Secret Splitter

What it's for

Split a secret into several shares so that a chosen number of them, together, recover it, while fewer reveal nothing at all. This is Shamir’s secret sharing.

For example, when you want a backup of a password manager’s recovery key that no single person can use: split it into five shares, any three needed, and give them to five people you trust.

How to use it

Type the secret, the number of shares (2 to 20) and how many are needed to recover it (remembered); the shares appear as you type, each with a Copy button, or use Copy all. Each share starts with how many are needed and its number, as in 3-2-…. Tick Show QR codes to print them or scan them with a phone.

To recover the secret, paste at least the needed number of shares into Combine, one per line, in any order.

Example

Paste these two shares into Combine:

2-1-2239c9349ec6f4ce6ab6f845bed7f96fb8a158b6fae2ca0500826095c5b31a201eed9e9305b0e0
2-3-65f1b0e21181cd095821d12b1322c67b21b83a2755d799c7ca79e04c84046ea4fac673eeef15d3

The secret is The spare key is under the blue pot.

Good to know

New random shares are made every time you change anything, and shares from different splits can’t be mixed. A four-byte checksum in each share lets Combine tell a wrong or damaged set from a real secret. Anyone holding enough shares has the secret, so give them to people who won’t get together without good reason. Shares are this tool’s own format, not compatible with other Shamir tools.