Keeping half of your words in one place and half in another feels like a clever way to protect them. It is a common idea, and it does more harm than good. This guide is part of our seed phrase backup guide.
Why it seems like a good idea
If a burglar finds half of your phrase, they cannot use it, or so the thinking goes. And you do not have to trust any one location with everything.
Why it weakens your security
Each word of a BIP39 phrase carries 11 bits. Revealing some of them takes that strength away:
| Your phrase | Words a thief finds | Unknown strength | Result |
|---|---|---|---|
| 12 words | 6 | About 62 bits | Within reach of well-funded attackers |
| 12 words | 8 | About 40 bits | Easy for a modern computer |
| 24 words | 12 | About 124 bits | Still strong, but you have lost half |
With a strong 12-word phrase, a thief who finds half of it has a real chance of finishing the job, using specialized hardware.
Why it makes loss more likely
Now you need both halves to restore. Lose either one, in a fire, flood or clear-out, and everything is gone. You have turned one point of failure into two. Each half also has no spare.
To avoid that, you would need more copies, which brings back the original problem.
What about clever overlaps?
Some people split their words across three sheets, so that any two can rebuild the phrase. Each sheet still reveals two-thirds of the words, leaving much weaker protection than a real scheme.
What to do instead
| Goal | Better tool |
|---|---|
| No single sheet is enough | Shamir backup |
| No single key can spend | Multisig |
| A found sheet is not enough | Passphrase |
| Surviving a disaster | Two full copies in separate places |
These were designed for the job. Shamir, for instance, is built so that fewer than the required number of shares reveal nothing. Our guide to Shamir vs multisig compares them.