Security
BIP39 Passphrase Generator
The BIP39 Mnemonic Generator creates cryptographically secure seed phrases (mnemonic codes) for cryptocurrency wallets and derives the corresponding seed bytes and HD wallet root keys. It supports 12, 15, 18, 21, and 24-word phrases, the full 2048-word BIP39 wordlist in multiple languages, and optional BIP39 passphrase (25th word). All entropy generation and key derivation runs in the browser – no sensitive data is ever sent to a server.
What is BIP39?
BIP39 (Bitcoin Improvement Proposal 39) defines a standard for generating a deterministic wallet from a human-readable mnemonic phrase (seed phrase). The proposal, authored by Marek Palatinus, Pavol Rusnak, Aaron Voisine, and Sean Bowe in 2013, allows users to back up and restore their entire wallet using 12–24 simple English (or localized) words instead of a raw cryptographic key. The mnemonic encodes 128–256 bits of cryptographically random entropy plus a checksum. From the mnemonic, a 512-bit seed is derived using PBKDF2 with HMAC-SHA512 (2048 iterations), which is then used to generate all private keys in an HD (Hierarchical Deterministic) wallet tree as defined by BIP32.
How does the generator work?
The tool generates cryptographically secure random entropy bytes using the browser's crypto.getRandomValues() API (128 bits for 12 words, up to 256 bits for 24 words). A checksum (first ENT/32 bits of SHA-256 of the entropy) is appended. The combined bit string is split into 11-bit groups, each mapped to a word in the 2048-word BIP39 wordlist. The mnemonic is then converted to a seed using PBKDF2-HMAC-SHA512 with 'mnemonic' + optional passphrase as the salt and 2048 iterations. The seed is used to derive the BIP32 root key (xprv/xpub). Validation mode checks whether an entered mnemonic has a valid checksum.
Typical Use Cases
- Generating a new BIP39 seed phrase for a software or hardware cryptocurrency wallet
- Validating that a manually entered mnemonic has a correct checksum before importing
- Learning how BIP39 entropy, checksum, and word mapping work
- Deriving the HD wallet root key from a mnemonic for testing purposes (never with real funds)
Step-by-step Guide
- Step 1: Select the number of mnemonic words (12, 15, 18, 21, or 24).
- Step 2: Optionally select a language for the wordlist (English, Japanese, Chinese, etc.).
- Step 3: Click 'Generate' to create a new random mnemonic.
- Step 4: Optionally enter a BIP39 passphrase and copy the seed and root key.
Example
Input
12 words, English wordlist, no passphrase
Output
abandon ability able about above absent absorb abstract absurd abuse access accident
Tips & Notes
- Write down your seed phrase on paper and store it in a physically secure location – anyone with access to the seed phrase can access all funds in the wallet.
- Never enter a real seed phrase into an online tool or any software you do not fully trust. Use this tool only for learning, testing, or generating new phrases (not for existing wallets).
- The BIP39 passphrase (25th word) adds an extra layer of security; even if someone obtains your 12–24 word phrase, they cannot access funds without the passphrase.
Frequently Asked Questions
How secure is a 12-word vs a 24-word mnemonic?
A 12-word mnemonic encodes 128 bits of entropy (plus 4-bit checksum), which is considered computationally infeasible to brute-force. A 24-word mnemonic encodes 256 bits. The difference in security is theoretical for most purposes; both are practically unbreakable if generated from true random entropy.
What is the BIP39 passphrase?
The BIP39 passphrase (sometimes called the 25th word) is an additional string appended to the mnemonic during seed derivation. It is not stored in the mnemonic and must be remembered separately. A different passphrase produces a completely different wallet, enabling plausible deniability.
Can I use a BIP39 mnemonic for any cryptocurrency?
BIP39 mnemonics generate a universal seed. Which cryptocurrencies are accessible depends on the derivation paths used by the wallet software (BIP44/49/84/86 define standard coin-type paths for Bitcoin, Ethereum, etc.).
BIP39 Passphrase Generator
Generate BIP39 mnemonics from cryptographically secure randomness and derive seeds. Supports English and German. Validate existing mnemonics.
Open Tool