Bitcoin over Tor isn't a good idea

Bitcoin is a decentralized P2P digital currency in which coins are generated by a distributed set of miners and transaction are broadcasted via a peer-to-peer network. While Bitcoin provides some level of anonymity (or rather pseudonymity) by encouraging the users to have any number of random-looking Bitcoin addresses, recent research shows that this level of anonymity is rather low. This encourages users to connect to the Bitcoin network through anonymizers like Tor and motivates development of default Tor functionality for popular mobile SPV clients. In this paper we show that combining Tor and Bitcoin creates an attack vector for the deterministic and stealthy man-in-the-middle attacks. A low-resource attacker can gain full control of information flows between all users who chose to use Bitcoin over Tor. In particular the attacker can link together user's transactions regardless of pseudonyms used, control which Bitcoin blocks and transactions are relayed to the user and can \ delay or discard user's transactions and blocks. In collusion with a powerful miner double-spending attacks become possible and a totally virtual Bitcoin reality can be created for such set of users. Moreover, we show how an attacker can fingerprint users and then recognize them and learn their IP address when they decide to connect to the Bitcoin network directly.Comment: 11 pages, 4 figures, 4 table

Security Threats Classification in Blockchains

Blockchain, the foundation of Bitcoin, has become one of the most popular technologies to create and manage digital transactions recently. It serves as an immutable ledger which allows transactions take place in a decentralized manner. This expeditiously evolving technology has the potential to lead to a shift in thinking about digital transactions in multiple sectors including, Internet of Things, healthcare, energy, supply chain, manufacturing, cybersecurity and principally financial services. However, this emerging technology is still in its infancy. Despite the huge opportunities blockchain offers, it suffers from challenges and limitation such as scalability, security, and privacy, compliance, and governance issues that have not yet been thoroughly explored and addressed. Although there are some studies on the security and privacy issues of the blockchain, they lack a systematic examination of the security of blockchain systems. This research conducted a systematic survey of the security threats to the blockchain systems and reviewed the existing vulnerabilities in the Blockchain. These vulnerabilities lead to the execution of the various security threats to the normal functionality of the Blockchain platforms. Moreover, the study provides a case-study for each attack by examining the popular blockchain systems and also reviews possible countermeasures which could be used in the development of various blockchain systems. Furthermore, this study developed taxonomies that classified the security threats and attacks based on the blockchain abstract layers, blockchain primary processes and primary business users. This would assist the developers and businesses to be attentive to the existing threats in different areas of the blockchain-based platforms and plan accordingly to mitigate risk. Finally, summarized the critical open challenges, and suggest future research directions