  Mobile code based computing requires development of protection schemes that
allow digital signature and encryption of data collected by the agents in
untrusted hosts. These algorithms could not rely on carrying encryption keys if
these keys could be stolen or used to counterfeit data by hostile hosts and
agents. As a consequence, both information and keys must be protected in a way
that only authorized hosts, that is the host that provides information and the
server that has sent the mobile agent, could modify (by changing or removing)
retrieved data. The data management model proposed in this work allows the
information collected by the agents to be protected against handling by other
hosts in the information network. It has been done by using standard public-key
cryptography modified to support protection of data in distributed environments
without requiring an interactive protocol with the host that has dropped the
agent. Their significance stands on the fact that it is the first model that
supports a full-featured protection of mobile agents allowing remote hosts to
change its own information if required before agent returns to its originating
server.
