Most hardware wallet users protect their seed phrase with a single piece of paper. If that paper is lost, stolen, or destroyed, the funds are gone. Shamir Backup solves this problem by splitting your seed into multiple shares, so that no single point of failure can wipe out your holdings.
Trezor is one of the only hardware wallet manufacturers to support Shamir Backup natively — and it is one of the most powerful security features available to serious crypto holders. This guide explains exactly how it works, how to set it up, and how to use it correctly.
What Is Shamir Secret Sharing?
Shamir Secret Sharing (SSS) is a cryptographic algorithm developed by Adi Shamir in 1979. It works by splitting a secret — in this case, your wallet’s seed — into multiple “shares.” To reconstruct the original secret, you need a minimum number of those shares (the “threshold”).
Example: 2-of-3 Setup
Suppose you create three shares and set the threshold to two:
To recover your wallet, you need any two of these three shares. If one is destroyed in a fire, you still have the other two. If one is stolen, the thief cannot access your funds without a second share. The redundancy and security are both dramatically improved over a single seed phrase.
How Trezor Implements Shamir Backup (SLIP39)
Trezor’s Shamir Backup implementation follows the SLIP39 standard (also known as SSSS — Shamir’s Secret Sharing Scheme for Bitcoin). Key features:
SLIP39 vs BIP-39
| Feature | BIP-39 (Standard) | SLIP39 (Shamir) |
|---|---|---|
| Number of words | 12 or 24 | 20 or 33 per share |
| Number of backups | 1 | Multiple (configurable) |
| Single point of failure | Yes | No (with 2+ shares) |
| Compatibility | Universal | Trezor and SLIP39-compatible wallets only |
| Complexity | Simple | Moderate |
| Recovery flexibility | None | High (multiple share combinations) |
Important: SLIP39 shares are not compatible with wallets that use BIP-39. If you set up Shamir Backup, you can only recover your wallet on a Trezor device or other SLIP39-compatible tools. This is a trade-off worth understanding before you commit.
Supported Trezor Models
Shamir Backup is supported on:
It is not available on the Trezor Model One due to hardware limitations.
Choosing Your Share Threshold
The most common configurations and when to use each:
| Configuration | Best For | Trade-off |
|---|---|---|
| 1-of-1 | No real advantage over standard backup | N/A |
| 2-of-3 | Most individuals — good balance of security and redundancy | Three separate storage locations needed |
| 3-of-5 | High-value holdings, families, businesses | More complexity, more storage locations |
| 2-of-2 | Two-person joint accounts or strict dual control | Both shares must be available to recover |
For most individual users, 2-of-3 is the sweet spot. You gain strong redundancy (one share can be lost) while limiting the risk of any single share being used to steal funds.
Setting Up Shamir Backup: Step-by-Step
Prerequisites
- A Trezor Safe 3, Safe 5, or Model T
- Trezor Suite installed on your computer
- Multiple pieces of paper or metal backup media (one per share)
- A secure, distraction-free environment
Step 1: Open Trezor Suite and Start Device Setup
If setting up a new device, the Shamir Backup option will appear during initial setup. If you already have a device and want to switch to Shamir, you will need to wipe the device first (make sure you already have your current seed safely backed up).
Step 2: Select “Shamir Backup” When Prompted
During the “Create new wallet” flow, Trezor Suite will ask you to choose between Standard Seed Backup and Shamir Backup. Select Shamir Backup.
Step 3: Choose Your Share Count
Enter the total number of shares you want to create (e.g., 3).
Step 4: Choose Your Threshold
Enter the minimum number of shares required to recover (e.g., 2 for a 2-of-3 setup).
Step 5: Write Down Each Share
The device will display share 1 word by word on screen. Write down every word in order on a piece of paper. When prompted, verify the words by entering them on the device.
Repeat this process for each share. Each share is a different set of 20 words — do not mix them up.
Step 6: Label and Store Each Share Separately
Label each piece of paper clearly:
- “Shamir Share 1 of 3 — [Your Name] — [Date]”
- “Shamir Share 2 of 3 — [Your Name] — [Date]”
- And so on.
Store each share in a different physical location. Never store two shares in the same place.
Step 7: Set Your PIN
Follow the standard Trezor PIN setup process. The PIN adds a layer of protection if a share is discovered alongside the device.
