Analysis and Probing of Parallel Channels in the Lightning Network

Abstract

Bitcoin can process only a few transactions per second, which is insufficient for a global payment network. The Lightning Network (LN) aims to address this challenge. The LN allows for low-latency bitcoin transfers through a network of payment channels. In contrast to regular Bitcoin transactions, payments in the LN are not globally broadcast. Thus it may improve not only Bitcoin's scalability but also privacy. However, the probing attack allows an adversary to discover channel balances, threatening users' privacy. Prior work on probing did not account for the possibility of multiple (parallel) channels between two nodes. Naive probing algorithms yield false results for parallel channels. In this work, we develop a new probing model that accurately accounts for parallel channels. We describe jamming-enhanced probing that allows for full balance information extraction in multi-channel hops, which was impossible with earlier probing methods. We quantify the attacker's information gain and propose an optimized algorithm for choosing probe amounts for multi-channel hops. We demonstrate its efficiency based on real-world data using our own probing-focused LN simulator. Finally, we discuss countermeasures such as new forwarding strategies, intra-hop payment split, rebalancing, and unannounced channels.

Revelio: A Network-Level Privacy Attack in the Lightning Network

“…We first collected the addresses of all LN nodes by taking a snapshot of the entire LN topology on 29 June 2022 using an lnd client and its built-in describegraph command. Because all LN nodes share the identical view of the LN topology most of the time, taking a topology snapshot from a single node is sufficient, as demonstrated in previous works (e.g., [12], [20], [81]). This snapshot, which also is used throughout this paper, consists of 17,644 nodes in its most significant connected component and 80,932 channels in total.…”

“…For example, the adversary can specifically target popular services, such as podcasts, streaming, or social apps, that publicly announce their payment amounts. Moreover, Revelio adversaries can launch channel probing attacks [12], [20], [71], [81] to monitor the balance of all channels. Yet, such an attack requires having LN nodes sending actual payments, and it may cost several thousand dollars for every probing.…”

“…Since LN is permissionless, an attacker can easily create many nodes in the LN topology and observe a large portion of multi-hop payments forwarded by them. This weakness has been the root causes of several existing attacks that deanonymize payment endpoints [59], [66], or channel balances [12], [20], [71], [81].…”

“…Aiming to learn the channel balances (e.g., that lead to large-scale payment deanonymization [34]), several probing attacks have been proposed. The strategies include sending payments through that channel that trigger failures [31], [53], [71], [81], sending payments only between adversarial nodes [20], [34], and jamming the channels when nodes have multiple channels in parallel [12].…”

A Review of the Lightning Network’s Evolution: Unraveling Its Present State and the Emergence of Disruptive Digital Business Models

“…With respect to privacy, Ref. [55] develop a new probing model that accounts for parallel channels and propose jamming-enhanced probing to extract full balance information. They also discuss potential countermeasures such as new forwarding strategies, intra-hop payment split, rebalancing and unannounced channels.…”