DECAYKEY:
key born from decay
The security of a crypto wallet starts with how unpredictable the key is generated. DECAYKEY gets its private key not from a software algorithm, but from physics: no one in the universe knows when the K-40 atoms in natural potassium will decay. This quantum randomness becomes a key inside a cold wallet that never connects to the internet.
Why physical entropy?
Weak randomness,
empty wallet means
A significant portion of wallet thefts arose not from password cracking but from predictable key generation: in 2013, Android's SecureRandom bug affected Bitcoin wallets, and in 2023, the "Milk Sad" vulnerability (CVE-2023-39910) caused a wallet tool's weak pseudo-random number generator to cause losses of at least US$900,000. No matter how good a deterministic algorithm is, if its seed is predicted, its key is also predicted.
cannot be predicted
Radioactive decay is one of the fundamental probabilistic processes of quantum mechanics: when a single atom will decay cannot be calculated with any hidden variables. The times between events are truly random.
Radioactive as a banana
The source is natural K-40 in food grade potassium chloride; The same isotope is found in bananas, potatoes and our bodies. A sealed, few gram tablet will not deliver a significant dose outside the device; A resource that requires special permission is not used.
Don't trust a single source
The decay entropy is combined in SHA-256 with the secure chip's own hardware random number generator and optional user dice. Even if one of the sources is corrupted, the outcome remains unpredictable.
How does it work?
without degradation
to 24 words
A PIN photodiode captures K-40's beta particles; Each capture is time stamped with microsecond precision. Comparing durations between consecutive events produces unbiased bits; Bits that pass health tests are condensed with SHA-256 and converted into BIP-39 recovery words.
- Neutralization: two consecutive wait times are compared (short-long → 0, long-short → 1); Equal times are taken. The bits remain balanced even if the detector's counting rate changes.
- Health tests: The repeat count and adaptive rate tests in NIST SP 800-90B run continuously; If the source stops or light leaks, key generation will not start.
- Condensation: For a 256-bit seed, at least 1 024 raw bits are collected and compressed with SHA-256: four times the raw entropy for each output bit.
- Duration: With a few gram tablets and a close detector, a few to ten events per second are expected; The 24-word seed is ready in approximately 5–10 minutes (to be measured in the prototype). Once the key is produced, quality is important, not speed.
| source of entropy | Natural K-40 (food grade KCl, sealed tablet) + PIN photodiode |
|---|---|
| key storage | Secure chip (EAL6+ class), PIN and wipe counter |
| Link | None: No Wi-Fi, Bluetooth, NFC; USB-C charging only |
| signature | Through the air gap with QR: Bitcoin PSBT (BIP-174), Ethereum transactions |
| recovery | BIP-39 24 words, optional password; metal replacement plate |
| screen | E-ink, QR reader with camera |
| Corporate | Multiple DECAYKEY for multi-signature (e.g. 2/3) |
Working with blockchain
from the key device
never comes out
The job of a cold wallet is one thing: to keep the private key separate from the online world. The transaction is prepared in the tracking wallet on the phone or computer, scanned as a QR to DECAYKEY; The device displays the recipient address and amount on its screen, and after approval, returns the signed transaction as a QR.
tracking wallet
Knowing only the public keys, the application creates the transaction and converts it to QR. There is no private key that can be stolen on this side.
DECAYKEY
The address, amount and fee are shown on the e-ink screen; the user confirms with a physical key. The signature is made inside the secure chip.
Send to network
The signed transaction returns to the tracking wallet via QR and is published to the blockchain. The private key did not touch any wires or radios.