Recovery phrases
BitTool Signer wallets are standard BIP39 wallets. A phrase created in BitTool Signer restores in any BIP39 wallet that uses the same derivation paths, and a phrase from another wallet can be imported.
Creating a wallet
Creation has four steps:
- Generate. The user names the wallet, chooses 24 words (default) or 12 words, and can add a BIP39 passphrase. The phrase is generated on the device from the system CSPRNG (details).
- Back up. The phrase is shown in one of the backup forms below.
- Check. Every word is hidden, and four positions (five for 18 words or more) are left blank. The user fills the blanks by tapping shuffled words in the right order. A mistake clears the attempt.
- Set the wallet password. It encrypts the phrase on this phone (details).
The public index (addresses and xpubs) is derived and saved before the wallet appears in the list, so pairing works immediately.
Backup forms
Every form starts hidden and appears with one tap. Taking a screenshot, recording the screen or leaving the app hides it again; a screenshot also shows a warning to delete the image.
Words
The 12 or 24 words in a numbered grid: the backup most people should write down.
QR code
A plain-text QR code of the words separated by single spaces, for moving the wallet to another device of your own. Any wallet that imports a phrase from a QR code can read it, and BitTool Signer reads it back with the exact spelling. It never includes the BIP39 passphrase. The app never offers to save, print or share it.
Recovery cards (2 of 3)
The words are split across three cards, so any two cards restore the full phrase but one card alone does not. Positions are laid out in rows of three, and each card leaves out one word per row, shifted by one each row:
card index (0, 1, 2) that leaves out word position p (0-based) = (⌊p / 3⌋ + p mod 3) mod 3
For 12 words:
| Position | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Card 1 | — | ✓ | ✓ | ✓ | ✓ | — | ✓ | — | ✓ | — | ✓ | ✓ |
| Card 2 | ✓ | — | ✓ | — | ✓ | ✓ | ✓ | ✓ | — | ✓ | — | ✓ |
| Card 3 | ✓ | ✓ | — | ✓ | — | ✓ | — | ✓ | ✓ | ✓ | ✓ | — |
The layout depends only on the word count, so cards made at different times, or on another device, always fit together. Each card lists the positions it leaves out.
One card still reveals two thirds of the phrase. What remains to guess is 11 bits per missing word, minus the checksum bits:
| Words | Missing per card | Left to guess |
|---|---|---|
| 12 | 4 | 40 bits: feasible for a determined attacker |
| 15 | 5 | 50 bits |
| 24 | 8 | 80 bits |
For 12- and 15-word phrases the app warns the user to guard each card like the full phrase, or to use 24 words. Recovery cards never include the passphrase.
What is stored
The vault keeps the phrase as canonical words (Unicode NFC) and the BIP39 passphrase exactly as typed. The phrase and passphrase are never written to a plaintext file, never leave the phone, and are not part of any QR code except the explicit recovery phrase QR code above.