SLIP39: An Easy and Powerful Way to Secure Your Wallet Backup

When you hold bitcoin in self-custody, your backup is the master key to your wallet. It represents all your private keys and allows you to restore access to your funds if your device is lost, damaged, or inaccessible. Most wallets today use the BIP39 standard, which generates a 12 or 24-word seed phrase to secure your funds.

While effective, relying on a single seed phrase can feel risky. If it’s lost, you lose access to your funds forever; if it’s stolen, someone else could take control of your assets. The question is, how do you improve this? That’s where SLIP39 comes in.

SLIP39 offers a more flexible and secure solution by allowing you to split your backup into multiple parts, or shares, ensuring that even if one part is lost or compromised, your funds remain safe.

What is SLIP39?

SLIP39 is based on Shamir’s Secret Sharing (SSS), a cryptographic method developed by Adi Shamir in 1979. As an open-source standard designed to improve the security and flexibility of seed phrases, SLIP39 allows you to split a wallet backup into multiple parts, called shares, which can then be distributed and securely stored in different locations. SLIP39 ensures that a specific number of shares, or a threshold, is required to recover the wallet, adding an extra layer of protection.

For example, you might split your backup into three shares and set a threshold of two. This means you only need two of the three shares to recover your wallet, which provides extra redundancy and improves security. Even if one share is lost or compromised, your wallet remains recoverable as long as you still have enough shares to meet the threshold. Additionally, if a share is stolen, the attacker cannot access your wallet unless they gather enough shares to meet the recovery threshold.

Why Not Just Split Your Existing Seed Phrase?

Simply dividing your BIP39 seed phrase into parts doesn’t provide the same level of security. If an attacker finds even a few parts, they’re already much closer to reconstructing your full seed phrase. For example, splitting a 24-word seed into two halves of 12 words each makes it much easier for someone to guess the rest. Once they have one part, the task of guessing or brute-forcing the remaining part becomes far easier.

In contrast, SLIP39 uses cryptography to ensure that no single part—or combination of too few parts—reveals anything about the seed phrase. Even if an attacker finds a part of your SLIP39 backup, they can’t use it to recover your wallet unless they have the minimum number of parts required for recovery. This makes SLIP39 far more secure.

How SLIP39 Works

SLIP39 allows you to split your wallet backup into multiple parts, or shares, and set a recovery threshold, adding flexibility and security to your backup process. You can create up to 16 shares, and the threshold can be set to any number, as long as it is smaller than or equal to the total number of shares.

Let’s say you decide to split your seed into three shares and set a recovery threshold of two. You could distribute the shares like this:

Store one share at home.
Keep one share at your office.
Give one share to a trusted friend or family member.

Even if one of these shares is lost or compromised, you can still recover your wallet with the remaining two. This ensures that your backup is protected against accidents, theft, or other unforeseen events, removing the risk of a single point of failure.

It’s much harder for a thief to steal from several places than to compromise a single word list.

Everyone’s situation is different. Before setting up a shared backup, it’s important to consider factors like your living arrangements, people you trust, and where you can securely store your shares. Plan a backup strategy that works for your specific needs.

What is the difference between SLIP39 and Multisig?

Multisig (multi-signature) wallets require multiple signatures from different wallets to authorize transactions, but SLIP39 focuses on securing the backup of a single wallet. It lets you split and distribute that backup securely, so even if one part is lost, your wallet can still be restored. SLIP39 provides flexibility and redundancy at the backup level, whereas multisig operates at the transaction approval level.

Difference between Shamir Secret Sharing and Multisig from the Codex32 Booklet

SLIP39 Adoption in Wallets

SLIP39 was developed by SatoshiLabs, the company behind Trezor, and also the creators of BIP39, the widely used standard for 12 and 24-word recovery seed phrases. As an open-source standard, SLIP39 is freely available for developers to integrate into their wallets. This openness has led to broader adoption, with hardware and software wallets incorporating SLIP39 to enhance recovery options for users.

In 2017, Trezor implemented SLIP39 as Shamir Backup, and Keystone followed in 2021 by adding SLIP39 to their hardware wallets. In 2024, Trezor devices made SLIP39 single-share and multi-share backups a default option, allowing users to initially create a single seed phrase (single-share) and later upgrade to multi-share.

Many software wallets now also support SLIP39, offering users more recovery options, which are especially useful in emergencies when they might be unable to access their hardware devices.

SLIP39 for Inheritance Planning

SLIP39’s flexibility makes it an excellent option for inheritance planning. You can distribute shares among trusted family members or other secure locations (e.g., vaults or lawyers). By setting a recovery threshold (e.g., 3-of-5), you can ensure that your bitcoin is accessible to your heirs without relying on a single person or location. This prevents premature access but guarantees that your assets won’t be lost.

Tips for Using SLIP39

Here are some practical tips to help you get the most out of SLIP39:

Distribute your shares securely: Keep shares in different secure locations or with trusted individuals to minimize the risk of losing all your backups at once.
Set a practical threshold: A common configuration is 2-of-3 or 3-of-5, which ensures your wallet remains recoverable even if some shares are lost or compromised.
Consider backing up one or more shares on metal: Storing a share on metal ensures it’s protected against fire, water, and other potential disasters that could damage paper backups.
Never store shares digitally: Avoid storing shares on digital devices, as this increases the risk of hacking or unauthorized access. Stick to physical storage options, like paper or metal.
Periodically test your recovery process: Practice recovering your wallet from time to time to ensure your shares work and are easily accessible. This helps avoid surprises or stress when you need to recover your wallet.

Conclusion

SLIP39 provides a secure and flexible way to protect your wallet backup. By splitting your wallet’s master key into multiple shares with a recovery threshold, it reduces the risk of a single point of failure and ensures your funds stay safe and accessible.

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