Generating a Mnemonic
Krux has support for creating 12 and 24-word mnemonic seed phrases. Since true entropy is difficult to produce, especially with an embedded device, we recommend to outsource entropy generation using dice rolls, but it is also possible to use camera as a source of entropy to quickly create a mnemonic.
At the start screen, once you select New Mnemonic, you will be taken to a second menu where you can choose to create a mnemonic via camera, via rolls of a D6 (standard six-sided die) or D20 (20-sided die).
Camera¶
(Experimental!) Choose between 12 or 24 words, then take a random picture and Krux will generate a mnemonic from the hash of the image bytes.
Image Entropy Quality Estimation¶
During image capture, entropy quality estimation is displayed to assist you in obtaining a high-quality image source for your key. After a snapshot is taken, Shannon's entropy and pixel deviation indices are presented. Minimum thresholds are established to prevent the use of poor-quality images with low entropy for key generation. It's important to note that these values serve as indicators or estimations of entropy quality, but they are not absolute entropy values in a cryptographic context.
Dice Rolls¶
Via D6¶
Choose between 12 or 24 words.
The entropy in a single roll of a D6 is 2.585 bits ( log2(6) ); therefore a minimum of a 50 rolls will be required for 128 bits of entropy, enough to generate a 12-word mnemonic. For 24 words, or an entropy of 256 bits, a minimum of 99 rolls will be required.
Via D20¶
Since a D20 has more possible outcomes, the entropy is increased per roll to 4.322 bits ( log2(20) ). This means that only 30 rolls are necessary to create a 12-word mnemonic and 60 rolls for a 24-word mnemonic.
Dice Rolls Entropy Quality Estimation¶
When you input your dice rolls, you'll see two progress bars filling up. The top progress bar shows how many rolls you've entered compared to the minimum number needed. The bottom progress bar shows the real-time calculated Shannon's entropy compared to the required minimum (128 bits for 12 words and 256 bits for 24 words). When the Shannon's entropy estimation reaches the recommended level, the progress bar will be full, and its frame will change color. If you've met the minimum number of rolls but the entropy estimation is still below the recommended level, a warning will appear, suggesting you add more rolls to increase entropy. Note: Similar to image entropy quality estimation, dice rolls Shannon's entropy serves as an indicator and should not be considered an absolute measure of cryptographic entropy.
Stats for Nerds¶
A low Shannon's entropy value might suggest that your dice are biased or that there's a problem with how you're gathering entropy. To investigate further, examine the "Stats for Nerds" section to check the distribution of your rolls and look for any abnormalities.
How it works¶
For dice rolls, Krux keeps track of every roll you enter and displays the cumulative string of outcomes after each roll.
When you have entered your final roll, Krux will hash this string using SHA256 and output the resulting hash to the screen so that you can verify it for yourself.
In the case a camera snapshot is used as source, image bytes, which contain pixels data in RGB565 format, will be hashed just like it is done with the dice rolls string.
Krux then takes this hash, runs unhexlify on it to encode it as bytes, and deterministically converts it into a mnemonic according to the BIP-39 Reference Implementation.
Note: For 12-word mnemonics, only the first half of the SHA256 hash is used (128 bits), while 24-word mnemonics use the full hash (256 bits).
How to verify¶
Don't trust, verify. We encourage you not to trust any claim you cannot verify yourself. Therefore, there are wallets that use compatible algorithms to calculate the entropy derived from dice rolls. You can use the SeedSigner or Coldcard hardware wallets, or even the Bitcoiner Guide website, they share the same logic that Krux uses and will give the same mnemonic for the dice roll method.
Alternatives¶
You can use any other offline airgapped devices to generate your mnemonic. If you have an old Android smartphone that is offline (in airplane mode [no active CDMA or GSM chip], no Wifi connection, no Bluetooth and localization service turned off), you can use the Krux app for Android. If you want to use a regular PC, a common strategy is to boot the PC using Tails from a USB stick, without connecting the device to the internet, and then you can run Krux using our simulator, use a copy of the the Bitcoiner Guide website or even Ian Coleman's BIP-39 Tool. It's worth noting that both generate a QR code that Krux can read via the QR input method mentioned on the next page (Loading a Mnemonic).