Title: Shamir seed backup: SLIP-39 (Trezor) vs splitting a BIP39 seed into encrypted shares?
I’m building an open-source inheritance tool (vault.js) that runs offline on Tails. It takes a BIP39 seed, splits it 3-of-5 with Shamir, then encrypts each share with Argon2id + AES-256-GCM under a passphrase.
Trezor uses SLIP-39 instead, where the shares are word lists and the wallet itself rebuilds the seed.
What are the security trade-offs between the two approaches?
- Is encrypting each share worth it, or does it add a new single point of failure (the passphrase)?
- Does splitting a BIP39 seed carry known risks that SLIP-39 was designed to avoid?
- For heirs who aren’t technical, which is safer to recover from in 20 years?
Code and threat model: https://github.com/Ashworth78/btcguardianshq
