Question

Q1: The figure bellow present the two-key method in 3DES.
Indicate in detail what would the result be if :

1. ?=? 13

2. ?=? 12

Q2: Alice is sending message “HIDE” to Bob. Perform encryption
and decryption using RSA algorithm, with the following
information:

Parameters p q e

11 5 7

Present all the information that you will need to encrypt and
decrypt only the first letter from tex ?

Answer #1

2.

message ="HIDE"

p = 11

q = 5

e = 7

Now, n = p q =11 5 = 55

Ø(n)= (p-1) (q-1) = (11-1) (5-1) =10 * 4 = 40 (1 < e=7 < 40 and g.c.d(40,7)=1)

Now,

e * d mod Ø(n) = 1 so, find d

7 * d mod 40 = 1

so, d=23 (7 * 23 mod 40 = 161 mod 40 = 1)

Public key : {e,n} = {7, 55}

private key : {d ,n} ={ 23, 55}

Now , for message "HIDE" we encrypt and decrypt only "H"(first letter) .And assume value of "H" is M=8.

Now,

Encryption :- C = Me mod n

so,

C = (8)7 mod 55 = 2

Decryption :- M = Cd mod n

so,

M = (2)23 mod 55 = 8 . ("H"=8).

In this way , bob get message "HIDE" form alice using RSA algorithm.Type a message

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