Question

In: Advanced Math

In practice, an LFSR sequence would not be used as keystream for a stream cipher, due...

In practice, an LFSR sequence would not be used as keystream for a stream cipher, due to the linear complexity. Answer the following questions about linear complexity.

What is the linear complexity of a maximal length LFSR output sequence?
Describe one method using LFSRs to produce a binary output sequence but with increased linear complexity. Draw a diagram to illustrate your construction.

Expert Solution

a.

Linear complexity is also called linear span.If an LFSR sequence of n stages has the maximal period ,then it is called a maximal length sequence,shortened as m - sequence.

b.

One standed wa is as follows.Let, n primitive LFSR with lengths with ,

now we take the GCD

and take a nonlinear boolean function

with

for that we have a output of linear complexity

evaluted over the integers, where output of LFSR is input as the variable of the bolean function.this is called the combination generator,

example.

Colby Messinger answered 2 years ago

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