Multisignature (multisig) is a transaction method that requires multiple private keys in order to authorize the transaction. Users can define arbitrary requirements of M-of-N signatures to execute a valid transaction; for example, a 2-of-2 multisig is required to close payment channels in the Lightning Network, requiring both keys to sign the transaction. By distributing responsibility across multiple keys, users can achieve a greater level of security over single signature transactions, which are the default for Bitcoin. Many cold storage approaches use multisig. Shamir's Secret Sharing is a software implementation of multisig.