What is a seed phrase? How it works and how to keep it safe
What is a seed phrase? It is a list of words, usually 12 or 24, that a self-custody crypto wallet generates when you set it up. Those words let you restore the wallet and the funds it controls in an app that supports the same standard. Many wallets use the BIP-39 standard, assigned on 10 September 2013.
Whoever holds the words controls the funds, and if you lose them you may lose access for good. This page explains how a seed phrase works, how it differs from a private key, how to store it and who will try to get it from you. For the wider picture, read our guide to crypto wallets and security.
What is a seed phrase in crypto?
The US Securities and Exchange Commission describes it in its investor bulletin on crypto custody, published on 12 December 2025, as a random sequence of words that allows you to restore your crypto wallet if you lose it or your private key.
Other names for the same thing are recovery phrase, seed recovery phrase, backup seed phrase and mnemonic phrase. Each means the seed phrase crypto wallets show you at setup.
Seed phrases are used by self-custody wallets, both software and hardware. See how hardware wallets handle your recovery words.
An exchange account works differently. With third-party custody, the custodian controls the private keys, so you usually never see a seed phrase. With self-custody, you are solely responsible for your keys and seed phrase.
How a seed phrase works
The BIP-39 specification defines the mechanism. New to the topic? Our crypto basics for beginners cover the background.
Where the words come from
Your wallet generates random data, between 128 and 256 bits long, and adds a short checksum calculated from it. The result is cut into groups of 11 bits, and each group picks one word from a fixed list of 2,048 words. The amount of random data decides how many words you get:
| Random data (bits) | Words in the seed phrase |
|---|---|
| 128 | 12 |
| 160 | 15 |
| 192 | 18 |
| 224 | 21 |
| 256 | 24 |
The English list is designed so that the first four letters of each word identify it unambiguously. Similar pairs such as build and built are avoided.
From words to keys
The wallet turns the words, plus an optional passphrase, into a 512-bit seed using a function called PBKDF2 with 2,048 iterations. That seed then generates every key and address in your wallet through the hierarchical deterministic method described in BIP-32 or a similar method. BIP-32 was assigned on 11 February 2012.
This is why one phrase can restore the accounts in your wallet at once, as long as you restore it in a wallet that supports the same standard and enter the passphrase, if you set one. You back up one starting point, not a list of separate keys.
The checksum catches some typos, not all
The BIP-39 specification requires wallets to check the checksum and warn you when it is invalid. That is not a full safety net. The checksum is short, only 4 bits for a 12-word phrase and 8 bits for a 24-word phrase, so some wrong phrases still pass, and it cannot tell you which word is wrong. Copy the words exactly, in order.
Seed phrase vs private key
A private key authorizes transactions for the funds at the addresses it controls. The SEC bulletin states that if you lose your private key, you permanently lose access to the crypto assets in your wallet, which is why the seed phrase backup matters. A seed phrase is the backup that can regenerate all the private keys in the wallet.
| Private key | Seed phrase | |
|---|---|---|
| What it is | A secret that authorizes transactions | A list of 12 to 24 words that encodes the wallet's master secret |
| What it controls | The funds at its addresses | Every key and address the wallet derives |
| If it leaks | Someone can move those funds | Someone can restore the whole wallet and move everything |
In the private key vs seed phrase comparison, treat the seed phrase as the more sensitive item, because exposing it exposes every key it can create.
The optional passphrase (25th word)
BIP-39 lets you add a passphrase to the seed phrase. Every passphrase produces a valid seed and therefore a valid but different wallet. Only the correct passphrase opens your wallet. A wrong passphrase does not show an error; it opens a different, empty wallet.
If you forget the passphrase, the seed phrase alone will not recover your funds, so it needs its own storage plan. It reduces one specific risk, someone finding your written words, but it is not "unhackable" and does not make a wallet safe by itself.
