How to generate a Seed Phrase.

TL;DR (concentrated takeaways)

When you have your own crypto wallet, you have a few choices for how to generate your seed phrase:

The Vault12 Guard app can generate a secure seed phrase for you.

You could let your digital wallet generate a seed phrase for you. Or for very high security, you could "roll your own" seed phrase with dice or a calculator as offline methods.

It is extremely important that your seed phrase be randomly generated, so that it cannot be guessed or reverse-engineered.

1. How to generate a seed phrase with Vault12?

Vault12 can help you to easily create an encrypted and distributed digital vault. The Vault12 Guard app secures all sorts of digital assets including cryptocurrency seed phrases, and can also generate your seed phrase for you. You can be absolutely sure that your seed phrase is generated safely and automatically backed up in a secure manner. To learn more about it, please read our guide.

2. How to generate a seed phrase with a calculator?

Generating a seed phrase by using a calculator is done offline, which requires a bit of extra effort but eliminates the risk of some classes of potential online attacks. This introduces a small number of new risks, however: instead of using one device to generate your seed phrase, you'll need to use two devices: the calculator and an air-gapped computer. To create a seed phrase this way, you'll need a calculator that has a RANDOM function (for generating entropy). Learn more about generating a seed phrase using an offline calculator here.

3. How to generate a seed phrase with dice?

A humble pair of dice can be used for a non-digital and completely offline method of seed phrase generation. To do this, you'll need dice, a pen and paper, and the BIP39 word list. This method is not for the faint-hearted - be prepared to do some math! You can use a single die if you want, but it is recommended to use multiple dice. You'll be creating entropy by generating a large set of random numbers by using the dice. Learn how to generate a seed phrase with dice here.

4. How to generate a seed phrase with software crypto wallets?

With very few exceptions, most modern wallets will create your seed phrase for you when you create your wallet. This process is usually automatic, with limited options for setting the parameters of your seed phrase. For most users this one-time approach is sufficient, and it won't be thought of again.

Please take a look at the article, "Using crypto wallets to generate seed phrases" to get an overview of how seed generation is done inside wallets during the set up phase.

Optionally refer to our Crypto Wallet Guides for step-by-step instructions on how specific wallets accomplish this.

Please keep in mind, that in any potentially high net-worth use case, generating seed phrases manually on your own - especially offline - is an excellent choice since it offers much higher security and greater control over the process.

5. How to generate a seed phrase with hardware wallets?

Hardware wallets provide an extra level of security compared to software wallets, and provide methods to generate a seed phrase locally (within the wallet itself). Hardware wallets strike an excellent compromise between usability and high security. Feel free to check out Vault12's "How-to" wallet guides to bring you through the steps needed to securely generate and back up seed phrases using hardware wallets.

Here are some hardware wallets that we recommend:

• Ledger Nano X
• Ledger Nano S
• Trezor One
• Trezor Model T
• KeepKey
• ColdCard MK3
• BitBox 01/02

What goes on behind the scenes of generating a seed phrase?

In a nutshell, the process of generating a seed phrase starts with generating random data, called entropy. The entropy is then run through a hashing function - specifically SHA256 - to generate a checksum. Part of the checksum is then added to the random data. The resulting output is then split into chunks of 11 bits, where each 11-bit chunk maps to a single word on the BIP39 word list.

Confused about anything in the above paragraph? Don't worry, each step will be explained in an easy to understand format below. You can also get a higher-level understanding of seed phrase construction by checking out the article "What is BIP39?".

How much entropy should your seed phrase have? 

Generating a seed phrase HAS to begin with a RANDOM SOURCE OF DATA, otherwise an attacker could possibly steal funds by guessing or regenerating your seed phrase. Entropy is a measure of how random a set of data is.

Which offers more randomness: rolling 1 die, or rolling 2 dice? Since 2 dice have more possible outcomes, the randomness is higher. It is the same for your seed phrase. The more words that are in your seed phrase, the higher the entropy.

To successfully generate a seed phrase, the entropy generated has to fit certain parameters. The random data must be between 128 bits and 256 bits of entropy, and divisible by 32.

128 bits of entropy maps to a 12 word seed phrase

160 bits of entropy maps to a 15 word seed phrase

192 bits of entropy maps to an 18 word seed phrase

224 bits of entropy maps to a 21 word seed phrase

256 bits of entropy maps to a 24 word seed phrase

How are SHA256 and BIP39 word lists used to generate a seed phrase?

A hash function is a computer program that takes an input of data and returns a verifiable result, called a checksum. The input can be any source of data. Running the same hash function again on the same input data will always return the same checksum as the result.

For example, running your randomized source data of 128 bits of entropy through a hash function will always return the same result, so it can be used as a checksum. If the source data changes, you will get a different result from the hash function.

In this step, the random source data is run through the SHA256 hash function. The first X digits of the checksum are then added to the random source data/entropy, where X is equal to: (amount of bits of entropy / 32).

256 bits of entropy (256/32 = 8) - add the first 8 bits of the checksum to the random data

224 bits of entropy (224/32 = 7) - add the first 7 bits of the checksum to the random data

192 bits of entropy (192/32 = 6) - add the first 6 bits of the checksum to the random data

160 bits of entropy (160/32 = 5) - add the first 5 bits of the checksum to the random data

128 bits of entropy 128/32 = 4) - add the first 4 bits of the checksum to the random data

It's important to note that BIP39 generates the seed phrase from binary code, which is made up of 0's and 1's. However, the SHA256 hash function returns the checksum as a sequence of numbers and letters, called a hexadecimal. So in order to get the seed phrase, you have to convert the checksum from hexadecimal format to binary format.

Here's the next step: We slice the result into 11-bit chunks of data. Each 11-bit chunk of data will map to a word from the BIP39 word list

You have seen the word "bit" used a few times in this article. A bit represents 0's and 1's. It is the smallest representation of data we have, and it is expressed in a language our computers understand.

Your original source of random data (or entropy) plus the SHA256 checksum is divisible by 11. The BIP39 word list contains 2048 words, and each word on the list maps to 11 bits of data. In this next step, you break your entropy+checksum combo into sequential chunks of 11 bits.

It is important that you slice the 11-bit chunks in sequential order. This means going from left to right, every 11 bits is grouped together. Every 11 bits represents a word in your seed phrase, and the order of the words has to be correct.

The next step is to convert your 11-bit sequence into decimal format. This will give you a number that maps to the BIP39 word list. Now, in the correct order, map each 11-bit sequence to the matching word in the BIP39 word list. Finally, this is your seed phrase!

It's important to highlight that some word lists for BIP39 might start with 1. In code, the first number is always 0. This means that 2048 words are listed as 0-2047, not 1-2048. If your BIP39 word list starts with 1 instead of 0, you will need to subtract 1 from the word list numbers to get the correct word.

What are some different ways to perform Random Number Generation (RNG)?

Going back to generating your initial source of randomness: Once you generate the needed entropy, the remaining process of getting the seed phrase is simply math and cryptography. In practice, this means that when generating a seed phrase, the initial source of entropy is both the most important step, and also the step in which you have the most control over the result.

There are many ways to generate entropy: flipping a coin, rolling dice, dealing a deck of cards, recording ambient sound, and many more. The goal here is to get as close to true randomness as possible. If you are using a process that is not sufficiently random, an attacker could possibly recreate your seed phrase.

In the following sections of this article, we will cover different approaches for how to generate entropy, and thus generate your seed phrase.