Bitcoin multisignature encodes an m-of-n condition: any m valid signatures from n designated public keys can authorize a spend. It reduces dependence on one key, but the exact script or descriptor, key order, derivation paths and recovery plan are part of the backup.
Multisig can distribute authority across people, devices or places so theft or loss of one signer need not move or destroy the funds. [Bitcoin Developer Guide — P2SH Multisig] [BIP 11 — M-of-N Standard Transactions] [BIP 67 — Deterministic key sorting] [BIP 383 — Multisig output descriptors]
The output commits to a threshold and public keys, commonly through a descriptor such as sortedmulti. Spending supplies enough valid signatures and the script data required by the output type. [Bitcoin Developer Guide — P2SH Multisig] [BIP 11 — M-of-N Standard Transactions] [BIP 67 — Deterministic key sorting] [BIP 383 — Multisig output descriptors]
No coordinator can forge a missing signature. Each signer should independently verify outputs, amounts and fees; copying the same compromised wallet view defeats the intended separation. [Bitcoin Developer Guide — P2SH Multisig] [BIP 11 — M-of-N Standard Transactions] [BIP 67 — Deterministic key sorting] [BIP 383 — Multisig output descriptors]
More signers add operational complexity, transaction weight and backup material. A bad threshold can make collusion too easy or recovery impossible. [Bitcoin Developer Guide — P2SH Multisig] [BIP 11 — M-of-N Standard Transactions] [BIP 67 — Deterministic key sorting] [BIP 383 — Multisig output descriptors]
Record the descriptor and key origins, test receive and recovery paths, separate devices and locations, and rehearse replacement of a lost signer before funding heavily. [Bitcoin Developer Guide — P2SH Multisig] [BIP 11 — M-of-N Standard Transactions] [BIP 67 — Deterministic key sorting] [BIP 383 — Multisig output descriptors]
A 2-of-3 spending policy
Three keys are created and stored in separate failure domains. Any two can authorize a transaction, so one lost key does not destroy access and one stolen key is insufficient to spend. The wallet policy or descriptor must also be backed up.
For the clearest picture, read this entry together with Private Key, Bitcoin wallet, PSBT. The reverse links also lead from HD Wallet, Cold Storage, Watch-only Wallet, Change output.
01Is multisig automatically safer than one hardware wallet?+
It can remove a single point of failure, but only if keys, backups, policy data and recovery procedures are genuinely separated and tested. Added complexity can create new failure modes.
02Do all multisig keys need to be in the same place to spend?+
No. Partially signed transactions allow signers to review and add signatures separately. Only the required threshold of valid signatures must be assembled before broadcast.