shift and affine cipher program in Java ND c
Affine Cipher problem :
Affine cipher is a type of monoalphabetic substitution cipher,
wherein each letter in an alphabet is mapped to its numeric equivalent, encrypted using a simple mathematical function, and converted back to a letter. The formula used means that each letter encrypts to one other letter, and back again, meaning the cipher is essentially a standard substitution cipher with a rule governing which letter goes to which.
The whole process relies on working modulo m (the length of the
alphabet used).
In the affine cipher, the letters of
an alphabet of size m are first mapped to the integers in the range
0 … m-1.
The ‘key’ for the Affine cipher consists of 2 numbers, we’ll call
them a and b. The following discussion assumes the use of a 26
character alphabet (m = 26).
A should be chosen to be relatively prime to m (i.e. a should have no factors in common with m).
Instructions while running code :
Please save file name as AffineCipher.java
Compile it using command javac AffineCipher.java
After successful compilation execute it using java AffineCipher
Java Source Code :
import java.util.Scanner;
public class AffineCipher
{
public static String encryptionMessage(String Msg,int a,int b)
{
String CTxt = "";
for (int i = 0; i < Msg.length(); i++)
{
// encryption going on here
CTxt = CTxt + (char) ((((a * Msg.charAt(i)) + b) % 26) + 65);
}
return CTxt;
}
public static String decryptionMessage(String CTxt,int a,int b)
{
String Msg = "";
int a_inv = 0;
int flag = 0;
for (int i = 0; i < 26; i++)
{
flag = (a * i) % 26;
if (flag == 1)
{
a_inv = i;
System.out.println(i);
}
}
for (int i = 0; i < CTxt.length(); i++)
{
// message decryption going on here
Msg = Msg + (char) (((a_inv * ((CTxt.charAt(i) - b)) % 26)) + 65);
}
return Msg;
}
public static void main(String[] args)
{
Scanner sc = new Scanner(System.in);
int a,b;
System.out.println("Enter the message: ");
String message = sc.next();
System.out.println("Enter values of a and b :"); a=sc.nextInt(); b=sc.nextInt(); System.out.println("Message is :" + message);
System.out.println("Encrypted Message is : "
+ encryptionMessage(message,a,b));
System.out.println("Decrypted Message is: "
+ decryptionMessage(encryptionMessage(message,a,b)));
sc.close();
}
}
// end of java source code
C source code :
#include<stdio.h> #include<string.h> #include<ctype.h> #include<stdlib.h> int CalcGCD(int); void main() { int i,j,k,gcd,a,b,numstr[100],numcipher[100]; char str[100],cipher[100]; printf("Enter a string\n"); gets(str); //converting entered string to Capital letters for(i=0,j=0;i<strlen(str);i++) { if(str[i]!=' ') { str[j]=toupper(str[i]); j++; } else { str[j]=' '; j++; } } str[j]='\0'; printf("Entered string is : %s \n",str); printf("Enter a value and must be between 1 and 25 both included\n"); scanf("%d",&a); //Checking consitions if(a<1 || a>25) { printf("a should lie in between 1 and 25\nSorry Try again !\n"); exit(0); } gcd=CalcGCD(a); if(gcd!=1) { printf("gcd(a,26)=1 but \n gcd(%d,26)=%d\nSorry Try again !\n",a,gcd); exit(0); } printf("Enter b value and must be between 0 and 25 both included\n"); scanf("%d",&b); if(b<0 || b>25) { printf("b value should lie between 0 and 25\nSorry Try again !\n"); exit(0); } //Conditions Over //Program Starts //Storing string in terms of ascii and to restore spaces I used -20 for(i=0;i<strlen(str);i++) { if(str[i]!=' ') numstr[i]=str[i]-'A'; else numstr[i]=-20; } //Ciphering Process //If numcipher is more than 25 .We need to convert and ensure that lie in between 0 and 25.(indicating Alphabets) //A-0,B-1,C-2,.....Y-24,Z-25 printf("Affine Cipher text is\n"); for(i=0;i<strlen(str);i++) { if(numstr[i]!=-20) { numcipher[i]=((alpha*numstr[i])+b)%26; printf("%c",(numcipher[i]+'A')); } else { printf(" "); } } printf("\n"); } int CalcGCD(int a) { int x; int temp1=a; int temp2=26; while(temp2!=0) { x=temp2; temp2=temp1%temp2; temp1=x; } return(temp1); }
// end of cpp source code
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