decoding encrypted message 1

joebeach · Mar 20, 2000

can someone tell me how to decode an encrypted message by using exclusive OR and using the orginal encryption key?

zBuilder · Mar 21, 2000

You mean to crack a message or just encode/decode one using the exclusiveOR method?? 
 
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joebeach · Mar 22, 2000

Kim, 
just to decode a message using XOR. I don't mind to learn how to crack a message though. 
 
Joe

zBuilder · Mar 22, 2000

Below is some very simple code that shows how to do this. It would be much more secure if more than one byte was used for the "key", but I'm keeping it simple. It also has a minor bug. Can you spot it?

#include <stdio.h> 
#include <string.h> 
 
int main() 
{ 
 
int length, x; 
char OrgString[] = "Hello there!"; 
char EncryptedStr[20]; 
char DecryptedStr[20]; 
char key = 0x55; /* The encryption/decryption key */ 
 
printf( "Original string --->%s\n", OrgString ); 
 
length = strlen( OrgString ); 
/* In the loop below we encrypt the original string with the "key"*/ 
for ( x=0; x<length; x++) 
     { 
     EncryptedStr[x] = OrgString[x] ^ key; 
     } 
EncryptedStr[x] = 0; 
printf( "Encrypted string -->%s\n", EncryptedStr ); 
 
 
length = strlen( EncryptedStr ); 
/* In the loop below we decrypt the encrypted string with the "key"*/ 
for ( x=0; x<length; x++) 
     { 
     DecryptedStr[x] = EncryptedStr[x] ^ key; 
     } 
DecryptedStr[x] = 0; 
printf( "Decrypted string -->%s\n", DecryptedStr ); 
 
return 0; 
} 
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zBuilder · Mar 23, 2000

Joebeach, 
I got your e-mail. No problem. The bug in the above code is that the message would be trunciated if any character in the "OrgString" matched the "key". If you put an uppercase U in the OrgString, you'll see what happens. I've had some fun with this (Added way more security), so check out the code below: 
 
#include <stdio.h> 
#include <string.h> 
#include <stdlib.h> 
 
int main() 
{ 
 
int length, x; 
char OrgString[] = "Hello there, and how are you today?"; 
char EncryptedStr[80]; 
char DecryptedStr[80]; 
char key = 0x55; /* The encryption/decryption key */ 
 
printf( "Original string --->%s\n", OrgString ); 
 
length = strlen( OrgString ); 
/* In the loop below we encrypt the original string with the "key" seed*/ 
srand(key); 
for ( x=0; x<length; x++) 
    { 
    EncryptedStr[x] = OrgString[x] ^ rand(); 
    } 
EncryptedStr[x] = 0; 
printf( "Encrypted string -->%s\n", EncryptedStr ); 
 
/* In the loop below we decrypt the encrypted string with the "key" seed*/ 
srand(key); 
for ( x=0; x<length; x++) 
    { 
    DecryptedStr[x] = EncryptedStr[x] ^ rand(); 
    } 
DecryptedStr[x] = 0; 
printf( "Decrypted string -->%s\n", DecryptedStr ); 
 
return 0; 
} 
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decoding encrypted message 1

joebeach

Programmer

zBuilder

MIS

joebeach

Programmer

zBuilder

MIS

zBuilder

MIS

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