with entropy from Cloudflare's internal randomness source (such as lava lamps)

Button

The code above runs on a Raspberry Pi Model B with an LED and a button connected to two GPIO ports. Pressing the button simply executes ep.py. It uses code similar to this:

import RPi.GPIO as GPIO
import time, os

GPIO.setmode(GPIO.BCM)
GPIO.setwarnings(False)
GPIO.setup(18, GPIO.IN, pull_up_down=GPIO.PUD_UP)
GPIO.setup(25, GPIO.OUT)

while True:
    input_state = GPIO.input(18)
    if input_state == False:
        GPIO.output(25, GPIO.HIGH)
        os.system("python ep.py")
        GPIO.output(25, GPIO.HIGH)
    time.sleep(0.01)

The button is connected between GND and GPIO18. The LED is connected between GND and GPIO25 with a 330 Ohm resistor to GND.