What is BIP39?
- Author
- CRYPTO PORT Editorial
- Published
- Updated
- Reading time
- 5 min
In short
BIP39 is the specification for turning a random value into a word list used as a wallet backup. Because it is a shared standard, a phrase created in one wallet can be restored in another vendor's software. The list holds 2,048 words, and a checksum is folded into the final one.
Key points
- A 2,048-word list, 11 bits per word
- A checksum in the last word catches transcription errors
- An optional passphrase is part of the standard
- It is why phrases restore across different vendors
Definition
Bitcoin Improvement Proposal 39, which defines how to turn entropy into a mnemonic phrase and how to derive a wallet seed from that phrase.
The procedure is fixed. Take 128–256 bits of entropy, append the first few bits of its SHA-256 hash as a checksum, then split the result into 11-bit chunks and map each to a word. 128 bits plus a 4-bit checksum is 132 bits, which divides into 12 words; 256 bits gives 24.
The phrase is then stretched through 2,048 rounds of PBKDF2 into a 64-byte seed. The standard allows an arbitrary passphrase to be mixed in at this step, so the same words with a different passphrase produce a completely separate wallet. Entering nothing means the empty string.
The real value of a public word list is that your funds survive the vendor. Any wallet advertising BIP39 support can restore a phrase from any other, so a company folding does not strand you. Derivation-path conventions still vary by product, so check that setting when you migrate.
Watch out for
- · Never use an online phrase generator; the value it shows you may have been logged
- · Forget that you set a passphrase and the correct words alone will not restore the wallet
- · A valid checksum does not confirm the phrase matches the one you wrote down