Trezor now defaults to the Shamir Backup Scheme on its Safe product line, which raises a practical question for anyone setting up a new device: is a single-share Shamir backup actually better than the traditional BIP-39 seed, or is it a change worth overriding?
What Shamir backup actually is
Shamir Secret Sharing, standardized as SLIP-0039, is a cryptographic method that splits a wallet backup into multiple shards, configurable so that a chosen number of shares out of a total set (an "x of n" scheme) is required to recover the wallet. On Trezor Safe devices this shows up as a 20-word seed backup instead of the familiar 12 or 24-word BIP-39 phrase.
It is worth being precise about what this does and does not do. Shamir is a recovery scheme for a single key, splitting one secret into shares that reconstruct it. It is not multisig, where multiple independent keys must each sign a transaction. Electrum’s multisig wallet scheme works with any Trezor device and covers that use case instead. Electrum can restore a wallet from Shamir shares, but it cannot sign transactions for a Shamir wallet on a Trezor, an important limitation to know about before committing to one setup or the other.
The case against Shamir for most users
- No added security for a single share: both schemes rely on 256 bits of entropy, so a single-share Shamir backup means managing more words (20 versus 12 or 24) without any additional cryptographic strength.
- Recovery only, not multisig: Shamir cannot be used to let multiple people co-sign a transaction.
- Limited software support: no wallet client currently supports signing transactions for a Shamir wallet on a Trezor, even where restoration is supported.
- Locked into one ecosystem: neither Ledger nor Coldcard supports Shamir, and there has been little movement toward adopting it elsewhere. Coldcard uses a different splitting scheme, SSKR, instead.
The case for Shamir
The strongest argument for Shamir is future flexibility. A single-share backup can later be expanded into a genuine multi-share configuration without regenerating the seed or moving coins, keeping a personal wallet as one share while adding shares for a shared business wallet with partners, for example. The caveat is that securing existing coins under a multi-share configuration still requires transferring funds to new addresses derived from that configuration, so the flexibility is real but not entirely free.
Shamir is also the only multi-signature-adjacent scheme fully supported natively in Trezor Suite, which makes it a convenient default for anyone already committed to that ecosystem. Trezor now also sells multi-share metal seed backups supporting up to 16 shares, making physical backup of a multi-share setup considerably more practical than it used to be.
A single-share Shamir backup does not add security over BIP-39. Its value is entirely in the option it preserves to move to a genuine multi-share setup later without starting over.
The practical recommendation
For anyone who values simplicity and the broadest possible wallet compatibility, BIP-39 remains the standard choice for a single-share backup. For anyone planning to move toward a multi-share setup down the line, comfortable being anchored to the Trezor ecosystem, and not reliant on Electrum’s more advanced transaction features, Shamir is a reasonable and forward-looking choice.