BIP39 passphrase generator

BIP39 (Bitcoin Improvement Proposal 39) defines how a random number is turned into a list of 12 to 24 common words, the mnemonic or seed phrase that backs up most cryptocurrency wallets. Words are far easier to write down and check than a long hexadecimal number. This tool generates mnemonics from entropy and converts between entropy and mnemonic so you can understand and test the process.

How to use it

1. Generate random entropy, or paste existing entropy in hex.
2. Read the corresponding mnemonic in the chosen word-list language.
3. Or paste a mnemonic to recover the entropy it represents.

How BIP39 works

Entropy of 128 to 256 bits is generated. A checksum equal to the first (entropy bits / 32) bits of its SHA-256 hash is appended. The combined bits are split into 11-bit groups, and each group (0 to 2047) selects a word from the 2048-word list. 128 bits of entropy plus a 4-bit checksum gives 132 bits, or 12 words; 256 bits plus 8 checksum bits gives 24 words.

Example

All-zero 128-bit entropy, 00000000000000000000000000000000, produces the well-known test phrase abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon about. The final word differs because it contains the checksum.

Safety warning

• Use generated phrases for learning and testing only. Create real wallet seeds on a hardware wallet or trusted offline device.
• Never paste a real seed phrase into any website. Anyone who has it controls the funds.
• An optional BIP39 passphrase adds a 25th word that changes every derived key.