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//railfence
#include<stdio.h>
#include<string.h>
#include<stdlib.h>
char *plainTextToCipherText(char plainText[],int n)
{
int i,j,counter,limit,index=0,len;
char *cipherText;
len=strlen(plainText);
cipherText=(char*)malloc(sizeof(char)*(len+1));
for(i=0;i<n;i++)
{
counter=0;
for(j=i;j<len;j+=limit)
{
cipherText[index++]=plainText[j];
if(i==0 || i==n-1)
limit=2*n-2;
else if(counter%2==0)
limit=2*(n-i-1);
else
limit=2*i;
if(limit<=0)
break;
counter++;
}
}
cipherText[index]='\0';
return cipherText;
}
int main()
{
int n;
char plainText[100];
printf("Enter the plain text : ");
scanf("%s",plainText);
printf("Enter the value of n (key) : ");
scanf("%d",&n);
printf("%s\n",plainTextToCipherText(plainText,n));
return 0;
}
/*
#include<stdio.h>
#include<string.h>
void main()
{
int i,j,k,l;
char a[20],c[20],d[20];
printf("\n\t\t RAIL FENCE TECHNIQUE");
printf("\n\nEnter the input string : ");
gets(a);
l=strlen(a);
/*Ciphering*/
for(i=0,j=0;i<l;i++)
{
if(i%2==0)
c[j++]=a[i];
}
for(i=0;i<l;i++)
{
if(i%2==1)
c[j++]=a[i];
}
c[j]='\0';
printf("\nCipher text after applying rail fence :");
printf("\n%s",c);
/*Deciphering*/
if(l%2==0)
k=l/2;
else
k=(l/2)+1;
for(i=0,j=0;i<k;i++)
{
d[j]=c[i];
j=j+2;
}
for(i=k,j=1;i<l;i++)
{
d[j]=c[i];
j=j+2;
}
d[l]='\0';
printf("\nText after decryption : ");
printf("%s",d);
}
*/
-------------------------------------------------------------------------------------------------------------------
//vignere
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>
char* encrypt(char* message, char* key);
char* decrypt(char* message, char* key);
int main()
{
char message[1000], key[1000], *encrypted, *decrypted;
int choice;
printf("Enter message: ");
fgets(message, 1000, stdin);
printf("Enter key: ");
fgets(key, 1000, stdin);
// remove newline characters from input
message[strcspn(message, "\n")] = '\0';
key[strcspn(key, "\n")] = '\0';
printf("Enter your choice:\n");
printf("1. Encrypt\n");
printf("2. Decrypt\n");
scanf("%d", &choice);
switch (choice) {
case 1:
encrypted = encrypt(message, key);
printf("Encrypted message: %s\n", encrypted);
free(encrypted);
break;
case 2:
decrypted = decrypt(message, key);
printf("Decrypted message: %s\n", decrypted);
free(decrypted);
break;
default:
printf("Invalid choice!\n");
break;
}
return 0;
}
char* encrypt(char* message, char* key)
{
char* encrypted = (char*)malloc(strlen(message) + 1);
int messageLength = strlen(message), keyLength = strlen(key), i, j;
for (i = 0, j = 0; i < messageLength; ++i, ++j) {
if (j == keyLength)
j = 0;
// add key value to message character
encrypted[i] = ((toupper(message[i]) - 'A' + toupper(key[j]) - 'A') % 26) + 'A';
}
encrypted[i] = '\0';
return encrypted;
}
char* decrypt(char* message, char* key)
{
char* decrypted = (char*)malloc(strlen(message) + 1);
int messageLength = strlen(message), keyLength = strlen(key), i, j;
for (i = 0, j = 0; i < messageLength; ++i, ++j) {
if (j == keyLength)
j = 0;
// subtract key value from message character
decrypted[i] = ((toupper(message[i]) - 'A' - (toupper(key[j]) - 'A') + 26) % 26) + 'A';
}
decrypted[i] = '\0';
return decrypted;
}
-------------------------------------------------------------------------------------------------------------------------
