AN APPROACH TO NON-EQUIVALENT STEGANOGRAPHIC EMBEDDING OF ADDITIONAL DATA INTO THE PROGRAM CODE OF FPGA LUT UNITS

Purpose. To increase the effective volume of stego containers in the FPGA program code. To achieve this purpose, an additional procedure of non-equivalent transformations of FPGA program code is added. Non-equivalent transfor-mations complement the traditional procedure of equivalent transformations of program code. The joint use of these two types of transformations leads to the achievement of the purpose of this paper. Methodology. The steganographic ap-proach is used to covertly embed additional data into the FPGA chip program code. In this case the FPGA program code is a stego container. The stego container embedding procedure is used to perform hidden monitoring of the FPGA program code. For this purpose, monitoring data is embedded into the program code and secretly stored there. The tradi-tional approach to steganographic embedding in FPGA program code is based on the use of equivalent transformations of the program code. Such transformations do not change the target function of the program code or the operation of the FPGA chip. However, the traditional approach provides a relatively small effective volume of the stego container. This leads to the fact that it is usually possible to steganographically store only control data for one type of monitoring. It is proposed to additionally use a non-equivalent approach to steganographic embedding of data into the FPGA program code. Such transformations, despite their non-equivalence, do not change the target function of the program code. This is achieved by applying transformations to the program code of units that perform arithmetic operations on approximate data. For arithmetic operations on approximate data there is often a requirement that the operands and the result are the same size. To satisfy this requirement the complete result of the operation is computed first. After that some bits of the result are discarded and rounding is performed. It is proposed to allocate elementary LUT units in the FPGA structure, which participate only in the calculation of discarded bits (and do not participate in the calculation of the remaining bits). Program codes of such LUTs can be non-equivalently changed during steganographic embedding. Distortion of the FPGA program code of such units does not distort the behavior of the FPGA chip. This is a consequence of the fact that such LUTs are not involved in the formation of the discarded bits. Results. We have developed software that, together with Intel Quartus CAD system, extracts detailed information about an FPGA project. This information includes the structure of the circuit in the project and the program codes of the units of this circuit. An application has also been developed that uses this information to determine non-equivalent steganographic resources. With the help of the devel-oped software, an experimental estimation of the additional volume of the stego container is performed. Originality. An approach to the use of non-equivalent transformations of the program code of FPGA chips for steganographic embed-ding of additional data is proposed. This approach is proposed to be used together with the traditional approach, which is based on equivalent transformations of the program code. Practical value. The steganographic embedding approach proposed in this paper allows increasing the effective volume of the stego container in the FPGA program code. By ap-plying this approach, it becomes possible to secretly store monitoring data of several types of monitoring in FPGA stego containers. References 10, figures 2.