Banana Split

Banana Split is an Android application from mezinster that divides a secret into several shards using Shamir's Secret Sharing. The scheme splits a value into a chosen number of parts with a threshold, so that any subset of that size can reconstruct the original while smaller subsets reveal nothing about it. Each shard is rendered as a QR code, which can be printed or photographed and stored in separate places.

Common uses include recovery material such as passphrases, seed phrases or key backups, where keeping a single written copy concentrates the risk of loss. Reconstruction works the other way around: enough shards are scanned back in, and the application recombines them into the original secret.

The application is published under GPL-3.0-only. It runs on Android only, and the usefulness of the approach depends on the shards being kept apart, since the threshold assumption is what the whole scheme relies on.