The stream encipherment of ASCII character plaintext is performed in three steps:

*Step 1:* Each letter of the character plaintext *x*_{0}, *x*_{1}, …, *x*_{n−1} is replaced by its ordinal value of *x _{i}* in the ASCII character set, which is coded into 7 bits; for example

The ASCII character plaintext *x*_{0}, *x*_{1}, …, *x*_{n−1} of *n* characters is transformed into a sequence of *n* 7-bit vectors, the (0, 1)-plaintext

*Step 2:* The LFSR with initial state *s*(0) = (*s*_{0}(0), *s*_{0}(1), …, *s*_{0}(*N* − 1)) generates the key stream, a sequence of 7*n*-bits (*s*_{0}(0), *s*_{0}(l), …, *s*_{0}(7*n* − 1)), which are grouped into *n* 7-bit blocks:

*Step 3:* The ciphertext *y* = (*y*_{0}, *y*_{1}, …, *y*_{n−1}) consists of *n* 7-bit vectors where *y _{i}* is the XOR of the

The key of an LFSR encipherment system has three components:

- The number of stages
*N*of the LFSR, - The characteristic polynomial
*p*(*z*) =*c*+_{N}*c*_{N−1}*z*+ ··· +*c*_{1}*z*^{N−1}+*c*_{0}*z*^{N}, and - The initial state
*s*(0) = (*s*_{0}(0),*s*_{0}(1), …,*s*_{0}(*N*−1)).

We formulate the cribbing of ASCII character plaintext as:

Given: |
A plaintext crib ... |

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