Bitcoin Self-Custody Step by Step: Seed Phrases, Multisig and Inheritance Planning

Step 1: Understand what you are protecting

Your coins sit on the blockchain. What you hold is the set of keys that can spend them. Those keys are generated from a recovery phrase, so the phrase is the thing to protect. Trezor describes it as "a list of words that can restore access to your crypto if your device is lost, damaged, or reset," and says that without it "your crypto cannot be recovered." Losing the device is therefore an inconvenience if the backup is safe. Losing the backup is a different matter.

The flip side is also true. Anyone who gets the words can restore your wallet on their own device. That is why scammers ask for them. Our scam checklist covers the usual approaches, and the rule there applies here: no real support team, exchange or wallet needs your seed phrase.

Step 2: Create and record the seed phrase

Most wallets follow BIP-39. The standard works like this, according to the Bitcoin Wiki's summary:

(The standard also defines 15-word and 21-word phrases.)

So a 12-word phrase carries 128 bits of real entropy, and the last word includes the checksum. That gives 2^128 valid phrases, about 3.4 × 10^38 (our calculation). A 24-word phrase carries 256 bits. Trezor devices use BIP-39 phrases of 12 or 24 words, depending on the model, and newer Trezor models also support a separate standard, SLIP-39, with 20-word shares.

The checksum has a practical use: wallet software should validate it and warn when a phrase is invalid. It is not a safety net, though. A 12-word phrase has only 4 checksum bits, so a random wrong phrase passes the check about 1 time in 16 (our calculation).

How to record it. From Trezor and Coldcard's guidance:

We did not find a vendor statement on photographs in the pages we reviewed. Our own advice is not to keep a digital copy at all, because anyone who gets into the account holding it can restore your wallet.

• The wallet generates random entropy of 128 to 256 bits.
• A checksum of one bit per 32 bits of entropy is added, taken from the SHA-256 hash of the entropy.
• The result is split into 11-bit groups, and each group selects a word from a list of 2,048 words.

1. Keep the backup offline, private and protected from damage or loss. That is Trezor's wording.
2. Never type the words into an app or website to check them. Trezor warns against this explicitly.
3. Use durable media. Coldcard's inheritance guide lists the seed phrase on durable media, with metal preferred.
4. Write the words in order and number them. This is our practical advice, not something we found in the sources.

Step 3: Decide whether to add a passphrase

A passphrase is an extra secret that is combined with the phrase. In BIP-39, the seed is derived using PBKDF2 with HMAC-SHA512 and 2,048 iterations. The salt is the word "mnemonic" plus the passphrase, and with no passphrase the empty string is used.

The consequence, stated in the Bitcoin Wiki: "every passphrase generates a valid seed." That works in two directions.

If you add one, treat it as a second backup with its own location and its own place in your inheritance instructions. A passphrase nobody knows about is the same as a lost wallet.

• Upside: someone who finds your words alone gets a different wallet from the one with your coins.
• Downside: if you mistype the passphrase, the wallet doesn't give an error. It opens a valid, empty wallet. Coldcard's inheritance guide adds that the passphrase must be stored separately from the seed and that having one without the other is not enough for access.

Step 4: Test recovery before you rely on it

Our suggestion: before you put significant funds in, restore the wallet from the backup, either on the same device after a reset or on a second device, and confirm the first receiving address matches. This catches a mis-copied word while a mistake costs nothing. Coldcard makes a related point for inheritance: a trusted person should attempt recovery on a test wallet, using only the written instructions, before real funds are at stake.

For a first transfer, send a small amount, then test spending it. This part is our suggestion.

Step 5: Consider multisig

In a single-signature wallet, one key spends. In an m-of-n multisig wallet, m of n keys must sign. Unchained, a multisig vendor, defines the 2-of-3 model as three keys of which any two can spend. Its points on the trade-offs:

Unchained sells collaborative-custody 2-of-3 vaults, and its article concludes that 2-of-3 strikes "the optimal balance for most people securing a material percentage of their wealth." That is a vendor's judgment about its own product category. The mechanics above are standard, but the recommendation is an opinion.

A reasonable test for whether multisig is worth it for you: can you reliably manage three seed phrases, a config file and a recovery procedure for years? More keys protect against theft and single failures, but each one adds something that can be lost.

• The higher the m, the more keys an attacker must control to move the funds.
• A 2-of-3 setup tolerates the loss of one key. A 3-of-5 setup tolerates more losses and gives more protection from theft, but it has ten keys and seed phrases to protect without a custodian, against six for 2-of-3, and its transactions are larger and cost more in fees.
• Recovery needs more than the keys. Unchained says you must keep the multisig configuration file with your keys, and Coldcard's guide says that without the wallet descriptor "the heir cannot reconstruct the wallet even with all the keys."
• "Losing any multisig keys or seed phrases is dangerous," in Unchained's words, and a lost key should be replaced as soon as the loss is noticed.

Step 6: Plan for inheritance

A will does not give anyone the keys. Coldcard puts it bluntly: "A will naming a beneficiary does nothing without the keys." Heirs need access plus instructions, and Coldcard observes that most holders have the first and not the second.

Its guide lists four approaches:

Coldcard sells hardware wallets and names Unchained and Casa as examples of collaborative custody. Read this as a map of options, not a ranking.

What your heirs need (from the same guide):

The guide says instructions matter as much as the keys. It also advises testing the plan with a trusted person, and consulting a qualified attorney on how wills, deposits and beneficiary designations interact with a bitcoin plan. We agree. Legal treatment varies by country, and none of the sources we used covers that.

• the seed phrase, on durable media;
• the passphrase, if you use one, stored separately;
• the wallet descriptor, for multisig;
• step-by-step recovery instructions written for a non-technical reader;
• a named technical contact who can help;
• the location of the hardware wallet, or confirmation that a compatible device can be used.

A checklist

This article is general information, not financial or legal advice.

1. Generate the phrase on the device. Write it down once, by hand, in order.
2. Use durable media and keep it offline. Never photograph it or type it into a website.
3. Decide on a passphrase. If you add one, store it separately and record where.
4. Restore the wallet from your backup and confirm the addresses match.
5. Test with a small amount before moving the rest.
6. Choose single-signature or multisig based on what you can manage. If multisig, store the config file or descriptor with your keys.
7. Write inheritance instructions for a non-technical reader, name a contact, and test them.
8. Review the plan once a year. People move, devices change and instructions go stale.