//diffie
#include<stdio.h>
#include<conio.h>
#include<math.h>
// global parameter
int p = 11, g = 2;
int a, b;
int main()
{
int x, y, ssk1, ssk2;
printf("Alice Choice: ");
scanf("%d", &x);
printf("Bob Choice: ");
scanf("%d", &y);
// Alice
a = (long int) pow(g, x) % p;
// Bob
b = (long int) pow(g, y) % p;
// SSK for ALICE
ssk1 = (long int) pow(b, x) % p;
// SSK for BOB
ssk2 = (long int) pow(a, y) % p;
printf("SSK1 = %d and SSK2 = %d", ssk1, ssk2);
getch();
return 0;
}
-------------------------------------------------------------------------------------------------------------
//RSA
#include<stdio.h>
#include<conio.h>
#include<math.h>
// 1. select p and q
// 2. n = p*q
// 3. phi = (p-1)*(q-1)
// 4. choose public key e such that 1<e<phi, gcd(e, phi)=1
// 5. calculate privat key: e*d = 1 mod phi
// 6. Encryption: c = m^e mod n -- m message, c cipher
// 7. Decryption: m = c^d mod n
long long int p = 7, q = 11;
long long int gcd(long long int, long long int);
//long int mypow(long int, long int);
int main()
{
long long int n, phi, e, d;
long long int m = 2, c;
//2
n = p*q; // 77
//3 Euler toitent function
phi = (p-1)*(q-1); // 60
//4. choose public key
p:
printf("Enter public component: ");
scanf("%lld", &e); // 13
// range 1<e<phi, gcd(e,phi)==1
// printf("GCD = %ld", gcd(phi, e));
// printf("GCD = %ld\n", gcd(phi, e));
if(!(e>1 && e<phi && gcd(phi,e)==1))
{
printf("Public component is not selected properly.\n");
goto p;
}
//printf("Okay!");
// 5 find private key e * d = 1 mod phi
// Simple searching strategy
// In real implementation use proper algorithm.
d = 2;
while(e*d % phi != 1)
{
// printf("checking = %ld\n", d);
d++;
}
printf("\nPrivate Key = %ld\n", d);
// 6. Encryption
//printf("\nm^e = %lld\n", (long long int) pow(m, e));
c = (long long int) pow(m, e) % n;
printf("\nCipher: %lld\n", c);
// 7. Decryption
//printf("\nc^d = %lld\n", (long int)pow(c,d));
m = (long long int) pow(c, d) % n;
printf("\nPlain: %lld\n", m);
getch();
return 0;
}
long long int gcd(long long int a, long long int b)
{
long long int q, r, tmp;
/* use if required
if (b>a)
{
tmp = a;
a = b;
b = tmp;
}
*/
while (b!=0)
{
q = a/b;
r = a%b;
a = b;
b = r;
}
return a;
}
/*
long int mypow(long int a, long int b)
{
long int p=1, i;
for(i=1;i<b;i++)
{
p *= a;
}
return p;
}
*/
------------------------------------------------------------------------------------------------------
//caesar
#include<stdio.h>
int main()
{
char message[100], ch;
int i, key;
printf("Enter a message to encrypt: ");
gets(message);
printf("Enter key: ");
scanf("%d", &key);
for(i = 0; message[i] != '\0'; ++i){
ch = message[i];
if(ch >= 'a' && ch <= 'z'){
ch = ch + key;
if(ch > 'z'){
ch = ch - 'z' + 'a' - 1;
}
message[i] = ch;
}
else if(ch >= 'A' && ch <= 'Z'){
ch = ch + key;
if(ch > 'Z'){
ch = ch - 'Z' + 'A' - 1;
}
message[i] = ch;
}
}
printf("Encrypted message: %s\n", message);
//decrypt
for(i = 0; message[i] != '\0'; ++i){
ch = message[i];
if(ch >= 'a' && ch <= 'z'){
ch = ch - key;
if(ch < 'a'){
ch = ch + 'z' - 'a' + 1;
}
message[i] = ch;
}
else if(ch >= 'A' && ch <= 'Z'){
ch = ch - key;
if(ch < 'A'){
ch = ch + 'Z' - 'A' + 1;
}
message[i] = ch;
}
}
printf("Decrypted message: %s", message);
return 0;
}
---------------------------------------------------------------------------------------------------------------
