ColdCard single seed multi-location backup scheme

Original idea by @KollerTobias and @21isenough.
Documentation of Coldcard backups: https://coldcardwallet.com/docs/backups
The scheme only works if the seed is not locked down to a passphrase: https://coldcardwallet.com/docs/passphrase
In this case the passphrase is not tied to a PIN, but needs to be written in the CC every time the wallet is opened.

The ColdCards should be stored uninitialized, best to be freshly acquired in the tamper resistant package from the manufacturer (https://coldcardwallet.com) to minimize the risk of evil-maid and supply-chain attacks.

Components grouped together by the requirement for a full restore

Full backup 1

  • any BIP39 compatible wallet
  • Seed mnemonic (12/18/24 words)
  • Passphrase

    Full backup 2

  • ColdCard
  • Backupfile (.7z archive on the SD)
  • Backup password (12 words)
  • Passphrase

Packages for a 2-of-3 setup

Location 1

  • Seed mnemonic (12/18/24 words)
  • Backup password (12 words)
  • Backupfile (.7z archive on the SD)

Location 2

  • ColdCard
  • Passphrase (BIP39)
  • Backupfile (.7z archive on the SD)

Location 3

  • ColdCard
  • Passphrase (BIP39)
  • Backup password (12 words)