Branimir Pervan

selected publications

1. Energy-efficient distributed password hash computation on heterogeneous embedded system

   Pervan, Branimir, Knezović, Josip,  and Guberović, Emanuel

   Automatika 2022

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   This paper presents the improved version of our cool Cracker cluster (cCc), a heterogeneous distributed system for parallel and energy-efficient bcrypt password hash computation. The cluster consists of up to 8 computational units (nodes) with different performances measured in bcrypt hash computations per second [H/s]. In the cluster, nodes are low-power heterogeneous embedded systems with programmable logic containing specialized hash computation accelerators. In the experiments, we used a combination of Xilinx Zynq-series SoC boards and ZTEX 1.15y board which was initially used as a bitcoin miner. Zynq based nodes use the improved version of our custom bcrypt accelerator, which executes the most costly parts of the bcrypt hash computation in programmable logic. The cluster was formed around the famous open-source password cracking software package John the Ripper (abbr. JtR). On the communication layer, we used Message Passing Interface (MPI)library with a standard Ethernet network connecting the nodes. To mitigate the different performances among the cluster nodes and to balance the load, we developed and implemented password candidate distribution scheme based on the passwords’ probability distribution, i.e. the order of appearance in the dictionary. We tested individual nodes and the cluster as a whole, trying different combinations of nodes and evaluating our distribution scheme for password candidates. We also compared our cluster with various GPU implementations in terms of performance, energy-efficiency, and price-efficiency. We show that our solution outperforms other platforms such as high-end GPUs, by a factor of at least 3 in terms of energy-efficiency and thus producing less overall cost of password attack than other platforms. In terms of the total operational costs, our cluster pays off after 4500 cracked passwords for a bcrypt hash with cost parameter 12, which makes it more appealing for real-world password-based system attacks. We also demonstrate the scalability of our cCc cluster.

   @article{Pervan2022,
     author = {Pervan, Branimir and Knezovi{\'{c}}, Josip and Guberovi{\'{c}}, Emanuel},
     doi = {10.1080/00051144.2022.2042115},
     journal = {Automatika},
     number = {3},
     pages = {399--417},
     publisher = {Taylor & Francis},
     title = {{Energy-efficient distributed password hash computation on heterogeneous embedded system}},
     url = {https://www.tandfonline.com/doi/abs/10.1080/00051144.2022.2042115},
     volume = {63},
     year = {2022},
   }

2. Distributed Password Hash Computation on Commodity Heterogeneous Programmable Platforms

   Pervan, Branimir, Knezovic, Josip,  and Pericin, Katja

   In 13th USENIX Workshop on Offensive Technologies, WOOT 2019, co-located with USENIX Security 2019 2019

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   In this paper, we present the Cool Cracker Cluster cCc: a heterogeneous distributed system for parallel, energy-efficient, and high-speed bcrypt password hash computation. The cluster consists of up to 32 heterogeneous nodes with Zynq-7000-based SoCs featuring a dual-core, general-purpose ARM processor coupled with FPGA programmable logic. Each node uses our custom bcrypt accelerator which executes the most costly parts of the hash computation in programmable logic. We integrated our bcrypt implementation into John the Ripper, an open source password cracking software. Message Passing interface (MPI) support in John the Ripper is used to form a distributed cluster. We tested the cluster, trying different configurations of boards (Zedboards and Pynq boards), salt randomness, and cost parameters finding out that password cracking scales linearly with the number of nodes. In terms of performance (number of computed hashes per second) and energy efficiency (performance per Watt), cCc outperforms current systems based on high-end GPU cards, namely Nvidia Tesla V100, by a factor of 2.72 and 5 respectively.

   @inproceedings{Pervan2019,
     author = {Pervan, Branimir and Knezovic, Josip and Pericin, Katja},
     booktitle = {13th USENIX Workshop on Offensive Technologies, WOOT 2019, co-located with USENIX Security 2019},
     title = {{Distributed Password Hash Computation on Commodity Heterogeneous Programmable Platforms}},
     year = {2019},
   }