BIP39 Checksum Checker

Disclaimer

This was purely for learning and educational purposes. While it should work, it is not intended to be used as a recovery tool, and I do not recommend relying on it.

There are far more reputable tools available such as Ian Coleman's BIP39 Tool and Bitcoiner's Seed Tool. Just remember to run them offline on an airgapped computer that is never connected to the internet.

This script analyzes BIP39 seed phrases, specifically focusing on 12-word or 24-word seed phrases (Most common).

Given the first 12 or 23 words, it will generate all the possible final (12th or 24th) words.

What is BIP-39?

BIP-39 stands for Bitcoin Improvement Proposal 39. It defines a standard for creating human-readable mnemonic phrases (typically 12 or 24 words) that can be used to generate deterministic wallets — most commonly used in Bitcoin and many other cryptocurrencies.

Instead of a hex string, for example:

07cf7730bca69cd65b59d459bcdd24ed386a4ee1740f20b98d70c489f1ad64db3c468c11615efe88b3bf3554025447149239d77e48ded1c15eededa77be77c46

BIP-39 means you will get a mnemonic phrase that reads like (for example) :

actual enroll require budget imitate random radar adult bright battle harbor fluid among sense blame afraid era silver please tuna bracket dry rent leave

They both represent the same thing but one is:

• Easy to read and write down or memorize
• Deterministic. The same phrase always generates the same wallet)
• Compatible across many wallets (e.g., Ledger, Trezor, MetaMask)
• Recoverable — lose your device, keep your phrase, you still have your Bitcoin

How BIP39 Seed Phrases Work

12-word Seed Phrase Construction

• First 11 words provide 121 bits of entropy (11 × 11 bits per word)
• 7 additional bits are added to make 128 bits of entropy
• A 4-bit checksum is calculated by taking the first 4 bits of the SHA256 hash of the 128-bit entropy
• The 12th word is determined by combining the 7 additional bits and the 4-bit checksum to form an 11-bit index

24-word Seed Phrase Construction:

• First 23 words provide 253 bits of entropy (23 × 11 bits per word)
• 3 additional bits are added to make 256 bits of entropy
• An 8-bit checksum is calculated by taking the first 8 bits of the SHA256 hash of the 256-bit entropy
• The 24th word is determined by combining the 3 additional bits and the 8-bit checksum to form an 11-bit index

Usage

python3 get-checksum-12-words.py "word1 word2 word3 ... word11"

python3 get-checksum-24-words.py "word1 word2 word3 ... word23"