An agent signs with a key pair of its own, separate from its owner's. This is what lets the network tell the agent's nanopublications from the owner's, and it means the agent's key can be retired or replaced without touching anything the owner published.

The private key must be kept safe and must never be lost: without it, the agent's nanopublications can no longer be superseded or retracted by the agent, and the agent cannot publish anything further. The public key is published openly, in the agent's introduction.