//MONOALPHABATIC CIPHER
#include<stdio.h>
#include<conio.h>
#include<string.h>
void main()
{
char pt[26]={'A','B','C','D','E','F','G','H','I','J','K','L','M','N','O','P','Q','R','S','T','U','V','W','X','Y','Z'};
char ct[26]={'Z','Y','X','W','V','U','T','S','R','Q','P','O','N','M','L','K','J','I','H','G','F','E','D','C','B','A'};
char p[20]={'\0'},c[20]={'\0'},r[20]={'\0'};
int i,j;
printf("\n enter the plain text:");
gets(p);
//converting plain text into cipher text (encryption)
for(i=0;i<strlen(p);i++)
{
for(j=0;j<26;j++)
{
if(pt[j]==p[i])
{
c[i]=ct[j];
}
}
}
printf("\n cipher text is: %s",c);
//converting cipher text into plain text (decryption)
for(i=0;i<strlen(c);i++)
{
for(j=0;j<26;j++)
{
if(ct[j]==c[i])
{
r[i]=pt[j];
}
}
}
printf("\n \n plain text is: %s",r);
getch();
}
--------------------------------------------------------------------------------------------------------------
//euclidean
#include<stdio.h>
#include<conio.h>
int main()
{
int a, b, q, r, t;
clrscr();
printf("Enter number a: ");
scanf("%d", &a);
printf("Enter number b: ");
scanf("%d", &b);
// large case
if (b>a)
{
t = a;
a = b;
b = t;
}
printf("q\ta\tb\tr\n");
do
{
q = a/b;
r = a%b;
printf("%d\t%d\t%d\t%d\n", q, a, b, r);
a = b;
b = r;
if(b==0)
{
printf("%d\t%d\t%d\t%d\n", q, a, b, r);
}
}while(b!=0);
printf("GCD = %d", a);
getch();
return 0;
}
----------------------------------------------------------------------------------------------------------
//extended euclidean
#include<stdio.h>
#include<conio.h>
int main()
{
int a, b, q, r, temp, s1=1, s2=0, s, t1=0, t2=1, t, N;
clrscr();
printf("Enter number a: ");
scanf("%d", &a);
printf("Enter number b: ");
scanf("%d", &b);
// large case
if (b>a)
{
temp = a;
a = b;
b = temp;
}
N = a;
printf("q\ta\tb\tr\ts1\ts2\ts\tt1\tt2\tt\n");
do
{
q = a/b;
r = a%b;
s = s1 - q*s2;
t = t1 - q*t2;
printf("%d\t%d\t%d\t%d\t%d\t%d\t%d\t%d\t%d\t%d\n", q, a, b, r, s1, s2, s, t1, t2, t);
a = b;
b = r;
s1 = s2;
s2 = s;
t1 = t2;
t2 = t;
if(b==0)
{
printf("%d\t%d\t%d\t%d\t%d\t%d\t%d\t%d\t%d\t%d\n", q, a, b, r, s1, s2, s, t1, t2, t);
}
}while(b!=0);
printf("GCD = %d\n", a);
//multiplicative inverse (t1)
t1>0 ? printf("Multiplicative inverse: %d", t1): printf("Multiplicative inverse: %d", t1+N);
getch();
return 0;
}
------------------------------------------------------------------------------------------------------------
//Relatively prime
#include<stdio.h>
#include<conio.h>
int main()
{
int a, b, q, r, t;
printf("Enter number a: ");
scanf("%d", &a);
printf("Enter number b: ");
scanf("%d", &b);
// large case
if (b>a)
{
t = a;
a = b;
b = t;
}
printf("q\ta\tb\tr\n");
do
{
q = a/b;
r = a%b;
printf("%d\t%d\t%d\t%d\n", q, a, b, r);
a = b;
b = r;
if(b==0)
{
printf("%d\t%d\t%d\t%d\n", q, a, b, r);
}
}while(b!=0);
printf("GCD = %d\n", a);
if(a==1)
{
printf("Given numbers are relatively prime.");
}
else
{
printf("Given numbers are not relatively prime.");
}
getch();
return 0;
}
------------------------------------------------------------------------------------------------------------------
//primtive root
#include<stdio.h>
#include<conio.h>
#include<math.h>
int check_unique(int t[100], int n)
{
int i, j, flag = 1;
for(i=0;i<n;i++)
{
for(j=i+1; j<n; j++)
{
if(t[i] == t[j])
{
