Entropy check: how Trezor verifies your wallet is truly random

When setting up your Trezor, the entropy check ensures your wallet backup is generated randomly.

Your wallet is created from random data (entropy) contributed by both your Trezor and Trezor Suite. The entropy check lets Trezor Suite verify that the device really combined both contributions. This means your wallet stays unpredictable even if the device's own source of randomness were secretly rigged.

If the check fails, Trezor Suite blocks access to the wallet to prevent you from losing your funds.

While rare, some users who purchase Trezor from unauthorized resellers may unknowingly receive a device that does not produce truly random seeds. The entropy check mitigates this risk. If a device is found to handle randomness incorrectly, Trezor Suite will block access to the wallet.

How does the entropy check work?

During setup, Trezor Suite asks the device to create a wallet several times in a row. Each wallet except the last one is checked and then discarded. The last wallet in the sequence becomes your actual wallet.

Entropy check procedure

1. Commitment

• Before Trezor Suite sends its random data, the device commits to its own random data. This prevents the device from changing its contribution after seeing what Trezor Suite sent.

1. Wallet creation

   • When you set up your Trezor, it generates a wallet using random data (entropy) from both Trezor and Trezor Suite to ensure unpredictability.

2. Reading the wallet's fingerprint

   • Trezor Suite asks the device for the wallet's XPUBs (extended public keys), which uniquely identify the wallet without exposing any private keys.

3. Reveal and verification

   • Trezor Suite then asks the device to discard the wallet and reveal the random data it used. Trezor Suite checks that the revealed data matches the earlier commitment, recreates the wallet on the computer from the two pieces of random data, and verifies that it produces exactly the same XPUBs the device reported. Because the revealed wallet is now fully known to the computer, it is thrown away and never used. No funds are ever at risk.

4. Comparison

   • If the XPUBs match, the device demonstrably built the wallet from both sources of randomness, exactly as it should.
   • If they don’t match, the device may be counterfeit or compromised.

5. Random checks

   • Trezor Suite repeats this process a random number of times, from 1 to 5. The device cannot know which round will be the last one, so it cannot behave honestly during the checks and cheat only on the wallet you keep.

6. Wallet is verified

   • The final wallet in the sequence becomes your wallet. Its random data is never revealed, so it remains secret and secure. Trezor Suite remembers this wallet's XPUBs and checks that they stay the same every time you connect your Trezor. This prevents a malicious device from silently swapping your wallet later.

7. What happens if it fails?

   • If any check fails, Trezor Suite blocks access and prevents you from using the wallet.
   • If the entropy check fails, you will see the following popup in Trezor Suite. Press "Contact Trezor Support" and reach out immediately if this happens.

Why would the entropy check fail?

If the entropy check fails, it means the device did not build the wallet from the combined random data the way it claims to. A genuine Trezor never fails this check. Cryptographic security depends on your wallet being unpredictable. A device that ignores the random data from Trezor Suite could generate wallets that look normal but are secretly predictable, allowing whoever tampered with the device to recreate your wallet and steal your funds. A failed entropy check therefore indicates that the device is counterfeit or compromised.

What should I do if the entropy check fails?

If the entropy check fails, contact us immediately via:

• The prompt in Trezor Suite
• Our Chatbot Hal

A Trezor support agent will reach out as soon as possible with the next steps.