Overview
A mnemonic phrase (also known as a seed phrase or recovery phrase) is a sequence of 12 or 24 English words that encodes the master secret from which all keys in a hierarchical deterministic (HD) wallet are derived. Defined by the BIP39 standard, the mnemonic provides a human-friendly way to back up and restore a wallet's entire key tree.
How It Works
1. Generate random entropy (128 or 256 bits)
2. Compute checksum (first 4 or 8 bits of SHA-256)
3. Append checksum to entropy
4. Split into 11-bit segments
5. Map each segment to a word from the 2,048-word BIP39 list
128 bits → 12 words
256 bits → 24 words
Example (12 words):
abandon ability able about above absent
absorb abstract absurd abuse access accident
From Mnemonic to Keys
The mnemonic words are converted into a 512-bit seed using PBKDF2 with an optional passphrase. This seed is then used as the root of a BIP32 HD wallet tree, from which all private keys, public keys, and addresses are deterministically generated.
Mnemonic Words + Optional Passphrase
│
PBKDF2 (2048 rounds)
│
512-bit Seed
│
BIP32 Master Key
/ \
Child Child
/ \ / \
... ... ... ... ← All addresses
Security Considerations
Anyone who obtains the mnemonic phrase gains complete control over all funds in the wallet. The phrase must be stored securely — ideally on a physical medium (metal plate, paper) in a safe location, never digitally on internet-connected devices. The optional BIP39 passphrase adds an extra layer of protection, creating an entirely different wallet for each passphrase used.
Common Misconceptions
The 12 or 24 words are not random — they come from a specific 2,048-word list, and the last word includes a checksum. Entering a random selection of words from the list will almost certainly fail validation. Also, the same mnemonic with different derivation paths (BIP44, BIP84, BIP86) will produce different addresses, which is why wallet software must know the correct path to restore funds.