flag = 0;
break;
}
}
}
return flag;
}
int main()
{
int m, n, i, t[100];
printf("Enter number: ");
scanf("%d", &n);
printf("Enter modulo: ");
scanf("%d", &m);
// logic
for(i=1;i<m; i++)
{
t[i-1] = (long int) pow(n, i) % m;
}
// display value
for(i=0;i<m-1;i++)
{
printf("%d\t", t[i]);
}
// check
check_unique(t, m-1)==1 ? printf("\nYES"):printf("\nNO");
getch();
return 0;
}
---------------------------------------------------------------------------------------------------------
//elagamal
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
int is_prime(int num) {
int i;
for (i = 2; i <= sqrt(num); i++) {
if (num % i == 0) {
return 0;
}
}
return 1;
}
int generate_prime(int min, int max) {
int num = min + rand() % (max - min);
while (!is_prime(num)) {
num++;
}
return num;
}
int power(int a, int b, int p) {
int result = 1;
while (b > 0) {
if (b % 2 == 1) {
result = (result * a) % p;
}
a = (a * a) % p;
b /= 2;
}
return result;
}
int main() {
int p, g, x, y, k, m, r, e, d;
printf("Enter a prime number p: ");
scanf("%d", &p);
while (!is_prime(p)) {
printf("p is not prime. Enter a prime number p: ");
scanf("%d", &p);
}
printf("Enter a generator g: ");
scanf("%d", &g);
// while (g <= 1 || g >= p - 1 || power(g, (p - 1) / 2, p) != 1) {
// printf("g is not a generator. Enter a generator g: ");
// scanf("%d", &g);
// }
printf("Enter a private key x: ");
scanf("%d", &x);
printf("Enter a message m: ");
scanf("%d", &m);
y = power(g,x,p);
k = generate_prime(2, p - 2);
r = power(g, k, p);
e = (m * power(y, k, p)) % p;
d = (e * power(r, p - 1 - x, p)) % p;
printf("Public key (p, g, y) = (%d, %d, %d)\n", p, g, y);
printf("Private key x = %d\n", x);
printf("Message m = %d\n", m);
printf("Random integer k = %d\n", k);
printf("Encrypted message (r, e) = (%d, %d)\n", r, e);
printf("Decrypted message d = %d\n", d);
return 0;
}
---------------------------------------------------------------------------------------------------------------
//miller rabin
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
// function to compute (base^exponent) modulo modulo
int modularExponentiation(int base, int exponent, int modulo)
{
int result = 1;
while (exponent > 0) {
if (exponent % 2 == 1) {
result = (result * base) % modulo;
}
base = (base * base) % modulo;
exponent /= 2;
}
return result;
}
// function to test if n is prime using Miller-Rabin test with k iterations
int millerRabin(int n, int k)
{
if (n == 2 || n == 3) {
return 1;
}
if (n == 1 || n % 2 == 0) {
return 0;
}
// write n-1 as (2^r)*d where d is odd
int r = 0, d = n - 1;
while (d % 2 == 0) {
++r;
d /= 2;
}
int i, j;
for (i = 0; i < k; ++i) {
int a = rand() % (n - 3) + 2; // pick a random number in [2, n-2]
int x = modularExponentiation(a, d, n);
if (x == 1 || x == n - 1) {
continue;
}
for (j = 1; j < r; ++j) {
x = (x * x) % n;
if (x == n - 1) {
break;
}
}
if (j == r) {
return 0;
}
}
return 1;
}
int main()
{
int n, k;
printf("Enter the number to be tested: ");
scanf("%d", &n);
printf("Enter the number of iterations: ");
scanf("%d", &k);
srand(time(NULL)); // seed the random number generator with the current time
if (millerRabin(n, k)) {
printf("%d is probably prime.\n", n);
} else {
printf("%d is composite.\n", n);
}
return 0;
}
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