Consider an affine cipher whose key parameters are defined as follows

Question:

Consider an affine cipher whose key parameters are defined as follows: a = 7 and b = 22.

  1. Decrypt the following text: falszztysyjzyjkywjrztyjztyynaryjkyswarztyegyyj
  2. Who wrote the line?

Answer:

We first need identify these letters with integer values .
a=0, b=1…z=25
These values are then used as inputs to a function of the following form .
f(x)=ax+b mod(26)
where a=7 and b=22 has been given

affine coefficient by modular inverse

a=7
a’=15
b=22
b’=22

therefore the encypted texts:

falszztysyjzyjkywjrztyjztyynaryjkyswarztyegyyj

decrypted text would be
FIRSTTHESENTENCEANDTHENTHEEVIDENCESAIDTHEQUEEN (firstthesentenceandthentheevidencesaidthequeen)

therefore the message is = “first the sentence and then the evidence said by queen”
therefore the Answer of the question number 2 is “queen” said this.

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