entrops

Interfaces for reading entropy from a PRG320 hardware random number generator (HWRNG) by Ingenieurbüro Bergmann, connected via USB serial (FTDI FT232R).

Hardware

• Device: PRG320
• Interface: USB serial (appears as /dev/ttyUSB0, /dev/ttyUSB1, ...)
• Baud rate: 921600
• Output: raw bytes terminated by \n

Multiple devices are supported simultaneously.

Development

$ nix-shell
$ cargo build --release

Binaries

One-shot CLI

Reads a single sample from /dev/ttyUSB0 and prints JSON to stdout.

$ cargo run

{
  "hex": "a3f1...",
  "int": 174832...,
  "raw": "[163, 241, ...]"
}

serve - web server

Streams live entropy data from all connected USB serial devices.

$ cargo run --bin serve

Starts two listeners:

Port	Protocol	Description
3003	HTTP	Web UI, REST API and SSE stream
3004	TCP	Raw hex stream (newline-delimited)

Web UI

Open http://localhost:3003 in a browser. Each connected device gets a live-updating panel showing the current hex output. A Stop/Start button pauses and resumes the stream.

REST API

All endpoints return a JSON array with one entry per device. Samples are collected fresh on each request (up to 15 s timeout).

Endpoint	Response fields
GET /api	timestamp, hex, int, raw
GET /api/hex	timestamp, hex
GET /api/int	timestamp, int
GET /api/raw	timestamp, raw

• timestamp is Unix epoch milliseconds recorded immediately after the port read completes.
• raw is the debug representation of the byte slice, e.g., [163, 241, 10].

Example:

$ curl http://localhost:3003/api/hex

[{"timestamp": 1750000000123, "hex": "a3f10a..."}]

SSE stream

$ curl -N http://localhost:3003/stream

Emits one event per sample across all devices:

data: {"device":"/dev/ttyUSB0","hex":"a3f10a","int":"10743050"}

TCP stream

Connect with netcat to receive a continuous newline-delimited HEX stream:

$ nc localhost 3004

a3f10a...
c72e91...

Each line is the hex-encoded output of one sample. Multiple concurrent clients are supported. The connection closes cleanly when the client disconnects.

Feeding entropy to the kernel with rngd

rngd (from rng-tools) reads from a entropy source and writes into the kernel entropy pool (/dev/random), increasing the available entropy for cryptographic operations.

Directly from the serial port

Configure the port baud rate and hand it to rngd:

$ stty -F /dev/ttyUSB0 921600 raw -echo
$ rngd -r /dev/ttyUSB0 -o /dev/random

For multiple devices, run one rngd instance per port.

Via the TCP stream

The TCP endpoint emits hex-encoded samples. Decode on the fly and pipe into rngd using a named pipe:

$ mkfifo /tmp/entropy
$ nc localhost 3004 | xxd -r -p > /tmp/entropy &
$ rngd -r /tmp/entropy -o /dev/random -f

Testing entropy quality with rngtest

rngtest (also from rng-tools) runs FIPS 140-2 statistical tests against the byte stream:

$ nix-shell -p rng-tools tinyxxd
$ nc localhost 3004 | xxd -r -p | rngtest -c 1000
rngtest 6.17
Copyright (c) 2004 by Henrique de Moraes Holschuh
This is free software; see the source for copying conditions.  There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

rngtest: starting FIPS tests...
rngtest: bits received from input: 10000032
rngtest: FIPS 140-2 successes: 500
rngtest: FIPS 140-2 failures: 0
rngtest: FIPS 140-2(2001-10-10) Monobit: 0
rngtest: FIPS 140-2(2001-10-10) Poker: 0
rngtest: FIPS 140-2(2001-10-10) Runs: 0
rngtest: FIPS 140-2(2001-10-10) Long run: 0
rngtest: FIPS 140-2(2001-10-10) Continuous run: 0
rngtest: input channel speed: (min=1.483; avg=41.093; max=19531250.000)Kibits/s
rngtest: FIPS tests speed: (min=60.551; avg=171.389; max=323.279)Mibits/s
rngtest: Program run time: 250446315 microseconds

A healthy PRG320 output should produce zero failures across all test categories.