2-of-2

2-of-2 multisig offers some resistance against theft, but it increases the risk of key loss to unacceptable levels. If any one key is lost, the user's funds will also be lost. Duplicating or key-splitting one of the keys in a 2-of-2 setup can offer improved usability, but the system is still weak against disasters and attacks compared to a 2-of-3 or 3-of-5 scheme.