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Multisig | Bitcoin Glossary | Mapping Bitcoin

Multisig

Security

Also known as: multi-signature, multisignature

A Bitcoin transaction authorization scheme that requires multiple private keys to sign a transaction, expressed as M-of-N (e.g., 2-of-3 means 2 signatures from 3 possible keys). Multisig enhances security by eliminating single points of failure.

Overview

Multisig (multi-signature) is a Bitcoin feature that requires more than one private key to authorize a transaction. Expressed as M-of-N, where M is the number of required signatures and N is the total number of possible signers, multisig eliminates single points of failure in key management and is widely used for securing significant amounts of bitcoin.

Common Configurations

┌─────────────┬────────────────────────────────────┐
│ Configuration│ Use Case                          │
├─────────────┼────────────────────────────────────┤
│   1-of-2    │ Shared access (either party)       │
│   2-of-2    │ Mutual agreement required          │
│   2-of-3    │ Standard security (most popular)   │
│   3-of-5    │ Corporate treasury / high security │
└─────────────┴────────────────────────────────────┘

2-of-3 Example:
  Key A (hardware wallet)  ──┐
  Key B (mobile device)    ──┼── Any 2 can sign
  Key C (cold backup)     ──┘

How It Works

Traditional multisig uses the OP_CHECKMULTISIG opcode in Bitcoin Script. The locking script specifies the required number of signatures and the public keys of all possible signers. To spend, the required number of valid signatures must be provided in the unlocking script.

Multisig Address Types

  • P2SH Multisig: Wraps the multisig script in a P2SH address (starts with 3)
  • P2WSH Multisig: Native SegWit multisig (starts with bc1q, longer format)
  • P2TR/MuSig: Taproot with MuSig allows multisig that looks like a single signature on-chain, improving privacy and reducing fees

Security Benefits

Multisig protects against several failure modes: theft of a single key, loss of a single key, compromise of a single device, and coercion of a single individual. A 2-of-3 setup means losing one key is not catastrophic (the other two can still sign) and stealing one key is insufficient to move funds.

Common Misconceptions

Multisig does not hide the number of signers on-chain (except with MuSig/Taproot). Traditional P2SH or P2WSH multisig reveals the M-of-N configuration and all public keys when funds are spent. This is one reason the Taproot upgrade and Schnorr-based multisig schemes are significant privacy improvements.

Related Terms

2-of-3 MultisigSecurity

A multi-signature configuration that requires two out of three private keys to authorize a Bitcoin transaction. This setup is commonly used for shared custody, escrow arrangements, and enhanced security where no single party has full control over the funds.

Key PairCryptography

A mathematically linked pair of cryptographic keys: a private key (kept secret) used to sign transactions and a public key (shared openly) used to verify signatures and derive addresses. The private key can generate the public key but not vice versa.

P2SHProtocol

Pay-to-Script-Hash, a transaction type where the output is locked to the hash of a script rather than a public key hash. P2SH addresses start with '3' and enable complex spending conditions like multisig without the sender needing to know the details.

MuSigCryptography

A Schnorr-based multi-signature scheme that allows multiple signers to produce a single aggregate signature that looks identical to a regular single-key signature on-chain. MuSig improves privacy and reduces transaction size compared to traditional multisig.