Information_Security/RSA_.cpp at main · prityd825/Information_Security · GitHub

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
#include<bits/stdc++.h>
using namespace std;

long int p, q, n, t, flag, e[100], d[100], temp[100], j, m[100], en[100], i;
string msg;

int prime(long int);
void ce();
long int cd(long int);

void encrypt();
void decrypt();

int prime(long int pr)
{
    int i;
    j = sqrt(pr);
    for (i = 2; i <= j; i++)
    {
        if (pr % i == 0)
            return 0;
    }
    return 1;
}
     int main()
       {
        cout << "Enter the two prime number p and q: "<<endl;
        cin >> p;
        flag = prime(p);

          if (flag == 0)
    {
        cout << "\nworng input\n";
        exit(1);
    }
    cin >> q;
    flag = prime(q);
    if (flag == 0 || p == q)
    {
        cout <<endl<< "worng input"<<endl;
        exit(1);
    }
        cout <<endl<< "Enter the plaintext : "<<endl;
        fflush(stdin);
        getline(cin, msg);
        for (i = 0; msg[i] != '\0'; i++)
        m[i] = msg[i];
            n = p * q;
             t = (p - 1) * (q - 1);
                ce();
        cout <<endl<< "possible values of e and d :"<<endl;
       for (i = 0; i < j - 1; i++)
        cout << e[i] << "\t" << d[i] << "\n";
        encrypt();
        decrypt();
      return 0;
}

void ce()
{
    int k;
    k = 0;
    for (i = 2; i < t; i++)
    {
        if (t % i == 0)
            continue;
        flag = prime(i);
        if (flag == 1 && i != p && i != q)
        {
            e[k] = i;
            flag = cd(e[k]);
            if (flag > 0)
            {
                d[k] = flag;
                k++;
            }
            if (k == 99)
                break;
        }
    }
}
long int cd(long int x)
{
    long int k = 1;
    while (1)
    {
        k = k + t;
        if (k % x == 0)
            return (k / x);
    }
}
void encrypt()
{
    long int pt, ct, key = e[0], k, len;
    i = 0;
    len = msg.length();
    while (i != len)
    {
        pt = m[i];
        pt = pt - 96;
        k = 1;
        for (j = 0; j < key; j++)
        {
            k = k * pt;
            k = k % n;
        }
        temp[i] = k;
        ct = k + 96;
        en[i] = ct;
        i++;
    }
    en[i] = -1;
    cout <<endl<< "The encrypted message is: ";
    for (i = 0; en[i] != -1; i++)
        printf("%c", en[i]);
        cout<<endl;
}


void decrypt()
{
    long int pt, ct, key = d[0], k;
    i = 0;
    while (en[i] != -1)
    {
        ct = temp[i];
        k = 1;
        for (j = 0; j < key; j++)
        {
            k = k * ct;
            k = k % n;
        }
        pt = k + 96;
        m[i] = pt;
        i++;
    }
    cout<<endl;

    m[i] = -1;
    cout<<endl<<"The decrypted message is : ";
    for (i = 0; m[i] != -1; i++)
        printf("%c", m[i]);
        cout<<endl;


}