Advanced: Group Sharing
Trezor’s SLIP39 implementation supports group sharing for institutional or family setups. This allows you to define multiple groups of shares, each with their own threshold.
Example: 2-of-3 Groups
- Group A: 2-of-3 shares (your personal copies)
- Group B: 2-of-3 shares (trusted family member holds these)
- Recovery requires completing at least one full group (2 shares from Group A OR 2 shares from Group B)
Group sharing is powerful but complex. It is best suited for:
- Family or business accounts with multiple trusted parties
- Geographically distributed backup strategies
- Estate planning where heirs need recovery access
Storing Your Shamir Shares Securely
Recommended Storage Options
| Storage Type | Security Level | Notes |
|---|---|---|
| Home fireproof safe | Good | Fast access, physical theft risk |
| Bank safety deposit box | Very Good | Slow access, resistant to house fires/theft |
| Trusted family member | Good | Depends on relationship trust level |
| Solicitor / attorney | Very Good | Professional obligation to safeguard |
| Geographic secondary location | Good | Second home, workplace |
What Not To Do
Metal Backup Plates
For maximum durability, consider engraving or stamping your Shamir shares onto stainless steel plates. Products like Cryptosteel or Bilodeau are specifically designed for this. Metal plates survive fires up to 1400°C and are waterproof.
Recovering Your Wallet with Shamir Shares
If you need to restore your wallet — on a new Trezor or after a wipe — the recovery process differs from standard seed recovery.
Step-by-Step Recovery
- Connect the new or wiped Trezor device and open Trezor Suite
- Select “Recover Wallet” instead of “Create New Wallet”
- Choose “Shamir Backup (SLIP39)” as the recovery method
- Enter the first share word by word using the device’s randomised keyboard
- The device will prompt for additional shares until the threshold is met
- Once the threshold is reached, the wallet is fully restored
Note: The shares can be entered in any order. Share 1, 2, or 3 — it makes no difference which you enter first.
Advantages of Shamir Over Standard 24-Word Backup
| Advantage | Detail |
|---|---|
| No single point of failure | One share alone cannot recover the wallet |
| Redundancy | A share can be lost without losing access |
| Flexible trust model | Different people can hold different shares |
| Disaster resilience | Geographically distributed against fires/floods |
| Estate planning | Heirs can be given shares with controlled access |
Disadvantages and Limitations
Who Should Use Shamir Backup?
Shamir Backup is best suited for:
It may be overkill for:
- Small amounts (under $5,000) where simplicity is more important
- Users who are not confident they can correctly manage multiple storage locations
Frequently Asked Questions
What happens if I lose one Shamir share?
If you have a 2-of-3 setup and lose one share, your funds are still completely safe. You still have two shares, which meets the recovery threshold. You should create a new Shamir Backup as soon as possible to restore your three-share redundancy.
Can I use Shamir Backup shares with a non-Trezor wallet?
Not easily. SLIP39 is an open standard, but most wallets only support BIP-39 seeds. Some SLIP39-compatible tools exist (like the trezor/python-shamir-mnemonic library), but practical recovery outside of a Trezor device requires technical knowledge. This is an important limitation to understand before choosing Shamir over standard backup.
How many words are in each Shamir share?
Each SLIP39 share consists of 20 words (for a 128-bit seed) or 33 words (for a 256-bit seed). These are different from the 12 or 24-word BIP-39 seeds used for standard backups.
Can I convert an existing Trezor wallet to Shamir Backup?
Not directly in place. To switch to Shamir Backup, you would need to wipe the device and set up a new wallet with Shamir enabled. This means migrating your funds to new addresses, as the Shamir backup generates a new seed. Always move your funds before wiping.
Is Shamir Backup available on the Trezor Model One?
No. Shamir Backup requires a Trezor Model T, Safe 3, or Safe 5. The Model One’s hardware cannot support SLIP39.
What is the maximum number of shares I can create?
Trezor’s SLIP39 implementation supports up to 16 total shares. In practice, most users choose between 3 and 5.
Does using Shamir Backup change which coins are supported?
No. Coin support is independent of the backup method. Shamir Backup affects how your seed is stored and recovered, not which assets can be held on the device.
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