Paper 2018/454

R3C3: Cryptographically secure Censorship Resistant Rendezvous using Cryptocurrencies

Mohsen Minaei, Pedro Moreno-Sanchez, and Aniket Kate

Abstract

Cryptocurrencies and blockchains are set to play a major role in the financial and supply-chain systems. Their presence and acceptance across different geopolitical corridors, including in repressive regimes, have been one of their striking features. In this work, we leverage this popularity for bootstrapping censorship resistant (CR) communication. We formalize the notion of stego-bootstrapping scheme and formally describe the security notions of the scheme in terms of rareness and security against chosen-covertext attacks. We present R3C3, a Cryptographically secure Censorship-Resistant Rendezvous using Cryptocurrencies. R3C3 allows a censored user to interact with a decoder entity outside the censored region, through blockchain transactions as rendezvous, to obtain bootstrapping information such as a CR proxy and its public key. Unlike the usual bootstrapping approaches (e.g., emailing) with heuristic security if any, R3C3 employs public-key steganography over blockchain transactions to ensure cryptographic security, while the blockchain transaction costs may deter the entry-point harvesting attacks. We develop bootstrapping rendezvous over Bitcoin, Zcash, Monero and Ethereum as well as the typical mining process, and analyze their effectivity in terms of cryptocurrency network volume and introduced monetary cost. With its highly cryptographic structure, Zcash is an outright winner for normal users with 1168 byte bandwidth per transaction costing only 0.03 USD as the fee, while mining pool managers have a free, extremely high bandwidth rendezvous when they mine a block.