Shamir backup usually means SLIP-39. It splits a wallet’s master secret into shares and sets a recovery threshold. A 2-of-3 setup, for example, creates three shares and requires any two of them to recover the wallet. One share alone reveals no usable secret.
This solves a real problem: no single place or custodian holds the whole secret, while a limited number of shares may be lost. It can suit a family, partnership, or institution with clear roles and a maintained recovery process. This site does not make it the default for individuals.
The recovery rules are harder to hand down
A conventional backup has one rule: find one complete seed phrase, then add the passphrase.
With SLIP-39, the person recovering the wallet may also need to know the total share count, the threshold, whether groups were used, each group threshold, and which shares belong to the same backup. Years later, that person may be a family member who never learned the setup.
There are more words to manage
The default plan on this site copies the same 12 words two or three times. A 128-bit SLIP-39 share is normally 20 words. A 2-of-3 setup stores 60 words in total and requires at least 40 correctly preserved words for recovery. More material creates more opportunities for transcription errors, mix-ups, and loss.
The specification also notes that converting an existing BIP-39 wallet produces 59 words per SLIP-39 share. Read the SLIP-39 specification
Falling below the threshold is final
A 2-of-3 setup tolerates one lost share. If only one remains, however, that share cannot recover anything. It is easy to mistake “three shares” for “three backups,” even though none of the shares is a complete backup by itself.
The threshold protects against disclosure of one share, but it also makes recovery depend on locating and combining several items. Trezor likewise states that recovery becomes impossible once the available shares fall below the threshold. Read the Trezor SLIP-39 FAQ
Compatibility is narrower than BIP-39
SLIP-39 does not cut a 12-word BIP-39 phrase into pieces. It uses its own word list and encoding. The two standards are mostly incompatible, and SLIP-39 shares cannot simply be converted back into a conventional BIP-39 phrase.
Recovery therefore requires a device or application that supports SLIP-39. If a device disappears, software changes, or an heir takes over, there are fewer recovery tools to choose from.
A security plan must be rehearsed
A recovery drill must confirm not only that each share is readable, but also that enough shares can be found, that they belong to the same set, that the threshold is understood, and that compatible recovery software remains available. A complex plan that has never been rehearsed is secure only on paper.
The default on this site
Hand-copy the complete 12-word seed phrase two or three times and store the copies in separate places. Use a passphrase and keep it apart from the seed phrase.
Every seed copy can take part in recovery by itself, so any surviving copy remains useful. The passphrase reduces the risk created by accidental exposure of one seed copy. For most individuals, this is a better balance of security, recoverability, and complexity.
SLIP-39 is not unsafe. Its extra complexity becomes worthwhile when you truly need shared custody, cannot allow any one person to hold the whole secret, and can maintain and rehearse the recovery process over time.
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