Generate a Seed Phrase using Dice.

TL;DR (concentrated takeaways)

Using dice to choose random numbers can be an effective way to guarantee randomness.

Numbers are picked by rolling balanced dice.

Determining the correct last word takes a few extra steps.

Setting up and cleaning up the environment(s) to remove any traces of the numbers generated can take some extra steps.

1. Gather your pencil and paper, your dice, a BIP39 word list, and let's get ready to roll.

Since you are rolling multiple dice, it is important to read the results of your dice roll in the same manner for each roll - left to right, top to bottom, bottom to top, or right to left. By doing this you are removing human influence over the reading of your results. (For example, you could roll 2 and 8. This can be 28, or 82.)

In this method you will need the following denominations of dice at a minimum:

• 2xD20 dice, a 20-sided dice representing results of 1-20. It is very helpful if these dice are visually distinct from one another, as they each serve different purposes.

• 1xD100 dice, usually made up of 2x10-sided dice representing results of 0-99.

The above set of dice is what is needed to generate a single word from the BIP39 word list on each roll. It is possible to generate multiple words at the same time, speeding up the process even more. To do this, you will need the entire set of the above dice for each additional word per roll. For example, if you want to generate 3 words on each roll, you will need 3 sets of the above dice.

3. Now that you know the rules, let's start rolling.

• Shake up the dice in your hands and roll them onto a dice tray or a flat surface

• First check the indicator dice, if the result is 1, disregard the result of the D20 dice roll and move to the D100 roll result, and write down 00 as your first two digits.

• If the result of the indicator dice is not 1, check the result of the D20 dice roll and write it down on your paper using a pencil. The result is the first 2 digits of your BIP39 wordlist number.

• Check the result of your D100 dice roll. The result of the D100 roll is the last 2 digits of your BIP39 wordlist number. Using a pencil finish writing the number down on your paper.

• Repeat the above process until you have 12 numbers written down. The numbers must be written down in order, from 1-12. Changing the order of the words introduces human bias, and reduces entropy.

Let's test your knowledge. The chart below will show two examples of dice roll results and their corresponding number on the BIP39 wordlist.

How to guess the last word.

Yes, you read correctly - that last word can be guessed, however only if you have the first 11 words. This is because you already have the first 7 bits of the word already fixed as a source of entropy. And the "last" 4 bits are subject to select non-randomly, to match the checksum of the previous 128 bits.

To start, take your BIP39 word list and section it off into 16-word chunks. Next, take your 12th-word number and find which 16-word chunk it appears in. These are the 16 words that you will be trying to find which one completes your seed phrase. Only 1 of the 16 words will be accurate and complete your seed phrase.

The ideal way to do this is by using a hardware wallet. By using a hardware wallet, your seed phrase will never touch an internet-connected device. Simply start up your hardware wallet, and during setup select 'restore wallet' to enter a seed phrase. Enter the first 11 words in the wallet and then cycle through each of the 16 words as your last seed phrase word until you successfully generate your wallet.

Another method for guessing the last word is using a mnemonic code generator. Using this tool you can do the same process of trying each word of the 16-word chunk. When using a mnemonic code generator, the most important step is doing the process offline. It is best to do the process in a live operating system, like Tails OS, and never connect to the internet. If you can't use Tails, restart your computer and disable wifi and Bluetooth before proceeding.

A good mnemonic code generator is Ian Coleman's BIP39 Mnemonic Code Converter, it's open-source and trusted by the community. Simply enter your 11 words into the BIP39 mnemonic converter textbox, that you compiled from the source and is running on an offline computer, and cycle through each of the 16 words until the converter accepts your seed phrase as successful.

Using a script to find the last word.

When using a script to generate the last word, the most important step is to use a live OS like Tails, or take the necessary steps to create as sterile an environment as possible on your device. A good idea is to create a new user account on the device, and operate from that new account.

The following script is designed to be run in a web browser, with networking disabled, and in incognito mode. Once you are in a secure environment, open your web browser and open the console in developer tools. This script works by passing a variable containing your 12 words to a function, which calculates the checksum and generates the correct last word.

Checksum script code

To begin, paste the following script:
function checksum12words(data) {
if (data.length != 12) return console.log("ERROR: Need 12 words numbers as input")
let binstr = (s,l =8) => s.toString(2).padStart(l,'0')
let tohex = (bytes) => bytes.map( x => x.toString(16).padStart(2,0) ).join('')
let bytes = data.map( x => binstr(x - 1, 11)) // convert 0-index to binary
 .join('').match(/.{1,8}/g) // split 8 bits 
 .map( x => parseInt(x, 2)) // convert to UInt8
if (bytes.length != 17) return console.log("ERROR: Something is wrong, check your input")
bytes.pop() // remove wrong 17th byte of checksum
console.log("Entropy is :",tohex(bytes))
window.crypto.subtle.digest("SHA-256", new Uint8Array(bytes).buffer).then( x => {
if (x.byteLength != 32) return console.log("ERROR: Wrong SHA256")
let hash = new Uint8Array(x)
let cs = binstr(hash[0]).match(/.{1,4}/g)[0] // Thats our checksum
// Take byte 15 for full 11 bits of our final word
let bits = [binstr(bytes[15]),cs].join('')
if (bits.length != 12) return console.log("ERROR: Wrong final word bits")
//console.log(bits)
console.log("Your 12th word index is: " + (1+parseInt(bits.substr(1),2)))
 })
return "OK"

The next step is for you to add your BIP39 wordlist numbers, including the 12th word that is incorrect. This function uses the human-index numbers you generated, ie. numbers from 1 to 2048.

data = [101, 502, 962, 1400, 1607, 1817, 1090, 1827, 820, 1334, 156, 1073]

The final step is passing the data variable to the checksum12words function and calling it.

checksum12words(data)

The results of running the function will return "OK" if successful, will show you the entropy in hex, and will show you the correct final word. In our example below, the correct final word is 1078.

Entropy is : 0c87d5e0d77c8dc6220f226674d44dc3

"OK"

Your 12th word index is: 1078

Now you have your correct 12-word seed phrase! Write down the correct number for the 12th word on your paper, and clear your console history by right-clicking → clear console history. Next, restart your machine to wipe any leftover memory.

Now that you have generated your seed phrase, learn how to safely and securely back up your seed phrase, and how to import it into your favorite wallet.

After you have securely backed up your seed phrase take the following steps to ensure you leave no traces of your work. Carefully look at your BIP39 wordlist and all papers used in writing down your dice rolls, seed phrase words, and numbers. If anything is written down on paper - destroy it by burning or shredding. The purpose of destroying any paper used is to prevent someone from accessing your seed phrase by using information gathered from the papers.