Cryptography Tool (Cipher Wheel)

A cipher is a set of rules for converting between plain text and cipher-text. These rules often use a secret key.

  

A Virtual Cipher Wheel  : http://invpy.com/cipherwheel 

How to Encrypt with the Cipher Wheel

First, write out your message in English on paper. For this example we will encrypt the message, “The secret password is Rosebud.” Next, spin the inner wheel around until its letters match up with letters in the outer wheel. Notice in the outer wheel there is a dot next to the letter A. Look at the number in the inner wheel next to the dot in the outer wheel. This number is known the encryption key.

The encryption key is the secret to encrypting or decrypting the message

So the steps to encrypt a letter are:

1. Decide on a key from 1 to 25. Keep this key secret!

2. Find the plain-text letter’s number.

3. Add the key to the plain-text letter’s number.

4. If this number is larger than 26, subtract 26.

5. Find the letter for the number you’ve calculated. This is the cipher-text letter.

6. Repeat steps 2 to 5 for every letter in the plain-text message.

To decrypt, subtract the key instead of adding it. For the cipher-text letter B, the number is 1. Subtract 1 – 13 to get -12. Like our “subtract 26” rule for encrypting, when we are decrypting and the result is less than 0, we have an “add 26” rule. -12 + 26 is 14. So the cipher-text letter B decrypts back to letter O.

Code:

#include<iostream>
#include<cstring>
//#include<ctype>
char * encript(int k,char *text);
char * decript(int k,char *text);
using namespace std;

int main()
{
char text[50];
int key,x;
cout<<"Enter the text:";
cin>>text;
cout<<"Enter encryption key:";
cin>>key;
cout<<"Press 1 for Encryption\nPress 2 for Decryption\n";
cin>>x;
if(x==1)
cout<<"Encripted text:"<<encript(key,text)<<endl;
else
cout<<"Decripted text:"<<decript(key,text)<<endl;

return(0);
}


char * encript(int key,char *text)
{
int ti;
for(int i=0;i<strlen(text);i++)
{
  if(isalpha(text[i])&&(isupper(text[i])))
   {
        ti=(int)text[i];
        ti+=key;
       if(ti>90)
        ti-=26;
       text[i]=(char)ti;

   }

 if(isalpha(text[i])&&(islower(text[i])))
   {
        ti=(int)text[i];
        ti+=key;
       if(ti>122)
        ti-=26;
       text[i]=(char)ti;

   }



}
return(text);
}

char * decript(int key,char *text)
{

int ti;
for(int i=0;i<strlen(text);i++)
{
  if(isalpha(text[i])&&(isupper(text[i])))
   {
        ti=(int)text[i];
        ti-=key;
       if(ti<65)
        ti+=26;
       text[i]=(char)ti;

   }

 if(isalpha(text[i])&&(islower(text[i])))
   {
        ti=(int)text[i];
        ti-=key;
       if(ti<97)
        ti+=26;
       text[i]=(char)ti;

   }



}
return(text);

}