seed-split

A tool to split seed phrases into shares.

For example, you can generate a seed phrase:

$ seed-split random
genre cradle verb jazz super pizza silver limit hungry grace choose sing

Then, you can split that seed phrase into 3 shares:

$ seed-split split -t 2 -n 3
Seed Phrase:
genre cradle verb jazz super pizza silver limit hungry grace choose sing
1 father day shaft path tilt festival loud crystal fence fan immune section
2 liquid captain owner such put during festival silly bracket acquire oppose target
3 rail cloth portion avocado nice regret border lab calm culture second stock

Since we've used a threshold of 2, any 2 of these shares are enough to reconstruct the seed phrase:

$ seed-split combine 2
1 father day shaft path tilt festival loud crystal fence fan immune section
3 rail cloth portion avocado nice regret border lab calm culture second stock
Reconstructed:
genre cradle verb jazz super pizza silver limit hungry grace choose sing

The advantage of this approach is that you can store the seed phrase over different media, or even with different people. For example, continuing with threshold of 2, you could give one share to a friend, which isn't enough to reconstruct the seed phrase by itself, but would serve as a backup if you were to lose one of the other two shares.

Security

This is experimental software, use at your own risk.

Usage

seed-split 0.1.0
Split a seed phrase into multiple shares.

USAGE:
    seed-split <SUBCOMMAND>

FLAGS:
    -h, --help       Prints help information
    -V, --version    Prints version information

SUBCOMMANDS:
    combine    Combine multiple shares into a seed phrase
    help       Prints this message or the help of the given subcommand(s)
    random     Generate a random seed phrase
    split      Split a seed phrase into multiple shares

Generating Seed Phrases

seed-split-random 0.1.0
Generate a random seed phrase

USAGE:
    seed-split random [FLAGS]

FLAGS:
    -h, --help       Prints help information
        --long       If set, generate a 256 bit seed phrase instead
    -V, --version    Prints version information

Splitting Seed Phrases

seed-split-split 0.1.0
Split a seed phrase into multiple shares

USAGE:
    seed-split split --count <count> --threshold <threshold>

FLAGS:
    -h, --help       Prints help information
    -V, --version    Prints version information

OPTIONS:
    -n, --count <count>            The total number of shares
    -t, --threshold <threshold>    The number of shares needed to recreate the seed

The program will then ask for you to enter the seed phrase on the command line.

Combining Shares

seed-split-combine 0.1.0
Combine multiple shares into a seed phrase

USAGE:
    seed-split combine <threshold>

FLAGS:
    -h, --help       Prints help information
    -V, --version    Prints version information

ARGS:
    <threshold>    The number of shares being combined

The program will then ask you for <threshold> shares on the command line.

Implementation

The idea is to use Shamir's Secret Sharing over either GF(2^128) or GF(2^256), depending on whether or not we're using 128 bit or 256 bit seed phrases. Not much else is going on really. The only itch I had to scratch was to encode the shares as seed phrases once again, instead of hex strings like other tools do.