Twelve words. It only takes one to rebuild an entire crypto wallet from scratch: all addresses, all private keys, all coins within a wallet. Also, it’s enough for a stranger to drain that same wallet in minutes if such words end up in a place they shouldn’t. It’s a short list of regular words, and it’s, with few equals, the most important piece of information in cryptocurrency.
A seed phrase is a 12 to 24-word sequence of random, normal words, which can be automatically generated by a crypto wallet, that can recreate all the private keys the crypto wallet controls. It will be referred to as a recovery phrase, a backup phrase, or a mnemonic phrase all terms for the same idea. Take out the device that the wallet is on, and the seed phrase restores everything. On purpose or by accident, pass those words on, and the wallet’s now out of your control, forever, without any means of reversal.
Here’s the short answer. The remainder of this guide provides details on where these words actually come from, why the format is 12 or 24 instead of some other number, why a few syllables can actually lead to real cryptographic security, and, even more importantly, how not to become one of those who lose crypto to a seed phrase error each year.
Where a Seed Phrase Actually Comes From
The wallet software does not ask you to come up with a name when you open the wallet for the first time and click “create new wallet”. It generates a large random number (between 128 and 256 bits) somewhere, using your device’s random number generator. As such, it is difficult to read and may be easily mistyped: a long and meaningless string of binary digits.
The wallet feeds that number into a standard, called BIP-39 (Bitcoin Improvement Proposal 39), which was released in 2013, which makes it usable. BIP-39 divides the number into small parts, and assigns each part to a word from a fixed list of 2,048 words, no fan mail here, just garden, orbit, harvest, etc. The checksum from the original number is folded in too, so that a wallet can instantly detect if a word was mistyped or out of order on the recovery: The math doesn’t work.
The answer comes across like a bizarre shopping list, something like orbit, garden, velvet, comfort, sudden, north, panther, echo, harvest, ladder, mimic, glass, but is actually a random number that a human being may be able to copy down, read aloud to, or retype into a new phone without making mistakes. As BIP-39 is not a proprietary implementation, a seed phrase created with MetaMask will be restored correctly with Trust Wallet, Ledger, Exodus or any one of the dozens of wallets that adhere to the BIP-39 standard.
Why 12 Words, 24 Words, and Not Some Other Number
The word count is not a style it’s a direct reflection of the security behind it. A 12-word phrase is pretty much 128 bits of entropy, a 24-word phrase is 256 bits. So a 24-word seed is not just twice the protection of a 12-word seed. It’s the size of a search space that’s so vast that it becomes impossible to consider it in practical terms.
To put that into perspective, the 128 bits are well beyond the capability of any current or future computer to brute-force. Most software wallets default to 12 words, which is considered to be a safe range for cryptographers for the foreseeable future, and they consider 12 words to be enough. Companies such as Ledger and Trezor tend to default to 24 words, partly for precaution and partly to allow for the ability for any future computing power to become greater, but without changing the meaning of the 24 words themselves day to day. Now and then, you will find phrases that are 15 words, 18 words, or 21 words as well, since there are several lengths of steps, BIP-39 supports 12 and 24, which is what you will find almost everywhere in practice.
One Phrase, Every Address You’ll Ever Use
A seed phrase is not just for one wallet address. It’s the basis for all wallet addresses the wallet will ever create. This is because almost all modern wallets are hierarchical deterministic (HD) wallets, a standard that is specified in BIP-32, and another standard, BIP-44, that specifies how each cryptocurrency has its own branch of the hierarchical structure. An HD wallet uses one seed to create a whole tree of private keys – a branch for Bitcoin, a branch for Ethereum, a branch for each new account within those networks.
The process is deterministic, that is, the same seed phrase, when run through the same derivation path, always yields the same private keys and addresses, regardless of the device used. That’s what makes recovery possible at all. When you go into the wallet and type your words into a new phone, it is going to use math to recalculate that account, which it has no access to, it will happen instantly and it won’t pull anything off of a server from any company. It’s also how a single seed phrase is able to control every address on every blockchain you’ve ever been to with that wallet, even those you forgot about.
The difference between a Seed Phrase, Private Key, and Public Key
In fact, these three terms are all confused, and wallet interfaces don’t always make it clear. Here’s the actual hierarchy: your seed phrase is the master backup. From it, your wallet mathematically generates a private key for each address you use, and a private key is the one that you are using to sign a transaction and is what you use to prove that you have the right to move the funds out of a particular address. Each private key is paired with a public key, which is the public component of the key pair that your address is constructed from, and which can be seen by everyone without risk, like a public key in any other system constructed using asymmetric cryptography.
Imagine it is three layers of security to a secret. The seed phrase is at the top and is capable of recreating all your private keys in that wallet. The private key is associated with just one address. If you lose one private key in a wallet where the seed is still stored, it’s a minor inconvenience that you can just regenerate the private key you lost. If it is lost or shared, it cannot be recovered and cannot be contained. It hands over the master key to everything that wallet has ever touched.
What if You Lose Your Seed Phrase?
There’s something that’s baffling most people the first time they hear it: Your cryptocurrency wasn’t really inside your wallet app! It is permanently stored on the blockchain and linked to a public address. So what is in your wallet and what can be built with your seed phrase is nothing more than the key that unlocks the door to entry and unlocks the ability to move it.
That distinction matters the moment something goes wrong. If you send a phone to the lake, you don’t lose your crypto, it will still be at the same address without you touching it. The seed phrase is a string of words that you enter into any wallet that supports it, and then you’re ready to rock in a matter of minutes. If it doesn’t exist, and if it originally didn’t exist, that balance will be visible to anyone who observes the blockchain and is permanently, forever inaccessible. No password reset! Luckily, there is no support line available because in a self-custody wallet, there was never a company that held onto your keys that’s the price you pay for full control. It’s also why the number of Bitcoin that are forever lost and unrecovered, for the most part from this exact situation, often exceed the millions.
