Both Passport Core and Passport Prime generate your seed using multiple independent hardware sources of randomness, including an open source avalanche noise source. For the vast majority of people, letting the device do this is the right choice.
Some advanced users prefer to supply their own randomness instead, either because they want to see exactly where every word of their seed came from, or because they do not want to rely solely on the device's hardware. This is known as user added entropy, and the video below walks through the process on both devices.
What is User Added Entropy?
Your seed is simply a very large random number, presented to you as 12 or 24 BIP39 words. Normally your Passport produces that number for you. With user added entropy, you produce it yourself by drawing words at random from the BIP39 word list , then entering those words onto the device.
The final word of a BIP39 seed is special. Rather than being purely random, it contains a checksum that has to match the words before it. This means you cannot simply pick every word at random and expect a valid seed, which is why your Passport can calculate that last word for you.
This is an advanced feature and the responsibility for the quality of your randomness shifts entirely to you. A seed generated from a poor or predictable source of entropy can be guessed by an attacker, resulting in the complete loss of your funds. If you are not confident in your method, allow your Passport to generate the seed for you.
How It Works
The process is the same on both Passport Core and Passport Prime:
- Print the BIP39 word list , which contains all 2048 possible words, then cut out each word individually
- Place every word into a hat, bowl, or similar container and mix them thoroughly
- Draw out one word at a time and write it down, returning each word to the container and mixing again before the next draw, so that every word remains equally likely each time
- Repeat until you have 11 words (for a 12 word seed) or 23 words (for a 24 word seed)
- Enter your words onto your Passport
- Choose Generate Final Word and your Passport calculates the valid checksum word that completes your seed
Both devices use predictive text entry to speed up word entry. To enter car, for example, you only need to type 2-2-7 and your Passport will display all of the matching words.
Where to Find It
Passport Core (firmware 2.3.0 and later) offers this when importing a seed. See the Passport Core Setup Guide for the full seed entry flow.
Passport Prime offers this when entering BIP39 seed words, either during setup by choosing Restore, or at any time from the Vault app using Import Item, then Import Seed Words. See the Passport Prime Setup Guide for the full restore flow.