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I'm curious what the purpose behind having a word list for BIP39 HD wallets?

Are you required to use these words to create a wallet seed?

What would happen if you chose random words not on the list, or instead a long continuous string?

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I'm curious what the purpose behind having a word list for BIP39 HD wallets?

Its a carefully chosen list so that the words are distinct and hard to confuse. For example avoiding words that sound the same but are spelled differently (e.g. MAID and MADE) but also avoiding words with similar spellings (regardless of how they sound) and avoiding long words that people often have trouble spelling.

Having a fixed list makes it easy to identify accidentally mispelled words.

Are you required to use these words to create a wallet seed?

A BIP39 compliant wallet will insist the words be in that list. There are different lists for different languages.

What would happen if you chose random words not on the list, or instead a long continuous string?

If you try to use the wallet-recovery feature and type in words not on the list, your wallet would display some sort of error message.

When creating a wallet you generally do not get to choose the words yourself. People are very poor at choosing words randomly and this results in very weak seed phrases from a security point of view.

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Technically, an HD wallet does not require a mnemonic. It simply requires entropy. The mnemonic system is designed to make human use easier, as it is far easier to write down a set of words, instead of trying to safeguard a long hex string.

The wordlists themselves are chosen to have specific properties, namely:

  1. The first four letters are unique for each word across the entire list, which makes noting it down easier, especially with compact backup devices like a cryptosteel.
  2. The list is sorted alphabetically, which makes lookup easier
  3. The list avoids words that are similar looking and sounding, which makes it easy to correct improperly noted down words.
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The bip39 algorithm is badly designed and that is why it is dependent on a specific wordlists. Each time you want to add a new language you have to update the BIP!

Electrum has it's own seed mnemonic format that does not depend on specific wordlists so it's definitely possible to create a format like that.

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"Are you required to use these words to create a wallet seed?"

BIP39 starts with a randomly generated number, usually 128-256 bits long. The mnemonic is a representation of this number, in 12-24 words.

The point in using the mnemonic is that simply using a 128-256 bit number is cumbersome and prone to transcription errors when trying to restore your seed on HD wallets. Copying 12-24 words is easier and less susceptible to human error.

You do not necessarily need to use the English wordlist, of course. Alternatives in other languages are available.

"What would happen if you chose random words not on the list, or instead a long continuous string?"

Probably nothing (or an error message), but it depends on which wallet software you are using to restore with. Electrum will use any words you give it, so that's an exception.


You can use any source you like to generate your own 128-256 bit number, and each number will be represented with a unique 12-24 word BIP39 mnemonic. You can use this mnemonic to move your HD keys from one wallet software to the next, or even a hardware wallet, if you prefer.

You could hash any combination of words you like in order to create a 128-256 bit number, but that would be venturing into brainwallet territory. Generating a number randomly is more secure, though.

Is there any reason in particular you don't like the existing wordlist options? The words themselves are really not very important, rather they just make restoring your HD seed easier. Your results won't be "more random" or "more secure" just because you are using a different wordlist. It's kind of like representing a number in Arabic rather than Roman numerals, or vice versa. They still represent the same number.

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