Answer:
Explanation:
#include <iostream>
#include <string>
#include<vector>
using namespace std;
vector<int> permute(vector<int>, vector<int>);
string encrypt(vector<int>s1 , vector<int> t1, string p);
string decrypt(vector<int>s1, vector<int> t1, string p);
int main() {
string plaintext = "cryptology";
string plaintext2 = "RC4";
vector<int> S(256);
vector<int> T(256);
int key[] = { 1,2,3,6 };
int key2[] = { 5,7,8,9 };
int tmp = 0;
for (int i = 0; i < 256;i++) {
S[i] = i;
T[i] = key[( i % (sizeof(key)/sizeof(*key)) )];
}
S = permute(S, T);
for (int i = 0; i < 256 ;i++) {
cout << S[i] << " ";
if ((i + 1) % 16 == 0)
cout << endl;
}
cout << endl;
string p = encrypt(S, T, plaintext);
cout << "Message: " << plaintext << endl;
cout << "Encrypted Message: " << " " << p << endl;
cout << "Decrypted Message: " << decrypt(S, T, p) << endl << endl;
tmp = 0;
for (int i = 0; i < 256;i++) {
S[i] = i;
T[i] = key2[(i % (sizeof(key) / sizeof(*key)))];
}
S = permute(S, T);
for (int i = 0; i < 256;i++) {
cout << S[i] << " ";
if ((i + 1) % 16 == 0)
cout << endl;
}
cout << endl;
p = encrypt(S, T, plaintext2);
cout << "Message: " << plaintext2 << endl;
cout << "Encrypted Msg: " << p << endl;
cout << "Decrypted Msg: "<<decrypt(S, T, p) << endl << endl;
return 0;
}
string decrypt(vector<int>s1, vector<int> t1, string p) {
int i = 0;
int j = 0;
int tmp = 0;
int k = 0;
int b;
int c;
int * plain = new int[p.length()];
string plainT;
for (int r = 0; r < p.length(); r++) {
i = (i + 1) % 256;
j = (j + s1[i]) % 256;
b = s1[i];
s1[i] = s1[j];
s1[j] = b;
tmp = (s1[i] + s1[j]) % 256;
k = s1[tmp];
c = ((int)p[r] ^ k);
plain[r] = c;
plainT += (char)plain[r];
}
return plainT;
}
string encrypt(vector<int>s1, vector<int> t1, string p) {
int i = 0;
int j = 0;
int tmp = 0;
int k = 0;
int b;
int c;
int * cipher = new int [p.length()];
string cipherT;
cout << "Keys Generated for plaintext: ";
for (int r = 0; r < p.length(); r++) {
i = (i + 1) % 256;
j = (j + s1[i]) % 256;
b = s1[i];
s1[i] = s1[j];
s1[j] = b;
tmp = (s1[i] + s1[j]) % 256;
k = s1[tmp];
cout << k << " ";
c = ((int)p[r] ^ k);
cipher[r] = c;
cipherT += (char)cipher[r];
}
cout << endl;
return cipherT;
}
vector<int> permute(vector<int> s1, vector<int> t1) {
int j = 0;
int tmp;
for (int i = 0; i< 256; i++) {
j = (j + s1[i] + t1[i]) % 256;
tmp = s1[i];
s1[i] = s1[j];
s1[j] = tmp;
}
return s1;
}
