Secure Anonymous Acknowledgments in a Delay-Tolerant Network
Edoardo Biagioni · 2023
Acknowledgments are used in TCP and other protocols for reliable transmission of data. This paper describes a special kind of acknowledgment with additional features, including in particular a guarantee that only the intended receiver can issue a valid acknowledgment for a given message. Unlike TCP, these acknowledgements work well even for connectionless communications. This acknowledgement mechanism assumes that secure encryption is used to protect message data. The sender of a data message includes a randomly-generated acknowledgement in the encrypted part of the message. As long as only the intended receiver can decrypt the message, only the intended receiver can issue the acknowledgement when it receives the message. Such randomly-generated acknowledgments in no way identify senders and receivers, providing a degree of anonymity. In a Delay-Tolerant Network all hosts participate in forwarding data, taking on the role that routers fill in a more conventional network. Hosts cache messages for later delivery to other hosts that may be connected only intermittently. To keep caches manageable, messages must expire after a certain time. To further improve cache management, the cryptographic hash of each message acknowledgement is included as the message identifier in the unencrypted part of the message. A forwarding host that receives an acknowledgement can hash it and remove from its cache any message matching this message identifier, and decline to forward any future such messages.