Your Bitcoin wallet is protected by 24 seed words that provide 256 bits of entropy - a measure of security complexity. However, these are at risk if they’re exposed. To add an extra layer of security, we use the BIP39 passphrase, often called the ‘25th-word.’ It acts as a 2nd-factor authentication (2FA) for your Bitcoin wallet.

 

 

The security of your passphrase depends on its entropy. We calculate entropy with this formula: bits of entropy = log2(no_of_combinations). The combinations depend on the type and number of words or characters you use for your passphrase.

 

Three methods are typically used to create passphrases:

 

1. BIP39-words: These are 2,048 pre-determined words. The entropy increases with each added word, starting from 11 bits with one word (2,048 combinations) to 132 bits with twelve words (5 duodecillion combinations).

 

2. English language words: Here you can pick from ~100,000 words. Entropy begins at 16 bits for one word (100,000 combinations) to 199 bits for twelve words (1 novemdecillion combinations).

 

3. ASCII characters: These include 95 characters like letters, numbers, and special characters. Entropy ranges from 6 bits with one character (95 combinations) to 78 bits with twelve characters (540 sextillion combinations).

 

 

Avoid creating a passphrase using popular phrases or recognizable sentences as these 'brain wallets’ are easy to predict. For a minimum recommended level of complexity (at least 64 bits of entropy), use at least:

 

- 6 random words from the BIP39 pre-determined word list

- 4 random words from a standard English dictionary

- 10 random characters from the ASCII character list

 

Theoretically, even if your 24 seed words are exposed, a strong passphrase can keep your Bitcoin account safe from brute-force attacks for hundreds of years.

 

 

Keep your seed words and passphrases in separate, secure locations. Always test your wallet with a small amount of funds before depositing larger amounts. Remember, the strength of your passphrase plays a vital role in the security of your Bitcoin wallet.

 

For a detailed understanding, check out the original article [here](https://www.bitplates.com/how-secure-is-your-passphrase).

 

This blog post is based on information from BitPLATES® as of 2022. Please seek up-to-date advice before acting on this information.