What is multisig? (multi-signature)

What multisig means

Most bitcoin wallets are single-signature wallets: one key controls everything. If that key is lost or stolen, access to the bitcoin is gone.

Multisig (requiring more than one key to authorize a transaction) removes that single point of failure. A multisig vault holds multiple keys, and a transaction can only be sent when a minimum number of them sign it together.

This minimum is called the signing quorum (the minimum number of keys required to send bitcoin). Multisig setups are described using m-of-n notation, where n is the total number of keys and m is the quorum required to sign. For example, a 2-of-3 setup has 3 keys and requires any 2 of them to authorize a transaction.

How multisig works in your Casa vault

If you are a Standard member your Casa vault is a 3-key vault. Three keys protect your vault, and a signing quorum of 2-of-3 is required to send bitcoin. Losing one key does not affect your ability to access your vault, you still have two remaining keys to meet quorum.

If you are a Premium or Private Client member your Casa vault is a 5-key vault. Five keys protect your vault, and a signing quorum of 3-of-5 is required to send bitcoin. You can lose up to two keys without losing access to your vault.

Why multisig is more secure than a single-signature wallet

With a single-signature wallet, an attacker only needs to compromise one key to take everything. With multisig, they would need to compromise multiple keys simultaneously — keys that are stored in different locations and on different devices.

The same logic applies to accidents. If one hardware device fails, is lost, or is destroyed, your bitcoin in your Casa vault is unaffected because the remaining keys still meet quorum. You can then perform a key rotation (the process of replacing one key in the vault with a new one) using your remaining keys to restore a full set.

Casa's non-custodial approach to multisig

Casa is non-custodial. This means you hold your own keys, Casa cannot access your bitcoin on your behalf. In a 3-key vault, one of your three keys is the Casa Recovery Key (the key Casa holds offline on your behalf). Casa holds this key offline as a backup service, but it cannot move bitcoin from your vault unilaterally. Any transaction still requires your signing quorum, which includes your keys.

This is different from a custodial service, where a company holds your bitcoin for you. With Casa, the bitcoin in your vault is always controlled by your keys.

Casa vault options

To learn more about each vault type:

• Standard - 3-key vault

• Premium - 5-key vault