Seed phrase

The phrase is not a password and not an account name: it is the wallet itself, compressed into words a human can copy by hand. Twelve words carry 128 bits of randomness, which is why the list is short enough to write and still impossible to guess. Anyone who reads it can spend everything the wallet will ever hold, including coins you have not bought yet.

How it works

Your wallet generates a random number first and finds words for it second. A device produces 128 or 256 bits of entropy, appends a short checksum, and slices the result into groups of 11 bits. Each group indexes a fixed list of 2,048 words, giving 12 words for 128 bits and 24 for 256. The words are a transcription, chosen because people mis-copy characters and rarely mis-copy common English.

Order is part of the secret. The same twelve words in a different sequence describe a different number and therefore a different wallet, so a backup that lists them unnumbered is a puzzle waiting for your heirs. Spelling matters less than people fear, because every word in the English list is uniquely identified by its first four letters, and most wallets accept those four alone.

The checksum is the reason a mistyped phrase is usually rejected rather than silently accepted. Four of the 132 bits in a 12-word phrase are derived from the rest, so a phrase with a wrong or transposed word fails validation roughly fifteen times out of sixteen. That is a typo catcher, not a security feature: it will not tell you that word nine should have been "orbit" instead of "orbits".

What the phrase is not is an online credential. There is no server anywhere that stores it, no rate limiting, no lockout after three attempts, and no reset. Restoring is a calculation that any wallet on any continent can perform offline, which is exactly why a photographed phrase is a spent wallet.

Why this matters when you buy bitcoin

The moment you withdraw from an exchange, your seed phrase becomes the whole of your security. Every platform reviewed on this site can help you recover an account after a lost password. None of them can help after a lost phrase, and none of them will ever ask for one.

That asymmetry is why recovery phrases are the single most attacked object in bitcoin. Fake support agents in comment replies, "wallet validation" pages that appear when you search for a wallet's name, browser extensions that mimic a restore screen, and airdrop sites that request a phrase to "check eligibility" all exist for this one string. The FBI's Internet Crime Complaint Center logged more than 9.3 billion dollars of cryptocurrency fraud losses reported in 2024 alone, and a large share begins with a phrase typed into the wrong box.

Offline attacks are just as real. Ledger's e-commerce database was breached in June 2020, exposing 1,075,382 email addresses and 272,853 detailed order records including names, phone numbers, and delivery addresses. Customers on that list received convincing letters, calls, and even counterfeit devices for years afterward, all engineered to make them enter their words. Owning a hardware wallet does not make you immune to a story that arrives on paper.

The rule that survives every variation of the scam: nothing legitimate ever needs your phrase. Not a firmware update, not a support ticket, not an exchange, not a tax tool, not a "wallet migration". Type it only into a wallet you deliberately installed, on a device you control, at a moment you chose.

Writing down words so they survive

Treat a seed phrase backup as two separate problems: making it durable, and keeping it away from people.

For durability, the first copy is pen on card, written the moment the wallet shows it. Number each word. Note which wallet made it and which derivation path or script type it uses, because that saves an afternoon of confusion during a restore. Then transfer the same words to stamped or punched stainless steel. Prefer solid steel you mark yourself over plated tiles, printed strips, or glued assemblies, since the failure you are buying against is a house fire and a flooded basement rather than a careless housemate.

For secrecy, keep two copies in different buildings, and pick the second location for boring reliability rather than cleverness. Buried tubes and hollowed books lose more coins than burglars do. Never store the words in a password manager, a photo library, a note-taking app, or an email draft, and never read them aloud to a phone.

Then test it. Restore the phrase into a second wallet or a wiped device before the balance grows, confirm the first receiving address matches, and wipe the test wallet afterward. Repeat the drill every year or two, because handwriting fades and memory of where the second copy went fades faster.

Seed phrase vs private key

A seed phrase is the root that produces keys; a private key controls one specific set of coins. The relationship runs one way: from the phrase you can derive every key, but from a single key you can never work backwards to the phrase or reach any sibling. That is why exporting one private key for a specific purpose is survivable and exporting the phrase is not, and why wallets keep individual keys hidden while showing the phrase exactly once.

Seed phrase vs passphrase

A seed phrase is generated by the device; a passphrase is an optional extra secret you invent and add to it. They combine into one wallet, so both are needed to recover, and they should not be stored in the same place. Confusing the two is a common and expensive error, most often when someone writes their passphrase as a thirteenth or twenty-fifth line on the same card, which removes the protection entirely while doubling the number of things that can be mistyped.