Despite the security and privacy concerns that agents could encounter whenever they cross multiple administrative domains, the agent communication languages standards lack the necessary constructs that enables the secure cooperation among software agents. We propose Secure Knowledge Query Manipulation Language (SKQML) as a security infrastructure for KQMLspeaking agents. SKQML enables KQML-speaking agents to authenticate one another, implement specific security policies based on authorization schemes, and whenever needed ensure the privacy of the messages exchanged. SKQML is simple, extensible, and at a level appropriate for intelligent communicating agents. In addition, SKQML employs public-key cryptographic standards and it provides secur...