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See detailAnalysis and Probing of Parallel Channels in the Lightning Network
Biryukov, Alexei UL; Naumenko, Gleb; Tikhomirov, Sergei UL

E-print/Working paper (2021)

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 ... [more ▼]

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 N-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. [less ▲]

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See detailAutomated Truncation of Differential Trails and Trail Clustering in ARX
Biryukov, Alexei UL; Cardoso Dos Santos, Luan UL; Feher, Daniel UL et al

E-print/Working paper (2021)

We propose a tool for automated truncation of differential trails in ciphers using modular addition, bitwise rotation, and XOR (ARX). The tool takes as input a differential trail and produces as output a ... [more ▼]

We propose a tool for automated truncation of differential trails in ciphers using modular addition, bitwise rotation, and XOR (ARX). The tool takes as input a differential trail and produces as output a set of truncated differential trails. The set represents all possible truncations of the input trail according to certain predefined rules. A linear-time algorithm for the exact computation of the differential probability of a truncated trail that follows the truncation rules is proposed. We further describe a method to merge the set of truncated trails into a compact set of non-overlapping truncated trails with associated probability and we demonstrate the application of the tool on block cipher Speck64. We have also investigated the effect of clustering of differential trails around a fixed input trail. The best cluster that we have found for 15 rounds has probability 2^−55.03 (consisting of 389 unique output differences) which allows us to build a distinguisher using 128 times less data than the one based on just the single best trail, which has probability 2^−62. Moreover, we show examples for Speck64 where a cluster of trails around a suboptimal (in terms of probability) input trail results in higher overall probability compared to a cluster obtained around the best differential trail. [less ▲]

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See detailCryptanalysis of a Dynamic Universal Accumulator over Bilinear Groups
Biryukov, Alexei UL; Udovenko, Aleksei UL; Vitto, Giuseppe UL

in Topics in Cryptology – CT-RSA 2021 (2021)

In this paper we cryptanalyse the two accumulator variants proposed by Au et al., which we call the alpha-based construction and the common reference string-based (CRS-based) construction. We show that if ... [more ▼]

In this paper we cryptanalyse the two accumulator variants proposed by Au et al., which we call the alpha-based construction and the common reference string-based (CRS-based) construction. We show that if non-membership witnesses are issued according to the alpha-based construction, an attacker that has access to multiple witnesses is able to efficiently recover the secret accumulator parameter alpha and completely break its security. More precisely, if p is the order of the underlying bilinear group, the knowledge of O(log p log log p) non-membership witnesses permits to successfully recover alpha. Further optimizations and different attack scenarios allow to reduce the number of required witnesses to O(log p), together with practical attack complexity. Moreover, we show that accumulator's collision resistance can be broken if just one of these non-membership witnesses is known to the attacker. We then show how all these attacks for the alpha-based construction can be easily prevented by using instead a corrected expression for witnesses. Although outside the original security model assumed by Au \etal but motivated by some possible concrete application of the scheme where the Manager must have exclusive rights for issuing witnesses (e.g. white/black list based authentication mechanisms), we show that if non-membership witnesses are issued using the CRS-based construction and the CRS is kept secret by the Manager, an attacker accessing multiple witnesses can reconstruct the CRS and compute witnesses for arbitrary new elements. In particular, if the accumulator is initialized by adding m secret elements, the knowledge of m non-membership witnesses allows to succeed in such attack. [less ▲]

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See detailDynamic Universal Accumulator with Batch Update over Bilinear Groups
Vitto, Giuseppe UL; Biryukov, Alexei UL

E-print/Working paper (2021)

Detailed reference viewed: 30 (1 UL)
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See detailDummy Shuffling Against Algebraic Attacks in White-Box Implementations
Biryukov, Alexei UL; Udovenko, Aleksei UL

in Canteaut, Anne; Standaert, Francois-Xavier (Eds.) Advances in Cryptology -- EUROCRYPT 2021 (2021)

Detailed reference viewed: 53 (0 UL)