Subject: Re: [bitcoindev] BIP39 Extension for Manual Seed Phrase Creation

From: pithosian <[email-masked]>
Date: Sat, 24 May 2025 20:56:08 +0000 (UTC)

BIP39 works fine with entropy generated without a computer. I
personally recommend using coinflips with Von Neumann skew correction.

Yes, you need to perform a SHA256 hash to calculate the checksum word.

You need to use SHA512 HMAC as the next step, and EC point
multiplication along with a host of other steps which are unrealistic
to expect a human to perform by hand to actually get child keys and
addresses out the other end, too.

I have a bootable UEFI application for generating a mnemonic with
skew-corrected coinflips (among other things), designed for airgapped
operation, lying around in my archive somewhere. I plan on
re-implementing it as part of a much larger, long-running project but
if there's interest I can go find it, clean it up and publish the
old version in the meantime.

The spec doesn't need to change; there's really no benefit to
generating a mnemonic without the SHA256 hash step, because again, you
can't do anything with that mnemonic without hashing.

As for encoding derivation paths in the mnemonic, Electrum's Seed
Version System achieves roughly the same thing, but descriptors are a
better solution for managing non-entropy metadata for wallets.

For those who really don't want to put in the small amount of additional
effort required to use descriptors, replying on the standard derivation
paths is sufficient, as long as they're made aware of their existence.
Educating your users is a better solution than attempting to abstract
away (aka hide) critical information from them.

On Fri, 23 May 2025 13:15:41 +0000 (UTC)
Eric Kvam <[email-masked]> wrote:

> *Motivation*
> Make it easy for users to manually create their seed phrase so that
> they don't have to trust a "black box" and allow for encoding
> derivation path in seed phrase to simplify recovery
> 
> *How*
> Use every eighth word from the wordlist to generate 16 word phrases
> with 128 bits of entropy (no checksum).  The most significant eight
> bits of each word are used as entropy.  The least significant three
> bits of each word specify the derivation path.
> 
>    - *000* Derivation Path Not Specified
>    - *001* m/44'/0'/0'
>    - *010* m/49'/0'/0'
>    - *011* m/84'/0'/0'
>    - *100* m/48'/0'/0'/2'
>    - *101* m/86'/0'/0'
> 
> Up to seven derivation paths can be specified if all words have the
> same least significant bits.  If the least significant bits of each
> word vary, there are 48 bits that can be used to encode meta-data.
> As long as meta-data is limited to certain allowable values, this
> provides a mechanism for error detection, similar to a checksum.
> 
> *Benefits of Suggested Implementation*
> 
>    - The word length determines how the seed phrase should be
> interpreted. User only needs to know how many words they have and how
> many words the wallet supports to check for compatibility with this
> extension
>    - Uses same wordlist to represent the same entropy as a 12 word
> phrase (could be a revision to BIP39 instead of a new BIP)
>    - Manual procedure is very simple, each derivation path can use a 
>    shortened 256 word list which enjoys improved alphabetical
> separation of words
>    - May prevent naive word selections which aren't limited to every
> eighth word (similar to what checksum does)
>    - Can be extended further.  For example, a 32 word phrase with the
> same entropy as a 24 word phrase could also be added.  We can keep
> adding formats with unique word length and keep adding uses for the
> meta data as needed.
> 

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