Using 'RSA' algorithm, if 𝑝 = 13,π‘ž = 5 and 𝑒 = 7. the value of 𝑑 and…

2022

UsingΒ 'RSA'Β algorithm, if 𝑝 = 13,π‘ž = 5Β and 𝑒 = 7. the value of 𝑑 and cipher value ofΒ β€²6β€²Β withΒ (𝑒,𝑛)Β key are

  1. A.

    7,4

  2. B.

    7,1

  3. C.

    7,46

  4. D.

    55,1

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Correct answer: C

Step 1: Compute n and phi(n).

n = p * q = 13 * 5 = 65. phi(n) = (p-1)*(q-1) = 12 * 4 = 48.

Step 2: Find d such that d * e ≑ 1 (mod 48).

We need the modular inverse of e = 7 modulo 48. Since 7 * 7 = 49 ≑ 1 (mod 48), we have d = 7.

Step 3: Encrypt m = 6 using the public key (e, n) = (7, 65).

Compute powers of 6 modulo 65 to get 6^7 mod 65:

  • 6^2 = 36

  • 6^3 = 6^2 * 6 ≑ 36 * 6 = 216 ≑ 21 (mod 65)

  • 6^4 ≑ 21 * 6 = 126 ≑ 61 (mod 65)

  • 6^5 ≑ 61 * 6 = 366 ≑ 41 (mod 65)

  • 6^6 ≑ 41 * 6 = 246 ≑ 51 (mod 65)

  • 6^7 ≑ 51 * 6 = 306 ≑ 46 (mod 65)

Therefore d = 7 and the ciphertext for message 6 is 46. Final answer: d = 7, ciphertext = 46.

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