Cryptology ePrint Archive: Report 2020/248

Blinder: MPC Based Scalable and Robust Anonymous Committed Broadcast

Ittai Abraham and Benny Pinkas and Avishay Yanai

Abstract: Anonymous Committed Broadcast is a functionality that extends DC-nets and allows a set of clients to privately commit a message to set of servers, which can then simultaneously open all committed messages in a random ordering. Anonymity holds since no one can learn the ordering or the content of the client’s committed message.

We present Blinder, the first system that provides a scalable and fully robust solution for anonymous committed broadcast. Blinder maintains both properties of security (anonymity) and robustness (aka. ‘guaranteed output delivery’ or ‘availability’) in the face of a global active (malicious) adversary. Moreover, Blinder is censorship resistant, meaning that a honest client cannot be blocked from participating. Blinder obtains its security and scalability by carefully combining classical and state-of-the-art techniques from the fields of anonymous communication and secure multiparty computation (MPC).

In order to demonstrate scalability, we evaluate Blinder with up to 1 million clients, up to 100 servers and a message size of up to 10 kilobytes. In addition, we show that it is a perfect fit to be implemented on a GPU. A GPU based implementation of Blinder with 5 servers, which accepts 1 million clients, incurs a latency of less than 8 minutes; faster by a factor of > 100 than the 3-servers Riposte protocol (SOSP ’15), which is not robust and not censorship resistant; we get an even larger factor when comparing to AsynchroMix and PowerMix (CCS ’19), which are the only constructions that guarantee fairness (or robustness in the online phase).

Category / Keywords: cryptographic protocols / anonymity, broadcast,

Date: received 23 Feb 2020, last revised 23 Jul 2020

Contact author: ay yanay at gmail com

Available format(s): PDF | BibTeX Citation

Note: Moved all related works to the main body and adding a comparison to Loopix.

Version: 20200723:123508 (All versions of this report)

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