Negotiation among multiple agents remains an important topic of research in Distributed Artificial Intelligence (DAI). Most previous work on this subject, however, has focused on bilateral negotiation, deals that are reached between two agents. There has also been research on n-agent agreement which has considered "consensus mechanisms" (such as voting), that allow the full group to coordinate itself. These group decision-making techniques, however, assume that the entire group will (or has to) coordinate its actions. Sub-groups cannot make sub-agreements that exclude other members of the group. In some domains, however, it may be possible for beneficial agreements to be reached among sub-groups of agents, who might be individually motivated to work together to the exclusion of others outside the group. This paper considers this more general case of n-agent coalition formation. We present a simple coalition formation mechanism that uses cryptographic techniques for subadditive Task Oriented Domains. The mechanism is efficient, symmetric, and individual rational. When the domain is also concave, the mechanism also satisfies coalition rationality.