We propose a cryptographic protocol for the secure and efficient acknowledgment of peer-to-peer multicast messages. Every node is capable of verifying the acknowledgments upon receiving them, without waiting for and relying on the server. Our protocol is efficient as it is bounded by the maximum depth of the tree, and is resistant to denial-of-service attacks.

Through the use of less costly symmetric cryptographic operations such as MAC and symmetric ciphers, we are able to create resistance against denial-of-service attacks and spoofing of network packet source. Compared to other protocols, our protocol has made the trade-off of requiring the server to maintain the state of every node in the tree, and requiring every ancestor node to be notified of every joins and drops. In return, we obtain the ability to perform incremental verification of acknowledgments.