Add Shamir's secret sharing protocol

[tupui]

Is your feature request related to a problem? Please describe.

Keeping secrets can be hard and if someone finds the paper wallet, it's compromised.

Describe the solution you'd like

I would like to propose to add a helper function to split the secret key using the Shamir protocol. The PyCryptodome library has an implementation we could leverage.

We could propose the following APIs:

Keypair.secret.to_shamir(n, k)
Keypair.from_shamir(...)

Of course, naming and input parameters should be worked on.

As usual, I am happy to make a PR if wanted 😃

Describe alternatives you've considered

If not suitable in this library, I will add the feature on my higher level Soroban API library.

Additional context

https://pycryptodome.readthedocs.io/en/latest/src/protocol/ss.html

[overcat]

Hi @tupui, this is a very good proposal, but I suggest we build this feature based on python-shamir-mnemonic. I think we can trust the implementation provided by Trezor. We just need to add two functions: generate_shamir_mnemonic_phrase and from_shamir_mnemonic_phrase.

BTW. SLIP-39 was drafted by Trezor, so I hope that when using the same shamir mnemonic, the Python SDK and Trezor wallet can generate consistent keypair.

[overcat]

Keeping secrets can be hard and if someone finds the paper wallet, it's compromised.

In addition, for the existing BIP-39 method, I strongly recommend adding an extra passphrase (aka. 25th word) and memorizing it, which can alleviate this concern to some extent.