Seed XOR

Seed XOR is a way to split a BIP39 recovery phrase into two or more parts, each of which is itself a valid recovery phrase of the same length. It was introduced by Coinkite for the Coldcard and is a feature of that product line, not a Bitcoin standard.

The split uses the XOR operation on the seed's underlying bits. Combining all parts with XOR again returns the original seed. Every part is required: there is no threshold such as 2 of 3, so losing one part means losing the wallet unless the original phrase is also backed up.

Because each part looks and works like an ordinary seed phrase, it can be stamped on standard metal backups, and it can hold a small wallet of its own. Someone who finds one part cannot tell that it belongs to a split, and learns nothing about the real seed.

There is no error message for a wrong combination. A missing or incorrect part simply produces a different, empty wallet, so it pays to record how many parts exist and to note the wallet fingerprint of the combined seed. The XOR itself can be done on paper, so the parts can be combined without Coldcard hardware, although the final checksum word needs a computer to recalculate.