How to safeguard your Bitcoin seed phrase

Your seed phrase is a universal backup to your coins, keeping it safe is a crucial part of managing and securing your funds in case your wallet is inaccessible.

How does a seed phrase work?

BIP39 describes the process of generating a mnemonic sentence that is later used to generate master seed key by randomly selecting between 12 and 24 numbers in the range of 0–2047. Each number represents an index to a word in a preset word list of 2048 words from the English dictionary (other languages are supported as well). These index numbers are then used to generate a master key and the user is eventually presented with the mnemonic sentence or seed phrase. As long as the user backs up these list of words in the correct order, he will always be able to recover his funds as all private keys are generated from the master seed. A cool feature that is usually missed when reviewing the mechanics of a seed phrase is the fact that all words in the dictionary can be identified uniquely by the first 4 characters, making it easier to type in hardware wallets where you sometimes need to use a small touch pad and also makes it harder to misspell longer words.

If a list of 12 words from a known 2048 words dictionary sounds like a small set to randomly select such an important key from, then that’s because humans are really bad at imagining just how big, big numbers are.

If I gave someone my first 6 words of my seed phrase in the correct order, he would still need to go over a key space of 2048⁶ combinations, which is: 73,786,976,294,838,206,464 options. Even if we could compute 100 billion guesses per second it will still take us over 23 years to go over the entire key space and cover all possible combinations. And that’s for a single mnemonic which we had the first 6 words for.

Pen and paper

As easy as it sounds, a pen and a piece of paper are the minimal approach to storing your seed phrase, it’s very common and offers a highly secured backup.

Pros

1. Secure, no one can access a piece of paper remotely.
2. Free

Cons

1. Can be easily destructed.
2. Easy to lose.

Possible improvements

1. If a 24 seed phrase is used, you could split the words into 3 parts. Part A holds words in positions 1–16, part B holds 9–24, part C holds 1–8 and 17–24. Make several copies and divide between people you trust. Each two shares can recover the full phrase.
2. A better, yet more complex approach to the above is to use Shamir Secret Sharing Scheme to split the mnemonics to m-of-n shares. This allows you to control the recovery threshold.
3. Split the words to several locations, make multiple copies of each.
4. Make several copies.
5. Laminate to avoid water damage.
6. Set a passphrase, store it in another location.

Physical device

Over the past few years, a lot of new physical devices have been brought to market that offers a serious upgrade over the pen and paper solution in terms of durability. These devices usually allow you to engrave your seed phrase onto a metal plate therefore provides the same security as a piece of paper, but with additional durability. If this approach works best for you, I suggest reviewing Jameson Lopp’s thorough testing of such solutions.

Pros

1. Secure, no one can remotely access a metal sheet.
2. Extremely durable against fire, corrosion and other physical damage.

Cons

1. Not free

Possible improvements

1. Purchase a few devices, split to different locations.
2. Add a passphrase, don’t include it on the metal sheet.
3. Not an improvement, but a very cheap and solid alternative to be considered can be found here

In the cloud

Some suggest that the best approach is to use a simple text file while encrypting it with a strong password, then storing it in your Google Drive, Dropbox or any other cloud provider (even multiple ones).

Pros

1. Secure, encrypted with a strong password using strong encryption.
2. Should be accessible for many years, practically indestructible.

Cons

1. Typing your seed phrase into any electronic device instantly reduces the security level of the seed phrase.
2. You now need to store/memorize your password for the encrypted file.

Possible improvements

1. Use multiple cloud providers.
2. Use strong encryption and a strong password, be very careful to use a password you will also remember.

Memorization

Some people feel that the safest place for their fortune is in their own minds, and there are ways to either memorize your seed phrase words or even memorize their index positions in the wordlist, turning the thing you need to remember from words into a long list of numbers.

Pros

1. Secure, no one can remotely access your mind (yet).

Cons

1. You will probably forget it.
2. Surely, you’ll forget it, don’t do this.

Possible improvements

1. None, don’t do it.

Need help recovering your seed phrase?

We at Brute Brothers have special software and hardware to help recover partial seed phrases for all wallet types. Contact us at sos@brutebrothers.com (PGP) for more details.