An open-source device named Entropy32 Plus is attempting to convert radioactive decay events into Bitcoin wallet seed phrases. This device operates offline and does not rely on Wi – Fi, Bluetooth, or persistent storage; its goal is to provide a physical random source for 12-word or 24-word BIP39 seed phrases. However, the developers also indicate that this entropy source has not yet undergone independent verification and it is not recommended for handling large amounts of funds.

Collecting random events using a Geiger counter

The project repository shows that this device connects to the GMC-320S Geiger counter of GQ Electronics via a 3.5-millimeter interface, receiving pulse signals generated by radioactive sources or environmental background radiation. The circuit measures the time interval between two consecutive events and then converts these comparison results into a bitstream.

The firmware will discard measurements with equal time intervals and filter out those below 200 microseconds to reduce the impact of abnormal pulses. After the system has accumulated 512 comparison bits, it will proceed to the subsequent processing steps.

First do SHA-256, then map it to BIP39.

After the collection of raw data is completed, the device will perform processing at SHA-256. When generating a 12-word mnemonic, the first 16 bytes of the hash result are used; when generating a 24-word mnemonic, the full 32 bytes are utilized. Subsequently, the program adds a check bit according to the BIP39 specification and maps it to a standard English word list.

According to the project description, the purpose of hash processing is to reduce visible patterns caused by detector dead zones, changes in counting rates, or measurement correlations. However, this does not directly prove how much effective entropy the original physical data itself possesses.

• 12-word mode uses 128-bit data and 4-bit verification
• The 24-word mode uses 256-bit data and 8-bit verification.
• The firmware comes with a complete list of 2048 English words from BIP39.

Do not connect to the internet, and do not save mnemonics for a long period of time.

Public design documents reveal that this device does not have a wireless communication module. Users operate it through two buttons and read the mnemonic phrases on a 0.91-inch OLED screen. The generated word index is only temporarily stored in the microcontroller RAM.

After the user completes copying, they can trigger the clearance process by double-clicking to overwrite the mnemonic phrase array and restart the entropy collection process. The project also states that the original entropy pool, temporary hash values, and verification buffers will all be overwritten after processing, and the device will not write the mnemonics to persistent storage.

However, the project also acknowledges that there are no security elements in the public design, nor is there a mechanism to prove that the firmware actually installed in the device is completely consistent with the public code. This means that even if the device remains offline, assembly errors or firmware modifications can still pose risks.

Independent testing has not yet been completed.

Developer Alexander Higgins describes this project as an experimental and educational tool. The repository notes explicitly that the entropy source based on the Geiger counter has not yet been tested according to the NIST SP 800-90B standards, nor are there any independent security review results available.

He suggested first recording the original arrival time data over a long period, and then using the non-independent data minimum entropy estimation method with NIST for analysis. The project also reminded that mere statistical testing cannot prove that the entropy source is sufficiently secure.

As of September 13th, Entropy32 Plus is still in ongoing development. Code submission records show that since the project went live at the beginning of September, the firmware, circuit board, and casing designs are still being adjusted, and the repository has not yet provided a formal production version or an independent evaluation timeline.