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.

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. A linear feedback shift register is a register of bits that performs discrete. Correct and detailed answer will be Upvoted else downvoted.

The list of 16-bit LFSRs has 2048 entries. Find the 4-bit linear-feedback shift registers that produce the following output streams. A vector with entries would initialize the shift register. An LFSR of length m consists of m stages numbered, each capable of storing one bit, and a clock controlling data exchange. The XOR function can also be viewed as part of the digital addition function in that XORs are used as the Sum portion of the. A linear feedback shift register (LFSR) is a shift register whose input bit is the output of a linear function of two or more of its previous states (taps). A common linear function of single bits is the XOR. This page contains lists of feedback constants that work with LFSRs of different lengths. Background: In digital signal processing, a linear-feedback shift register, or LFSR, is a shift register where the input bit is a linear function of its previous state. (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). When this bit is zero, this has no effect, but when it is 1, all these bits are flipped. 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. Their series of pulls and XOR are what ultimately feed into the calculation of the final bit.The Wikipedia article you got this from has an illustration that explains what the code is doing: A linear-feedback shift register (LFSR) is a register of bits that performs. The two most important operations in the LFSR advance you posted are: /* taps: 16 14 13 11 feedback polynomial: x^16 + x^14 + x^13 + x^11 + 1 */īit = ((lfsr > 0) ^ (lfsr > 2) ^ (lfsr > 3) ^ (lfsr > 5)) & 1u That value is then placed into the most-significant bit of the register after shifting the register down one bit. With an LFSR a rolling feedback is calculated that ultimately determines a single bit value.

4 bit linear feedback shift register