Could Someone Just Guess Your Words?
Realistically, no. A 12-word BIP-39 phrase comes from a dictionary that contains a search space of approximately 2^128 possible combinations, which is sufficient to ensure that the probability of guessing a funded phrase is below one chance in the universe, even if every computer in the world ran for the age of the universe. The math isn’t the weak point.
People lose their crypto when they type it into a fake wallet-recovery website, when they paste it into a browser extension that pretends to be customer support, when they keep a screenshot in the camera roll that syncs to cloud storage automatically, or when someone they’ve met in a Discord or Telegram chat tells them they can help solve a wallet issue. None of those are math problems, none of them are human decisions, which is why there is an emphasis on habits, not cryptography, in seed phrase security advice.
The Blunders That Can Make People Lose Their Crypto
A legitimate wallet provider, exchange, or hardware wallet company will never request your seed phrase via a support ticket, over the phone, or in a pinned post within an official wallet company Discord server. Of course, that one rule will eliminate most seed phrase scams: If you get a message that your wallet needs to be verified, a pop-up that offers to sync your funds to another device, or an extension that says it can help you get your lost crypto back if you enter your words first, it’s a scam.
A similar scam is the seed phrase generator that some users will resort to rather than use the wallet app directly. There are lots of such tools that are just as they say, but a shady one could give you terms that the operator has actually typed out on their own, and you cannot tell simply by looking at it. Don’t deposit funds into an address provided by a wallet you don’t already trust if you didn’t create the phrase with that wallet.
Digital storage causes just as much damage. It’s possible for a photo with a seed phrase to be in a cloud backup, or in a recently deleted folder in the app, for several weeks even if you think you’ve removed it. A note you put in a default notes app on a mobile phone or a plain text field on a password manager is just a data breach away from being catalogued by anyone who has access to that database. Security research knows a name for malware designed to look for 12 or 24 words, in a row, that are composed of English letters. All these errors are not uncommon. They’re just handy that’s how they got so many people using them.
How to Store a Seed Phrase the Right Way
The words of advice that security professionals agree on are nearly the same each time, and that’s typically a positive sign: write it down, on paper or metal, and out of anything with a screen. Paper is required, has no monetary value, but is burnable, floodable, and fades over time. Several hardware wallet makers offer backup plates made specifically for this reason and cost only a little, and they’re worth it to anyone with a significant quantity of crypto.
Some habits go a long way to doing the work:
- Keep the written phrase in a drawer where no one visiting your home could access it, a home safe, or a safe deposit box.
- Store multiple copies in truly separate physical places so that if one copy is lost in a fire, flood, or theft, there are other copies remaining.
- Do not enter it into a computer, phone, or website, unless you are intentionally restoring a wallet you have decided to restore.
- No matter how convenient it may seem, don’t take photos of it, capture it on screen, or store it in a notes app, etc or in a password app or in the cloud.
- If the size of the holding is large, it’s possible to use Shamir’s Secret Sharing or combine it with a hardware wallet that stores the resulting private keys offline.
The final one deserves to be pondered. You can’t do without a seed phrase on a hardware wallet, as it is still created when the hardware wallet is set up, and the seed phrase must also be stored offline and carefully, as detailed above. You wouldn’t let your neighbor look after your child while you were away, so you shouldn’t let a computer virus sitting on your laptop do it, either: Your private keys are never sent away, and every single transaction has to be confirmed on your display, so the malware won’t get anything from you as long as you’re working on your computer.
Setting Up a Wallet Without Setting Yourself Up for a Loss
A little discipline at setup saves a lot of regret later. Always access the company’s official app and browser extension through the company’s website and/or an official app store listing and never by an ad link or direct message or a non-verified search result. When creating a wallet, take your time to remember to write down the words as soon as they are displayed, and only import a wallet if you are purposefully restoring a previously generated phrase. Most wallets require you to type in the phrase again immediately after you display it for them. They are a real check, not a chore, because there is nothing out there yet to lose.
Send a small amount of test transaction first, and check if you can access it only with the words you recorded, preferably on two different devices than the one you recorded with. It takes just some minutes and a few network costs, and it’s the only real method to be sure that your backup is functioning before it is the one factor between you and your money.
Passphrases, and Where the Seed Phrase Is Headed
Some wallets have an optional additional feature known as a passphrase, or 25th word. It is a custom word or phrase, which is applied to your base seed phrase, and generates a completely different, hidden wallet. If someone finds your word that you have written down without the passphrase, then he or she does not get your money, but an empty decoy. Powerful, but unforgiving: If you forget the passphrase, there is no way to recover the wallet that is protected, even if you have the base seed phrase right before your eyes.
The format itself is starting to change, too. A new generation of wallets is trying to eliminate the seed phrase completely from the wallet, distribute the key information among multiple parties via multi-party computation, or recover keys socially with the help of trusted contacts. While these are effective solutions to a genuine problem, and a seed phrase doesn’t require the trust of the company or protocol that will be responsible for its recovery, it is a different kind of trust. For now and for the vast majority of wallets currently being used, it’s the 12 to 24-word phrase, and knowledge of the phrase is, for now, the best thing you can do for your own security.
The One Thing Worth Remembering
Remove the cryptography, derivation paths, and the entropy maths, and a seed phrase is reduced to nothing more than one rule: whoever has the words has the funds, it’s as simple as that, and there’s no reversing it. All that is practically just a restatement of the one fact: Where to write it, how many copies to keep, which wallet to trust, all that. Use those words as seriously as a vault combination, instead of a website password, and the rest of managing your own crypto gets a lot less daunting.
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