Breaking ACORN at Bitstream Level

Assuring the security of the Internet of Things (IoT) is much more challenging than assuring the security of centralized environments, like the cloud. A reason for this is that IoT devices are often deployed in domains that are remotely managed and monitored. Thus, they cannot be protected from physical attacks as reliably as data centers. Up till now, implementations of many established, standardized algorithms including AES and SNOW 3G have been broken by physical attacks. In this paper, we show that even the most recently designed algorithms are also vulnerable. We attack an SRAM-based FPGA implementation of ACORN v3 stream cipher, a finalist of CAESAR cryptographic competition for authenticated encryption. By modifying the content of several look-up tables directly in the bitstream, we inject faults which reduce the nonlinear feedback function of ACORN to a linear one. As a result, it becomes possible to extract the full key from 2
^15.34
bits of faulty keystream by an algebraic attack using 2
^35.46
operations. Our results, once again confirm the necessity to rethink the way cryptographic algorithms are implemented in FPGAs.