What Is a Seed Phrase?

A seed phrase is a sequence of 12, 18, or 24 random words generated when you create a new crypto wallet. It encodes the master private key from which all your wallet's individual keys and addresses are derived.

An example (never use this โ€” it's for illustration only):

witch collapse practice feed shame open despair creek road again ice least

Never use example phrases. The phrase above is from public documentation and any funds sent to it will be stolen immediately.

The BIP-39 Standard

Seed phrases follow the BIP-39 (Bitcoin Improvement Proposal 39) standard, which defines a wordlist of 2,048 carefully chosen English words. The words are selected to be visually and phonetically distinct to minimize transcription errors.

  • 12 words = 128 bits of entropy (standard for most wallets, very secure)
  • 24 words = 256 bits of entropy (used by Ledger and Trezor hardware wallets)

The number of possible 12-word seed phrases is 2ยนยฒโธ โ€” a number with 39 digits. Brute-forcing one is computationally impossible.

From Seed to Keys

The seed phrase is processed through PBKDF2 (with HMAC-SHA512) to generate a 512-bit seed. This seed then feeds into the BIP-32 HD wallet derivation tree:

  • Seed โ†’ Master Private Key
  • Master Private Key โ†’ Account Private Keys (per derivation path)
  • Account Private Keys โ†’ Individual Address Keys

One seed phrase = full control over every address and every coin across every blockchain supported by that wallet.

How to Store Your Seed Phrase

Do:

  • Write it on paper with a permanent marker
  • Store it in a fireproof and waterproof location
  • Consider engraving it on stainless steel for fire/water resistance
  • Keep multiple copies in different secure physical locations
  • Consider a safety deposit box for large holdings

Don't:

  • Take a screenshot or photo
  • Store in cloud storage (iCloud, Google Drive, Dropbox)
  • Type it into any website, email, or chat
  • Store in a password manager (if that gets hacked, everything is gone)
  • Share it with anyone โ€” even "wallet support"

The golden rule: Anyone who has your seed phrase has your crypto. Treat it with the same seriousness as a large amount of physical cash.

The Optional 25th Word (Passphrase)

Advanced wallets support an additional BIP-39 passphrase โ€” sometimes called the "25th word." This is a custom word or phrase you choose that creates an entirely different wallet from the same seed. Benefits:

  • Even if your 12/24 words are compromised, funds are still safe
  • Can be used to create "decoy" wallets with small amounts
  • Must be memorized or stored separately from the seed