Composed of a list of words, typically 12 or 24, the seed phrase is all that is needed to keep a backup of your wallet and, if necessary, restore it: how is it obtained?
Twelve or twenty-four words. In most cases, this is all that is needed to securely store one’s bitcoins. But it hasn’t always been this way.
In the early years of Bitcoin, the most common wallets were non–deterministic, consisting of a series of independently generated keys. For this reason, they were also called by the acronym JBOK: Just a Bunch of Keys. In these wallets, it was necessary to note and store the respective private key for each generated public key to recover one’s funds.
In 2012, deterministic wallets were introduced, and they remain the most widely used today. In this type of wallet, all private keys are derived from a single hexadecimal number called a seed. For example:
1d3d932b2f450a7746e9eca0d24d3ab98b210cdb7c14fdfbc59d34f4b16948b202f2ac70f003d6458cb735cfda2b5eed607a3f62664715fb0dc0c76bca4bac43
Unlike non-deterministic wallets, deterministic ones can regenerate the entire wallet solely from the seed. It is sufficient to save and store the seed to reconstruct the wallet at any time. It is not even necessary to note this long string of characters to have a backup of your wallet; 12 words are enough.
The Bitcoin community recognized the difficulty of remembering or saving such a complex number as the seed. The solution came in 2013 with BIP-39: a standard capable of converting the seed into a sequence of easily transcribable and memorable words, defined as a mnemonic seed phrase.
In the following example, starting from a hexadecimal entropy code, the mnemonic seed phrase is generated, from which the seed is obtained.
- Entropy (hexadecimal number): 4fca135d8f40accc85d01bb77f4667c4
- Mnemonic seed phrase: exist explain student burden approve green blanket address resist when okay maximum
- Seed: adf32eb08e21808ef677d0989c8bc6eee80842adaab2c0b773e8204220f389349066a6b5468282e2a021fcbd64d0c9e92a19954af9d791cf9380fba6fea325c2
To try other similar examples, you can use this website.
The longer the mnemonic seed phrase, the greater the protection of the wallet against brute force attacks.
This is because a 12-word mnemonic seed phrase is generated using 128 bits of entropy, while a 24-word seed phrase uses 256 bits. Entropy is a measure of the amount of uncertainty or randomness in a system. In terms of security, the higher the entropy, the more difficult it is to predict or guess the outcome.
Today, most wallets generate mnemonic seed phrases with 12 or 24 words, but it’s also possible to generate them with 15, 18, and 21 words.
