A new study conducted by consulting firm Trail of Bits and funded by the U.S. Defense Advanced Research Projects Agency (DARPA) concluded that despite claims to the contrary, blockchains are not impenetrable but can be subverted to dishonest means.
Despite the growing prevalence of blockchains and other examples of distributed ledger technology, researchers determined that the presumption of security provided by these systems’ lack of centralized control and supposedly unsusceptible nature to change was not all it appeared. While the systems’ cryptographic elements were more or less secure, bad actors had other options, such as simply subverting the properties of a blockchain’s implementation, networking, or consensus protocol.
“The report demonstrates the continued need for careful review when assessing new technologies, such as blockchains, as they proliferate in our society and economy,” Joshua Baron, DARPA program manager overseeing the study, said. “We should not take any promise of security on face value, and anyone using blockchains for matters of high importance must think through the associated vulnerabilities.”
The report scrolled through the fundamental properties of blockchains and examined associated cybersecurity risks. The holistic analysis showed that Bitcoin nodes, in particular, are a weak link.
“From our crawls of the Bitcoin network, we observe that 21 percent of Bitcoin nodes are running an old version of the Bitcoin Core client that is known to be vulnerable,” the report stated. “While software bugs can lead to consensus errors, we demonstrated that overt software changes can also modify the state of the blockchain. Therefore, the core developers and maintainers of blockchain software are a centralized point of trust in the system, susceptible to targeted attack. There are currently four active contributors with access to modify the Bitcoin Core codebase, the compromise of any of whom would allow for arbitrary modification of the codebase…The blockchain client implementation is not alone in its importance—the entire ecosystem of blockchain software poses a risk of consensus errors and differentials.”
In their conclusion, the report’s authors stated that a small segment of a blockchain’s participants could gain excessive, centralized control over the entire system. Bitcoin nodes were cited as especially incentivized to behave dishonestly, bolstered by a lack of known methods to create a permissionless blockchain impervious to malicious nodes without having an open computer network protocol for control systems, known as a Time-Triggered Protocol (TTP).
The report proposed a new metric for blockchain centrality based on nodes’ topological influence on consensus. Still, all protocol traffic is presently unencrypted and therefore susceptible to attacker-in-the-middle attacks – a particularly troublesome state for Bitcoin. Further, the authors concluded that software diversity in blockchains is another issue for upstream dependencies and patching concerns.