Safety numbers
Last updated October 2, 2026
What is a safety number?
Every MoatKey account has a sharing key. A safety number is a short fingerprint of that key: 30 digits in six groups of five.
When you add someone to a shared Castle, MoatKey seals the Castle's key to their sharing key. If someone in between (even MoatKey's own server) slipped in a different key, your number for them would not match the number on their screen. Comparing the two numbers proves you're sharing with the real person.
How to compare
- Get in touch with the person another way: a phone or video call, or in person. Don't use an email or message that might come from someone else.
- Ask them to read their number to you.
- If they just accepted, they see Your safety number right under the invitation.
- Members of a Castle can open Members and choose My safety number, under Details.
- On your side, open Members and find them. People who just accepted are under People who accepted. For people already in the Castle, choose Safety number.
- If every digit matches, choose Numbers match — add them (for someone who accepted) or Numbers match (for someone already in the Castle).
Once you've compared on a device, MoatKey marks them Verified there.
What the labels mean
- Verified: you compared their number on this device.
- Not verified: you haven't compared yet.
- Compare new number: their number changed for a known reason (for example, they switched to quantum-safe sharing). Compare it once more.
- Safety number changed: their key is different from the one this device saw before.
- Not set up yet: they haven't finished setting up their account.
If a safety number changes
Sharing keys don't change when someone reinstalls MoatKey or gets a new phone. A Safety number changed warning may mean someone in between swapped their key. Call them and compare the new number before you trust it.
If MoatKey warns that the server is showing others a different key for you, don't share anything in that Castle until you've contacted support at support@g3nosystems.com.