Cosigner

A Cosigner is one of multiple parties in a multisig wallet who signs transactions with their private key. All required cosigners must approve before the transaction executes. Also known as a multisig participant or signing party.

Cosigners work in multisignature (multisig) setups. Wallet creators define a threshold, such as 2-of-3. This means two out of three cosigners must sign. Each cosigner uses their own private key on separate devices, like hardware wallets. The wallet coordinates partial signatures. It combines them into a full transaction signature only when the threshold meets.

For example, in a 2-of-3 multisig, Alice, Bob, and Charlie hold keys. To spend funds, any two sign. Alice proposes the transaction. Bob reviews and signs. Charlie does not need to act. The network verifies the valid signature and processes it.

Cosigners boost security. They prevent single-key theft or loss from compromising funds. Businesses use them for treasury management. Families apply them for shared inheritance wallets. This distributes trust across parties.

Key traits include independence—each cosigner controls their key. They support hardware wallets for offline signing. Cosigners operate in Bitcoin, Ethereum, and other blockchains with multisig standards like P2SH or P2WSH.