How to Generate Your Seed Phrase Offline with a Coin Flip

Why Use a Coin Flip?

Since the recent Coldcard exploit, the importance of verifiable, offline entropy generation has become a massive talking point. While some methods require specialized dice (like 16-sided or 20-sided dice), almost everyone has a coin lying around. By assigning binary values to heads and tails, you can easily generate truly random seed words.

What You Will Need

• Any standard coin (e.g., an American $1 coin, a quarter, etc.).
• A pen and paper.
• A device to calculate the final checksum word, such as a Blockstream Jade.
• The Blockstream offline recovery phrase guide.

Pro Tip: Always print off the binary word table rather than viewing it on an internet-connected device. This prevents any potential malware from tracking your screen time and reducing your randomness!

The Coin Flip Method

Generating a word using a coin is essentially translating your flips into binary code. We assign Heads as 0 and Tails as 1.

1. Flip your coin 11 times. Allow it to spin and land naturally on the table without interrupting it.
2. Record the result of each flip as a 0 or 1. (e.g., Tails, Tails, Heads, Tails... becomes 1, 1, 0, 1...).
3. Once you have 11 flips, use the printed binary lookup table to find the corresponding BIP39 word.
4. Write down the word and repeat this process until you have 11 words (for a 12-word seed) or 23 words (for a 24-word seed).

You might roll Tails five times in a row and think it isn't random. Remember, humans are terrible at judging randomness! As long as the coin is flipped fairly, a streak of tails is perfectly natural and mathematically sound.

Calculating the Final Checksum Word

You cannot just flip a coin for the final 12th or 24th word because that word acts as a mathematical checksum for the rest of the seed phrase. Here is how you calculate it securely offline using a Blockstream Jade:

1. Turn on an uninitialized, fully offline Blockstream Jade. (Do not connect it to Bluetooth or your computer).
2. Go to Options > Temporary Signer and select 12 words (or 24 words).
3. Use the Jade's interface to input the 11 words you generated manually.
4. When prompted for the final word, select Calculate.
5. The device will provide you with a list of mathematically valid options for your final word. Choose one, write it down, and securely store your complete seed phrase.

After calculating the word, the Jade will show you your master fingerprint. This is a crucial identifier that confirms you are in the correct wallet. Write this down alongside your seed phrase!

Final Thoughts

Once your complete valid seed phrase is generated, you can use it on any BIP39-compatible hardware wallet you prefer. You don't have to use the Jade as your daily driver if you don't want to; it's simply a fantastic offline tool for safely calculating that checksum.