Seed phrase safety: what it is and how to protect it
A seed phrase (recovery phrase) is a list of 12, 20 or 24 words that can recreate every key in your wallet. Anyone who sees it can take your funds, so write it on paper or metal, keep it offline and private, and never type it into a website or give it to anyone, including support.
What is a seed phrase?
A seed phrase encodes a large random number in human-readable words. Your wallet derives every private key and address from it, for every network it supports. Most wallets use the BIP39 standard, which picks words from a fixed list of 2,048 English words. Restore the same phrase in a compatible wallet and the same addresses and balances appear.
Other names for the same thing: recovery phrase, mnemonic, secret recovery phrase (MetaMask), backup phrase, 24 words (Ledger).
12 vs 24 words (and 20)
| Format | Security | Used by default on (examples) |
|---|---|---|
| 12-word BIP39 | 128-bit | Most software wallets, e.g. MetaMask, Trust Wallet, Phantom |
| 24-word BIP39 | 256-bit | Ledger devices, Trezor Model One |
| 20-word SLIP-39 (single share) | 128-bit; extra words store metadata and checksum | Trezor Safe 3 (from June 2024), Safe 5, Safe 7 |
Trezor's own guide calls all of these "extremely secure": guessing a properly random 12-word phrase is not feasible (Trezor, checked Oct 2026). The real risks are a phrase that was not random (a bad generator) or a phrase someone else sees. The last word of a BIP39 phrase includes a checksum, so a random typo is usually caught on restore.
Weak randomness has caused real losses: the Milk Sad flaw in the bx seed tool (more than $900K, Aug 2023), Trust Wallet's WebAssembly entropy bug (about $170K, Apr 2023) and the Coldcard firmware 4.0.1 build error, exploited from 30 July 2026 (about $116M by TRM Labs' count). Never use a phrase generated by a website or given to you by someone else.
The BIP39 passphrase ("25th word")
Many wallets, including Ledger and Trezor, let you add an optional passphrase on top of the seed phrase. Each different passphrase opens a completely different wallet. It protects you if someone finds your written phrase, and Trezor says it defeats the physical extraction attack Kraken Security Labs showed on its older devices in January 2020 (The Block, Jan 2020).
- Upside: a found seed phrase alone is useless.
- Downside: forget the passphrase and the funds are gone. Nobody can reset it.
- Store the passphrase separately from the seed phrase, and test recovery with a small amount first.
How to store a seed phrase
| Method | Verdict |
|---|---|
| Paper, handwritten, kept private | Good starting point; protect from water and fire |
| Metal plate or stamped steel | Best for long-term holdings; survives fire and flood |
| Two copies in different secure places | Good against loss; each copy is another place it can be found |
| Photo, screenshot, cloud notes, email, chat | Avoid: malware and account takeovers target these |
| Password manager | Avoid for meaningful amounts; online vaults have been stolen and cracked |
| Split into halves | Avoid: it weakens security; use a passphrase, SLIP-39 shares or multisig instead |
For larger sums, consider removing the single point of failure altogether: Trezor's multi-share backup (SLIP-39), a multisig smart account such as Safe, or an inheritance plan that tells a trusted person where the backup is without giving them the words today.
Scams that target your seed phrase
- Fake support. Accounts on X, Telegram and Discord reply to complaints and send you to a "validation" form.
- Letters and emails. Physical letters on fake Ledger and Trezor letterhead demanded a "mandatory" check via QR code (The Block, Apr 2025; BleepingComputer, Feb 2026). In September 2026 attackers who breached Trezor's email provider Brevo sent phishing from Trezor's real support address; Trezor took the site down within about 20 minutes (BleepingComputer, Sep 2026).
- Fake apps. Fake Ledger Live apps on the Microsoft Store (about $768K, Oct 2023) and Mac App Store (about $9.5M, Apr 2026) asked users to "restore" with their phrase. See fake wallet apps.
- Tampered devices. Pre-filled recovery cards in the box, or devices bought from unofficial resellers. A genuine wallet always generates a new phrase for you.
- Photo-scanning malware. SparkCat used on-device text recognition to find photos of recovery phrases (The Hacker News, Feb 2025).
The rule: the only place your seed phrase should ever be typed is the wallet itself during a restore you started, ideally on a hardware wallet. Nobody legitimate will ever ask for it. If you think it has been seen, create a new wallet now and move everything.
Frequently asked questions
Is a 12-word seed phrase safe enough?
Yes, if it was generated randomly by a reputable wallet. A 12-word BIP39 phrase has 128 bits of security, which Trezor describes as extremely secure. Theft and loss are the real risks, not guessing.
What is the difference between a seed phrase and a private key?
A private key controls one address. A seed phrase generates many private keys across many networks, so it backs up the whole wallet.
Can I recover a wallet without the seed phrase?
Only if the wallet uses another recovery method, such as MPC shares, backup cards or a smart account. For a standard seed phrase wallet, no: nobody can reset it.
Should I use a BIP39 passphrase?
It adds strong protection if someone finds your written phrase, but if you forget it your funds are lost. Use it only if you can back it up reliably and separately.
What should I do if I typed my seed phrase into a website?
Assume it is compromised. Create a brand-new wallet with a new phrase on a clean device and move all funds immediately, starting with the most valuable.
Can I store my seed phrase in a bank safe deposit box?
Many people do. It protects against fire and burglary at home, but consider access delays and who else could open it, and keep a second copy elsewhere.