Composite keys are useful in multiple scenarios. For example, assets can be placed under the control of a 2-of-2 composite key where one leaf key is owned by a user, and the other by an independent risk analysis system. The risk analysis system refuses to sign if the transaction seems suspicious, like if too much value has been transferred in too short a time window. Another example involves encoding corporate structures into the key, allowing a CFO to sign a large transaction alone but his subordinates are required to work together. Composite keys are also useful for notaries. Each participant in a distributed notary is represented by a leaf, and the threshold is set such that some participants can be offline or refusing to sign yet the signature of the group is still valid.