What will be the ciphertext produced by the following cipher function for the…

2013

What will be the ciphertext produced by the following cipher function for the plain text ISRO with key k =7. [Consider 'A' = 0, 'B' = 1, .......'Z' = 25]. Ck(M) = (kM + 13) mod 26

  1. A.

    RJCH

  2. B.

    QIBG

  3. C.

    GQPM

  4. D.

    XPIN

Attempted by 107 students.

Show answer & explanation

Correct answer: A

First, convert plaintext letters to numbers (A=0...Z=25): I=8, S=18, R=17, O=14. Apply Ck(M) = (7M + 13) mod 26. I: (56+13)%26 = 17 (R). S: (126+13)%26 = 9 (J). R: (119+13)%26 = 2 (C). O: (98+13)%26 = 7 (H). The ciphertext is RJCH.

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