0c77cc4534
* fix: correct reprint threshold display and de-duplicate the formula (F5) Print.vue recomputed the recovery threshold as floor(total/2)+2 and stored the *total* in a field misleadingly named `requiredShards`. The reprint sheets therefore overstated how many more QR codes are needed (e.g. total=5 showed "need 4" instead of the correct 3) — misleading during recovery, though the QR payloads themselves were always untouched. Root cause: the threshold policy was duplicated. Share.vue computes floor(total/2)+1; Print.vue re-implemented it and drifted. Extract a single `defaultThreshold()` helper (src/util/shards.ts) and use it in both, so they can never disagree again. Rename Print.vue's field to `totalShards` to match what it actually holds. Add unit tests for the helper, including the exact F5 case (total=5 -> 3) and a strict-majority invariant across the whole 3..255 UI range. * fix: reject fractional shard counts, clamp the remaining-code count Review follow-ups on the reprint view. `<input type="number">` only constrains the spinner, not the value: typing "3.5" (or clearing the box, which `v-model.number` leaves as "") sailed through the old `>= 3 && <= 255` check and reached defaultThreshold(), producing fractional totals and remaining counts. Add `step="1"` for the spinner and gate on a shared `isValidShardCount()` predicate that also requires a whole number, so the input and the threshold policy keep agreeing about what a shard count is. `needMoreShards` compared with `!==`, so scanning more codes than announced kept the scanner open and drove `remainingCodes` negative. Compare with `<` and clamp the remainder at 0. `threshold` returned 0 for "nothing entered yet", a valid-looking value that could reach ShardInfo's required-shards prop. Return `undefined` instead and guard the consuming block on it, making the not-yet-entered state explicit. The `threshold` and validation paths are covered by shards.spec.ts; the scanner-overshoot clamp is not, as the repo has no component-test harness yet. * fix: apply the same shard-count validation to the generator Share.vue's shard-count input had the defect Copilot flagged on Print.vue's: no `step`, no integer check, and `totalShards` fed straight into crypto.share() — a fractional count surfaced as an opaque secrets.js error routed through the generic error hub, and an emptied box passed "" through. Reuse `isValidShardCount()` and gate the generate button on it, matching the existing `secretTooLong` pattern (disabled button plus an inline error span), so both shard-count inputs now agree on what a shard count is. * fix: stop rendering a threshold derived from an invalid shard count Gating the generate button left the sentence above it still interpolating defaultThreshold(totalShards) for values that had just been rejected: an emptied field coerces to 0 and renders "Will require any 1 shards", and 3.5 renders 2. Give Share.vue's `requiredShards` the same contract as Print.vue's `threshold` — `undefined` unless the count is usable — show an em dash in the sentence, and guard both the generated-shards block and crypto.share() on it. Also strengthen the threshold invariant test. Asserting only `defaultThreshold(n) > n / 2` does not pin the policy: floor(n/2)+2, the very formula this branch removed, satisfies it for every even n. Assert the smallest strict majority instead, which floor(n/2)+1 alone satisfies. |
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Banana Split 🍌 · 
Banana Split makes your paper backups more resilient and secure using Shamir’s secret sharing.
It splits your secret (e.g., paper backup) into N pieces, but only requires a majority of those pieces (N/2+1) to recover your secret.
Why Banana Split?
There’s a few problems with normal paper backups: If you have the whole paper backup somewhere, you’re vulnerable to someone finding it and stealing it—without you ever knowing they did (e.g., they can just take a photo of it). If you split your paper backup into two, what happens if one of those pieces goes missing?
For example:
You use Banana Split to split your paper backup into 5 pieces. You then give 5 friends a piece. It only takes 3 of those friends to come together to retrieve the paper backup. If 2 of your friends end up losing their piece, it’s okay. And if 2 of your friends collude and try to retrieve your backup, they won’t be able to. That is to say:
Any 3 friends will know everything; any 2 friends will know nothing.
Usage
How do you make a Banana Split?
- Save the Banana Split HTML page and open it in offline mode.
- Type your secret into Banana Split. Your secret will be encrypted with an auto-generated passphrase and split it into the number of QR codes you specify.
- Print out your QR codes.
- Write the passphrase by hand on every sheet. Doing this by hand protects against an attacker intercepting things you’re sending to the printer.
How do you retrieve a Banana Split?
Recovery can be done on any device with a webcam.
- Save the Banana Split HTML page and open it in offline mode.
- Using your webcam, scan in a majority of your QR code printouts (e.g., if you had 7 printouts, you’ll need 4).
- Enter your passphrase.
- Viola! Your secret is restored.
⚠️ Important
Work local and offline
Banana Split is a self-contained HTML page. To ensure your precious data is never sent outside, it only works when opened from your local hard drive while your browser is in Offline mode.
Without the passphrase, you won’t be able to retrieve your secret
To retrieve your secret, you’ll need to have a majority of the printouts and know the passphrase. This is why it is critical for you to write the passphrase on every printout.
Keep the HTML document
This HTML page is a fully self-contained application under GPLv3 license. Please feel free to copy and share it with anyone you want to use it. The more copies out there, the less likely it will be compromised or taken down.
Development
Project setup
yarn install
Compiles and hot-reloads for development
yarn run serve
Compiles and minifies for production
yarn run build
Run unit tests
yarn run test:unit
Run end-to-end UI tests
yarn run test:e2e
Lints and fixes files
yarn run lint