Cryptology ePrint Archive: Report 2021/670

AOT: Anonymization by Oblivious Transfer

Farid Javani and Alan T. Sherman

Abstract: We introduce AOT, an anonymous communication system based on mix network architecture that uses oblivious transfer (OT) to deliver messages. Using OT to deliver messages helps AOT resist blending (n−1) attacks and helps AOT preserve receiver anonymity, even if a covert adversary controls all nodes in AOT. AOT comprises three levels of nodes, where nodes at each level perform a different function and can scale horizontally. The sender encrypts their payload and a tag, derived from a secret shared between the sender and receiver, with the public key of a Level-2 node and sends them to a Level-1 node. On a public bulletin board, Level-3 nodes publish tags associated with messages ready to be retrieved. Each receiver checks the bulletin board, identifies tags, and receives the associated messages using OT. A receiver can receive their messages even if the receiver is offline when messages are ready. Through what we call a "handshake" process, communicants can use the AOT protocol to establish shared secrets anonymously. Users play an active role in contributing to the unlinkability of messages: periodically, users initiate requests to AOT to receive dummy messages, such that an adversary cannot distinguish real and dummy requests.

Category / Keywords: cryptographic protocols / Anonymous communication, anonymous secret sharing, blending attack, mixnets, oblivious transfer

Date: received 22 May 2021

Contact author: javani1 at umbc edu, sherman at umbc edu

Available format(s): PDF | BibTeX Citation

Version: 20210525:070739 (All versions of this report)

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