An Overview of Using a Shamir Backup With the Trezor Model T

A Shamir Backup is a security feature available on the Trezor Model T hardware wallet. It addresses the risks associated with protecting your recovery seed, which is crucial for accessing your digital assets. With Shamir Backup, you create multiple recovery shares, each containing a portion of the mnemonic seed. By setting a threshold, which determines the number of shares required to recover your wallet, you enhance the security of your backup.
Here's an overview of using Shamir Backup with the Trezor Model T:
1. Shamir Backup Process: Instead of a single recovery seed, you generate multiple recovery shares. Each share consists of 20 or 33 English words representing a part of the mnemonic seed. Combining the required number of shares will produce the master secret or seed needed to recover your wallet.
2. Setting up Shamir Backup: Trezor Suite can automatically set up your device with Shamir Backup using twenty-word shares, providing 128-bit strength. If desired, you can adjust the strength to 33-word shares, offering 256-bit strength during the setup process. You choose the number of shares to be generated, ranging from one to a maximum of 16.
3. Recovery Share Example: Let's consider a complete Shamir backup with three recovery shares. The first three words are the same in all three shares. The first and second words identify the shares and are consistent across all shares. The third word encodes the group index used in Shamir backup systems.
4. Threshold: The threshold is the predetermined number of shares needed to access your wallet. Any individual share can be used as long as the threshold is met. The order of the shares is not important when creating a new wallet, and you can decide the threshold based on your needs.
5. Recovery with Threshold: For example, with a Shamir backup of three shares and a threshold of two of three, any two shares can reconstruct the wallet. Even if one share is lost, the private keys can still be recovered. If thieves steal one share, they won't be able to recover the wallet with a single share.
6. Comparison to Single Recovery Seed Backup: Shamir Backup differs from single recovery seed backup in several aspects. Shamir Backup allows you to generate up to 16 recovery shares of 20 or 33 words, while single recovery seeds consist of 12, 18, or 24 words. Additionally, Shamir Backup uses a different word list compared to BIP39 recovery seeds, introducing unique words.
7. Lost or Stolen Shares: If some shares get lost or stolen, Shamir Backup provides a significant advantage. As long as the compromised shares do not reach the required threshold, individual shares do not reveal any information about the shared secret.
8. Passphrase and Hidden Wallets: You can use a passphrase to create hidden wallets on a Trezor Model T with Shamir Backup, adding an extra layer of security to your wallet.
9. Converting Existing Trezor Wallet: Currently, it is not possible to directly convert an existing recovery seed into a Shamir