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The use of embedded block memories (BRAMs) in Xilinx FPGA devices makes it possible to store the T-Boxes that are employed to implement the AES block cipher’s SubBytes and MixColumns operations. Several studies into BRAM resistance to side-channel attacks have been reported in the literature, whereas this paper presents a novel attack based on tampering the BRAMs storing the T-Boxes. This approach allows recovering the key using a ciphertext-only attack for all AES key sizes. The complexity of the attack makes it completely feasible. The attack was mounted against previously reported FPGA-based AES implementations, taking into account the different design criteria used in each case and focusing mainly on the implementation of the final round of the AES algorithm, which plays a crucial role in the analysis. Three different final round implementations extracted from well-known existing architectures are analyzed in this work. The paper also discusses some countermeasures with regard to security, performance and FPGA resource utilization. The attack is presented against FPGA-based implementations but it can be extended to software architectures as well.

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T-box genes encode transcription factors involved in morphogenesis and organogenesis of vertebrates and invertebrates. Mutations in human T-box genes TBX3, TBX5, and TBX1 cause severe genetic disorders known as Ulnar-Mammary syndrome (UMS), Holt-Oram syndrome (HOS), and DiGeorge syndrome, respectively. The crystal structure of the T-box domain of the first human T-box transcription factor, TBX3, in complex with DNA at 1.7 Å resolution explains structural consequences of T-box domain point mutations observed in UMS and HOS patients. Comparison with the structure of the T-box domain from Xenopus laevis (Xbra) bound to DNA shows differences in several secondary structure elements and in the quaternary structure of the two complexes. TBX3 independently recognizes the two binding sites present in the palindromic DNA duplex, whereas in Xbra, binding to the palindrome is stabilized through interactions between the two monomers. The different quaternary structures suggest different DNA binding modes for T-box transcription factors.