Intro to Multisig

9 min readinteractiveIncludes quiz · 5 questions

Multisig (multi‑signature) means spending requires M out of N independent keys. Example: 2‑of‑3 means any 2 of 3 keys must sign. This removes single‑point failure and is great for large savings, teams, and inheritance.

Simple definitions (plain English):

  • •M‑of‑N: The threshold (M) of total keys (N) needed to spend.
  • •Key: A private key held on a device (hardware wallet, phone, paper).
  • •Cosigner: A person/device that holds one of the keys.
  • •Coordinator: Software that helps build transactions (e.g., Sparrow, Specter, BlueWallet). It never needs your seeds.
  • •PSBT: Partially Signed Bitcoin Transaction file passed between cosigners to collect signatures.
  • •Descriptor: A compact recipe that defines the multisig wallet (which keys and what script type, e.g., bc1q… P2WSH/P2TR).

Why it's safer:

  • •One lost or stolen key can't spend alone.
  • •Keys can be stored in different places (home safe, bank box, with attorney).
  • •Devices from different brands reduce one‑vendor risk.

Common configurations (examples):

  • •2‑of‑3: Popular for individuals and families—tolerates one loss.
  • •3‑of‑5: Popular for companies/DAOs—tolerates two losses.
  • •2‑of‑2: Both keys required—good for joint control but no fault tolerance.

How a spend works (step‑by‑step):

1) Coordinator builds a PSBT using your descriptor and UTXOs. 2) PSBT is shown on each signing device. 3) Each required device reviews and signs (on device screen). 4) Final signature set is combined and broadcast as a normal Bitcoin tx.

Backups you MUST keep (separately):

  • •Seed for each key: 12–24 words per device.
  • •Optional passphrase for each key (if enabled).
  • •Wallet descriptor + cosigner xpubs/fingerprints (export as a file or print).
  • •A written quorum note: e.g., “Savings Wallet: 2‑of‑3; Keys at Home Safe / Bank Box / Attorney.”

Setup options:

  • •Software coordinator: Sparrow, Specter, BlueWallet (multisig).
  • •Hardware devices: Mix vendors (e.g., Trezor + Ledger + Coldcard).
  • •Script type: Native SegWit (P2WSH) or Taproot multisig (P2TR) when supported.

Costs & trade‑offs:

  • •More devices to buy and manage.
  • •More steps when spending (collect multiple signatures).
  • •Higher address/tx size than single‑sig (slightly higher fees).
  • •Far better resilience against loss/theft.

When to use multisig:

  • •Long‑term savings (cold storage).
  • •Shared control (family, business, club).
  • •Inheritance planning with trusted parties.
  • •Regions with higher theft/coercion risk.

Common mistakes (avoid):

  • •Storing all keys in one place (defeats the purpose).
  • •Not backing up descriptor/cosigner info (harder recovery).
  • •Mixing all keys on one device/brand only.
  • •Forgetting a passphrase that was enabled on any key.

Quick start (2‑of‑3 example):

1) Pick three different hardware wallets (ideally different brands). 2) In a coordinator app, create a new 2‑of‑3 wallet and add each device's xpub. Save/print the descriptor and cosigner info. 3) Verify receive address on one device screen and do a small test deposit. 4) Build a PSBT to send the test amount out. Collect 2 signatures on devices and broadcast. 5) After success, fund the wallet and store each seed/backup in separate secure locations.

2‑of‑3 Example
2‑of‑3 Example

Test Your Knowledge

This lesson includes a 5-question quiz (passing score: 75%).

Quiz functionality available in the mobile app.