Seed Phrase Management

Authored by:

Piña

Coinspect

Isaac Patka

SEAL | Shield3

Geoffrey Arone

Shield3

Louis Marquenet

Opsek

Pablo Sabbatella

SEAL | Opsek

Dickson Wu

SEAL

Private Key & Seed Phrase Management

The seed phrase (or mnemonic phrase) is the master key to a non-custodial wallet, granting complete control over all its derived private keys and assets. The management of this phrase is the single most important aspect of self-custody security.

⚠️ If you suspect for even a moment that your private key or seed phrase has been lost, viewed by another person, or exposed digitally (e.g., shown on-screen, copied to a clipboard on a connected device), you must consider it compromised. Immediately create a new, secure wallet and transfer all assets to it.

Secure Storage Practices

The goal is to protect the seed phrase from both physical threats (theft, fire, water damage) and digital threats (hacking, malware). The foundational principle is to keep your seed phrase offline at all times.

As soon as a new wallet is created, back it up using one of the following offline methods. Wallet providers do not have access to your seed phrase and cannot help you recover it.

• Physical Written Copies: Writing the phrase on paper or a notebook is a common starting point. To mitigate risks of loss or damage from fire or water, store multiple copies in secure, geographically separate locations (e.g., a personal safe, a trusted family member's home, a bank deposit box).

• Durable Metal Storage: For superior protection against physical damage, etch or stamp your seed phrase onto a metal plate (e.g., steel, titanium). Commercial products are available for this purpose. These should also be stored in secure, separate locations.

Enhanced security option

For extra security, split seed into 3 pieces:

• Piece 1: Words 1-16
• Piece 2: Words 9-24
• Piece 3: Words 1-8 and 17-24

Storage locations:

• Different secure locations (safe deposit box, home safe, trusted family)
• Each piece stored with clear labeling system

Tamper evident bags:

Storing sensitive devices or documents in a tamper evident bag offers high confidentiality and integrity. You can sign & date these bags, and also take a picture of its serial number.

Use case: You can put your Piece 1: Words 1-16 of your seed, inside a safe. Piece 2: Words 9-24 of your seed, somewhere safe (different location) in a tamper evident bag (could be at your parents place). Piece 3: Words 1-8 and 17-24 of your seed, somewhere safe (different location) in a tamper evident bag (could be somewhere else, at a family member or trusted friend). You can put your backup ledger while traveling inside this, in the safe of your hotel room to detect tampering. The main idea is to never have at the same place your 24 words, but still be able to recover your seed within 2 pieces of paper out of 3. You can find a useful link here to our EthCC swag that shows you how to easily split your seed in 3 as recommended.

Prohibited Practices

Under no circumstances should you ever store your seed phrase in any of the following ways:

• Taking a digital photograph of it.
• Uploading it to cloud storage (iCloud, Google Drive, Dropbox).
• Sending it via text message or any messaging app.
• Sending it in an email, even to yourself.
• Storing it in a plain text file on a computer or phone.
• Sharing it with anyone. Wallet providers will never ask for your seed phrase.
• Password managers or digital storage
• Traveling with seed phrases
• Storing all pieces in same location
• Using a device obtained from an untrusted source, such as a conference, hackathon, or third-party online marketplace, as it may be tampered with.

Organizational Seed Phrase Security

For organizations managing multisig wallets, seed phrase security requires additional properties beyond individual storage:

Security Properties

• Disaster Resistant: The seed phrase is either duplicated or split, with components/copies secured across multiple geographic locations. This way, if disaster strikes, keys can be recovered from other locations.
• Theft Resistant: An attacker gaining access to one piece of physical storage media for the seed phrase would not allow them to rebuild the wallet on its own
• Operator Loss Resistant: Reconstituting the seed phrase should be possible with the absence of one or more operators

Seed Phrase Encryption

⚠️ Warning: Encryption adds recovery risk. Only implement custom encryption schemes if you are sophisticated and have robust documentation practices. If you forget your encryption method or passphrase, your funds are permanently inaccessible—there is no recovery option. Many users and organizations face greater risk of locking themselves out with custom encryption than from an attacker discovering a securely stored backup. Evaluate whether strong physical security alone may be sufficient for your threat model.

The reason to encrypt seed phrases is that if they are discovered unencrypted, the wallet is permanently compromised. However, if you encrypt your seed phrase, you are much more likely to forget the encryption when trying to restore the wallet. If you have stored the seed securely, it is unlikely to be discovered in the first place.

Never store seed phrases in plain text or on an internet connected device. For additional protection, seed phrases can optionally be encrypted through some method. For example:

• Seed phrases can be mixed in a randomly generated, recorded order
• Have a 25th secret word
• Require a passphrase to be imported into a wallet

Regardless of the method, the related secret value should be stored in a password manager. (Do not store your seed phrase in a password manager.)

Advanced Backup Options

Split the key into multiple shards and securely distribute them:

• Use Shamir's Secret Sharing algorithm for N of M key shards
• Consider using this Shamir Secret Sharing implementation
• Seed phrases can be sharded using Shamir's Secret Sharing algorithm, with each shard recommended to be shared with a trusted guardian (3rd party custodian service, family members, password manager, personal physical media, etc.)

Use device-supported multi-share backups where available:

• Trezor Multi-Share Backup

Give shards to trusted family members, put in bank safe deposit boxes, and keep hidden around your house.

Multisig Social Recovery

Optional Self-Recovery:

• Seed phrase backups are not strictly necessary with a healthy quorum
• Multi-sig signing wallets should not be used for any other purpose and could be re-provisioned by existing quorum admins
• Maintain a healthy enough signing pool that loss of access to a few accounts at once could be recovered from
• Personal backup methods for admins are required to maintain access to on-chain assets in the event of loss of access to hardware wallets

Quorum Social Recovery: If access to wallet is lost, the quorum can vote to edit members to replace the inaccessible wallet.

Ongoing Security Hygiene

On a recurring basis (e.g., every 6 months), conduct a security review by asking:

• Do I know the physical location of all my seed phrase backups?
• Are my storage methods still secure and uncompromised?
• If my primary device were destroyed, do I have a clear plan to recover my assets?

While you can use the same keys for years, it is a best practice to periodically rotate them by moving assets to new wallets.

Establish a clear, secure protocol for a trusted next-of-kin to access your assets in case of incapacitation or death. This may involve sealed instructions stored with a lawyer or in a safe deposit box.

Emergency access plan

Trusted contacts

• Designate 2-3 trusted individuals who can access backup locations
• Clear instructions for emergency seed access
• Regular check-ins with trusted contacts

Recovery scenario example

"Call [trusted person] with code word [predetermined phrase], tell them to get the metal plate from safe location A, they give you words 1-16 over the phone. Then call [second person] with code word for location B to get words 9-24. Use both pieces to reconstruct seed immediately, then change all security settings."

Documentation

• Emergency contact information stored separately from seed
• Code words/phrases for identity verification
• Access instructions for trusted contacts
• Regular testing of emergency procedures
• Update procedures when contacts or locations change

Remember: Your seed phrase security is the foundation of multisig security. Take time to implement proper storage procedures appropriate for your risk level.