Here's some example code that will do the job. To obfuscate a series of byte values, you might find it easier to extract just 8 bits at each iteration. LFSR is a Linear Feedback Shift Register which is used to create random numbers but to a limit where it depends on the no of used bits then a sequence of numbers will begin it xors N-1 input together and the output is tied to the input then the input is shifted each time a new output is generated The output tied to the MSB of the input to get th. Just XOR these values with your data to obfuscate it, and repeat the process using the same sequence of numbers to retrieve the original data. Obfuscating data with an LFSR:Īs long as your LSFR initially contains a non-zero value, it will step through a sequence of 65535 (2 16–1) pseudorandom values at every iteration.
The list of 16-bit LFSRs has 2048 entries. This page contains lists of feedback constants that work with LFSRs of different lengths. (Note: There is no XOR gate feeding into bit 16 because there is no input from bit 17.) Other LFSRs: The quickest way of doing this is by calculating the XOR product of the 16-bit shift register with 0xB400, which has all of these bits set (1011010000000000 in binary). It took me some effort to understand, the final help was this really good page, much better than the (at first) cryptic wikipedia entry. When this bit is zero, this has no effect, but when it is 1, all these bits are flipped. 11 Lately I bumped repeatedly into the concept of LFSR, that I find quite interesting because of its links with different fields and also fascinating in itself. The least significant bit extracted from the end of the shift register is fed back by XOR-ing it with bits 16, 14, 13 and 11. The Wikipedia article you got this from has an illustration that explains what the code is doing:
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