How to store a seed phrase safely
The SEC's rule for seed phrase storage is short: store it in a secure place and do not share it with anyone. For crypto seed phrase storage, that means three habits:
- Write the words on paper by hand when the wallet first shows them, and keep the copy offline.
- Never photograph it, screenshot it, email it or paste it into cloud notes.
- Do not keep it in a password manager that syncs online.
Paper vs metal backups
Paper is cheap and easy, but it can burn, tear and fade. Metal seed phrase storage, such as an engraved plate or capsule, is an option. Judge any backup on neutral criteria:
- Fire and water resistance: does the material survive the events you worry about?
- Cost: paper costs almost nothing; metal costs more but does not burn, tear or fade like paper.
- Readability: can you read every word years later?
- Location: it must fit somewhere secure and away from your hardware wallet (see below).
If you searched for the best seed phrase storage, these criteria are the honest answer. The SEC notes that cold wallets are generally more secure from cyber threats but can be lost, damaged or stolen. A paper or metal backup carries the same physical risks. Read what a cold wallet is for more.
Where to keep it and who should know
Keep the backup in a separate place from your hardware wallet, so one theft does not take both. Consider too how a relative could find the words if something happened to you, without exposing them meanwhile.
Mistakes to avoid
- Writing the words in the wrong order or skipping one.
- Typing the phrase into any website, form or chat that asks for it.
- Splitting the words into home-made halves, because half a phrase gives a thief part of the secret and makes the rest easier to guess.
Who asks for your seed phrase (and why the answer is always no)
No legitimate person or company needs your seed phrase. You only ever type it into your own wallet app, during a restore you started yourself. The SEC says to never share your private keys or seed phrases. The CFTC page Beware Imposters states that the agency would never ask for your private keys or seed phrases.
Scammers still ask, and they use a few familiar approaches:
- Fake wallet support. A chat or direct message claims to be support and asks you to "verify" your wallet with your words.
- Recovery services. Someone offers to get lost crypto back for a fee. The CFTC publishes a warning titled "Don't be Re-Victimized by Recovery Frauds". Paid recovery offers are a known fraud pattern.
- Fake regulators. Someone poses as an agency and asks for your wallet details.
The Bitcoin Billionaire trading-robot scheme, which ran on this domain from 2020 until March 2026, relied on fake celebrity endorsements. Scams change, but the rule does not. Read about common crypto scams and how they work.
If you typed your phrase anywhere suspicious, treat the wallet as compromised. Create a new wallet with a new seed phrase on a device you trust, move the remaining funds to it straight away after checking the receiving address carefully, then report it. Never give the old phrase to a recovery service. In the United States, report crypto fraud to the FBI's Internet Crime Complaint Center (IC3) at ic3.gov. In England, Wales and Northern Ireland, report to Report Fraud, which replaced Action Fraud on 4 December 2025, at reportfraud.police.uk or on 0300 123 2040.
Frequently asked questions
What's a seed phrase used for?
It restores your wallet. The words regenerate the seed, and the seed regenerates your private keys and addresses through BIP-32 or a similar method, in a wallet that supports the same standard. Restore it in a seed phrase wallet that supports the same standard, and enter the passphrase if you set one.
Can I recover a wallet without a seed phrase?
Not with a self-custody wallet if you have lost both the phrase and the keys. Nobody can reset the keys for you. An exchange account is different, because the custodian controls the keys.
Is a 12-word or 24-word seed phrase safer?
Both lengths are standard. A 12-word phrase encodes 128 bits of random data and a 24-word phrase encodes 256 bits. Whichever you have, how you store and protect the words matters most.
Should I store my seed phrase in a photo or password manager?
No. Keep it offline and written by hand. A photo, screenshot or synced password manager entry puts the secret on devices and services that can be breached.
Will a wallet company or exchange ever ask for my seed phrase?
No. The CFTC says it would never ask for your private keys or seed phrases, and no genuine provider needs them. Treat anyone who asks as a scammer.