How low can you go? Using side-channel data to enhance brute-force key recovery

Side-channel analysis techniques can be used to construct key recovery attacks by observing a side-channel medium such as the power consumption or electromagnetic radiation of a device while is it performing cryptographic operations. These attack results can be used as auxiliary information in an enhanced brute-force key recovery attack, enabling the adversary to enumerate the most likely keys first. We use algorithmic and implementation techniques to implement a timeand memory-efficient key enumeration algorithm, and in tandem identify how to optimise throughput when bulk-verifying quantities of candidate AES-128 keys. We then explore how to best distribute the workload so that it can be deployed across a significant number of CPU cores and executed in parallel, giving an adversary the capability to enumerate a very large number of candidate keys. We introduce the tool labynkyr, developed in C++11, that can be deployed across any number of CPUs and workstations to enumerate keys in parallel. We conclude by demonstrating the effectiveness of our tool by successfully enumerating 2 AES-128 keys in approximately 30 hours using a modest number of CPU cores, at an expected cost of only 700 USD using a popular cloud provider.