BIP-39 Seed Phrases are often protected by a Passphrase, to partially
offset their insecurity.  This often makes the Seed unrecoverable,
because the Passphrase can be so easily lost or forgotten.

SLIP-39 Mnemonic Card Groups are *much* more reliable (to recover) and
secure (against accidental disclosure); a Passphrase is *not*
recommended.  Leave it empty!


1 BIP-39 Passphrase
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  Since anyone who sees a BIP-39 phrase can immediately attempt to
  recover the Seed, it is often considered necessary to use a
  Passphrase.

  It is estimated that 20%+ of all Cryptocurrency has been lost, often
  because the BIP-39 Mnemonic is available but the Passphrase has been
  lost.


1.1 Safely Using BIP-39 Passphrases
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  Once you Backup your BIP-39 Seed Phrase to a set of SLIP-39 Mnemonic
  Card Groups, you *must* also arrange to secure and recover any BIP-39
  Passphrase(s).  Remember; you can have multiple Passphrases, to
  produce several sets of Cryptocurrency HD wallet accounts from the
  same BIP-39 Seed Phrase.

  Make certain that each Passphrase is made available to each intended
  recipient, and also in at least one additional location (eg. with
  someone else who will be at your funeral).


1.1.1 Backup Full 512-bit BIP-39 Seed *including* Passphrase!
╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌

  If you've *already* produced a BIP-39 Seed Phrase and a complex
  Passphrase, and have already funded or distributed the derived HD
  Wallet accounts, you can *still* back it up, securely and reliably
  with SLIP-39 – without requiring the Passphrase to be remembered by
  the recipient!

  Use the Pro controls and select "BIP-39 Seed" + "Passphrase" to fully
  decrypt your BIP-39 Seed Phrase.  Then, produce 59-word SLIP-39
  recovery cards encoding the full, decrypted 512-bit Seed.

  These will *not* be compatible with standard BIP-39 nor SLIP-39
  Hardware Wallets!  (Don't blame me – you elected to create an insecure
  and unreliable BIP-39 Seed Phrase + Passphrase, instead of SLIP-39
  Mnemonic Cards! ;)

  Your heirs or business partners will need to use a fully standards
  compliant SLIP-39 recovery program (like this SLIP-39 App, or
  [python-shamir-mnemonic on Github] ) to enter the large (but
  standards-compliant!) 59 word Mnemonics, and then generate Paper
  Wallets for each derived HD Wallet account they want to access.  But,
  they *will* be able to recover your cryptocurrency accounts, *without*
  needing to recover the original BIP-39 Seed Phrase or Passphrase!


[python-shamir-mnemonic on Github]
<https://github.com/trezor/python-shamir-mnemonic>


2 SLIP-39 Passphrase
════════════════════

  If you use SLIP-39 Mnemonic Card Groups, it is usually not necessary
  to use a Passphrase.

  Since SLIP-39's security is so much greater (chance of accidentally
  disclosing your Seed is so low compared to BIP-39), no hardware wallet
  vendor has implemented SLIP-39 recovery Passphrase.


2.1 Hardware Wallet Doesn't Support Passphrase
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  The Trezor "Model T" doesn't presently support using a Passphrase on
  SLIP-39 recovery.  So, if you supply one here, you will not be able to
  use it when recovering your SLIP-39 Mnemonics on your Trezor "Model
  T".


2.1.1 Use Trezor's "Hidden Wallets" Instead
╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌

  You can provide as many "Hidden Wallets" on your Trezor device as you
  wish, by entering a passphrase to switch between them.

  This works regardless of whether you recovered your Hardware Wallet
  from BIP-39 or SLIP-39.
