Tithonus: A Bitcoin Based Censorship Resilient System

Abstract

Providing reliable and surreptitious communications is difficult in the presence of adaptive and resourceful state level censors. In this paper we introduce Tithonus, a framework that builds on the Bitcoin blockchain and network to provide censorship-resistant communication mechanisms. In contrast to previous approaches, we do not rely solely on the slow and expensive blockchain consensus mechanism but instead fully exploit Bitcoin's peer-to-peer gossip protocol. We develop adaptive, fast and cost effective data communication solutions that camouflage client requests into inconspicuous Bitcoin transactions. We propose solutions to securely request and transfer content, with unobservability and censorship resistance, and free, pay-peraccess and subscription based payment options. When compared to state-of-the-art Bitcoin writing solutions, Tithonus reduces the cost of transferring data to censored clients by 2 orders of magnitude and increases the goodput by 3 to 5 orders of magnitude. We show that Tithonus client initiated transactions are hard to detect, while server initiated transactions cannot be censored without creating split world problems to the Bitcoin blockchain.

Utilizing Public Blockchains for Censorship-Circumvention and IoT Communication

“…Therefore, the cost of transmitting 1MB of data via Skywhisper is ≈ $0.05. This is much lower compared to similar techniques Tithonous [30] and R3C3 [24], where transmitting 1MB through Tithonous costs ≈ $83, and ≈ $6.8 in R3C3. 3 Security and Robustness.…”

“…On the other hand, it is provably secure that no censors can distinguish steganographically-subverted blockchain transactions; hence, they can not launch any targeted DoS attack against Skywhisper unless they blacklist the whole blockchain network which might have other financial ramifications. Besides, other content-insertion approaches that replace segments of the transactions, as done in Tithonus [30] and Catena [34], are susceptible to policy changes where certain transactions, or scripts, become conspicuous or are no longer accepted, forcing the adoption of alternative techniques.…”

“…2) Blockchain-based censorship circumvention. Tithonus [30], for example, offers a Bitcoin-based censorship-resistant system. Also, Catena [34] is an application that uses Bitcoin OP RETURN transactions to establish consensus among users on an application-specific log.…”

MoneyMorph: Censorship Resistant Rendezvous using Permissionless Cryptocurrencies

“…MoneyMorph (BTC) suffers from two limitations: (i) it requires to burn coins; and (ii) forces the censored user to prepare a spendable input with the precise value amount to generate transactions tx 1 and tx 2 . These two limitations can be mitigated by using the Pay2Multisig script in the encoding (as explained earlier in this section and similarly used in the community [59]), or adding an extra output as a change address. Both mitigations come at the cost of reducing the number of sibling transactions.…”

“…Concurrently to this work, Tithonus [59] contributed a censorship-resistant communication tool that leverages the Bitcoin blockchain and the Bitcoin P2P network to enable communication between the censored and uncensored areas. While Tithonus only considers Bitcoin as the communication channel, we instead define how to leverage other cryptocurrencies for rendezvous.…”