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What is a seed phrase?
A seed phrase is a list of ordinary words, usually 12 to 24, that encodes the master secret of a wallet. Every private key in the wallet can be rebuilt from it, so it works as the backup for the whole wallet, on any compatible app or device.
What it means for you
Whoever has the words controls every account derived from them; the wallet's PIN or password does not stop them. Write the words in order, check the spelling against the 2,048-word list, and keep them offline. A missing or misspelled word can lock you out.
A common mistake: “Any 12 English words can work as a seed phrase.”
In fact: The words must come from the fixed 2,048-word list, in order, and the last word carries a checksum. Most made-up lists are rejected, and a wrong order produces a different wallet or none.
How it works
A wallet starts with 128 to 256 bits of random entropy, appends a checksum of one bit per 32 bits of entropy, and splits the result into 11-bit groups, each picking one of 2,048 words: 12 words for 128 bits, 24 for 256. The words are then run through PBKDF2, 2,048 rounds of HMAC-SHA512 salted with 'mnemonic' plus any passphrase, to make a 512-bit seed, from which BIP-32 derives every key. The first four letters identify each word, and because the last word carries the checksum, most random word lists fail validation.
An example
Say one word of a 12-word phrase is missing and you do not know which position. That is 12 positions times 2,048 words, or 24,576 candidates. A 12-word phrase carries a 4-bit checksum, so about 1 in 16 candidates passes, leaving roughly 1,500 to test against the wallet's known addresses.
Sources: BIP-39: Mnemonic code for generating deterministic keys, ethereum.org: Ethereum wallets, BIP-32: Hierarchical deterministic wallets · checked 4 October 2026
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