Thread: XOR encryption

Originally Posted by dwks

It's quite simple.
Use the code in the first loop in the second one.

Code:

/* decrypt loop */
      for ( i = 0; encry[i] != '\0'; i++ ) 
      {
          plain[i] = encry[i] ^ key[keypos];
          keypos++;
                if ( keypos > keylen )
                   keypos = 0;
          
      }

Well, that's actually the first thing I tried, but I get garbage for output. I thought it would be the logical choice.. Here's the code, and whenever I try to decrypt I get garbage.. There has to be something wrong with the loops.. Saturday evening and I'm trying to get a XOR program to work.. Well, at least I'm committed :-)

Code:

#include <stdio.h>
#include <string.h>
main()
{
      char        plain[51];
      char        encry[51];
      char        key[5] = "ABCD";
      int         i, keylen = 0, keypos = 0;
      
      printf("Enter text: ");
      scanf("%[^\n]", plain);
      printf("You entered: %s\n", plain);
      keylen = strlen(key);
      printf("Encryption key is: %s\n", key);
      printf("Length of key is: %d\n", keylen);
      
      for ( i = 0; plain[i] != '\0'; i++ ) 
      {
          encry[i] = plain[i] ^ key[keypos];
          keypos++;
                if ( keypos > keylen )
                   keypos = 0;
                         
      }                 
      puts("Encrypted text: ");
      puts(encry);   
                        
      for ( i = 0; encry[i] != '\0'; i++ ) {
          plain[i] = encry[i] ^ key[keypos];
          keypos++;
                if ( keypos > keylen )
                   keypos = 0;
          }
          
      puts("Decrypted: ");
      puts(plain);
      
      fflush(stdin);
      getchar();
}