BIP39 Mnemonic Converter

BIP39 (Bitcoin Improvement Proposal 39) standardises the generation of deterministic wallets from a human-readable mnemonic phrase. A random entropy value (128–256 bits) is hashed with SHA-256, a checksum is appended, and the result is split into 11-bit groups that index into a 2048-word wordlist. The mnemonic is then converted to a 512-bit seed via PBKDF2-HMAC-SHA512 with 2048 iterations, which seeds a BIP32 hierarchical deterministic wallet.

The BIP39 passphrase is an optional additional input to the PBKDF2 seed derivation function. It is sometimes called the 25th word but is not from the BIP39 wordlist — it can be any string. Using a passphrase creates a completely different wallet from the same mnemonic, providing plausible deniability: you can have a decoy wallet with small funds at the mnemonic alone and a main wallet at mnemonic + passphrase.

12 words = 128 bits of entropy, 15 words = 160 bits, 18 words = 192 bits, 21 words = 224 bits, 24 words = 256 bits. With 128 bits, the search space is 2¹²⁸ possible mnemonics — computationally infeasible to brute-force with any foreseeable technology. The extra bits in 24-word phrases provide a larger margin against future cryptanalytic advances but are not practically necessary for current security.

A real wallet mnemonic is the master key to all funds. Any tool, website, browser extension, or clipboard that sees your mnemonic could exfiltrate it. For practice and learning, test with example or randomly generated phrases. For real wallets, generate and store the mnemonic on air-gapped hardware (hardware wallets like Ledger or Trezor) and never type it into any internet-connected device.