Simple encryption using XOR in C/C++

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Simple encryption using XOR in C/C++

Written by:	dimport
Published by:	Nightscript
Published on:	2003-06-21 07:19:46
Topic:	C

Search OSI about C.

More articles by dimport.

viewed 129465 times

Following in the footsteps of our other encryption articles in Perl, C# and Java. Here is an example of how to perform some simple encryption in C/C++ by using the XOR method, also shown is an example of extending the XOR method by using a BLOCK.

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! XOR

xor declared as a '^' in C/C++/C# and works like this:

If both on the same position is 1 set it to 0, if one is 1 return 1 else return 0.

Here is an example:

01001101 (a)

10011100 (b)

------------

11010001 (c)

The best thing with xor is that is you xor c with b you get a, so you can easy decrypt it by applying xor with the key again. Example:

10011100 (b)

11010001 (c)

------------

01001101 (a)

! BLOCK

a way to make it harder to decypher the encrypted data is to block the data and encrypt it. This is shown in the following example:

BLOCK_SIZE = 3

thi|s i|s a| te|st

k | e| y| k|e

You split the message into block of the size 3(just as an example) and encrypt that block only with that key.

an example in C/C++:

for(int i = 0, y = 0; i <= strlen(data); ) {
  for(int o = 0; o <= BLOCK_SIZE; o++) {
    if(data[i] != '') {
      data[i] ^= key[y]; }
    i++; }
  y++;
  if(key[y] == '') {
    y = 0; }
}

This article was originally written by shab

Did you like this article? There are hundreds more.

Comments:

loureiro97
2004-12-30 21:41:20

How did this simple article get 8626 views.
Not that it's bad or anything, just that there are better articles... :?

lonetech
2005-05-04 23:25:08

Simple - you have to view it to tell what it contains. In this case, not terribly much. I don't see the point of skipping spaces in the algorithm; you're likely to run into a fencepost error anyway, the moment someone uses the same character as key and data.

BhanuTeja
2005-05-25 16:15:18

Anyone can easily break this type of crypto-system.

Anonymous
2006-01-23 19:44:28

I think that's why its called a "Simple" encryption system. It is used to illustrate that crypto-systems need bijective functions (its inverse is also a function). This is important because once you apply the function you need to be able to take the encrypted value back.

-Al

anilg
2006-01-24 08:08:25

Yeah.. this is sort of a very young brother of OTP.. which is the only proven 100% secure cryptosystem

Anonymous
2006-01-24 22:47:06

otp unless implemented incorrectly is 100% secure

aidan
2006-01-25 09:27:36

There are inherent problems with the initial key distribution, and of course you also have to keep the pad secure. But it can be implemented correctly.

anilg
2006-01-26 05:41:16

The drawback is he key is as long as the message itself. So you'll have to first send across the "pad" to the recipent.

The +ve is that since the key is as long as the message itself.. the ciphertext, for ex:

a shd ajsdh jahdjakshdasjdh

could decrypt to:

"Hey we need more artillary"

or

"Whoa! send some girls over"

Anonymous
2006-04-16 11:52:15

xor in vc

xpi0t0s
2006-04-19 11:02:29

um, what about it? ^ as the xor operator works fine in Visual C++; I've used it myself on numerous occasions.

Anonymous
2006-07-18 19:51:15

I wrote a commandline based XOR encryption program that takes in as the argument the key.
The program works fine, however if there are too many characters in the file to be deciphered, the program will not properly decipher the file, instead I get half of the file deciphered, and the rest is just a bunch of useless ciphertext junk. What would cause the XOR encryption to behave like that, just because there are too many characters to decipher.

note: I wrote the program so that if the key is longer than the string to decipher, the program resets to the beginning of the key.

EX:
KEY: ABC
STRING: hello World!!!

h ^ A
e ^ B
l ^ C
l ^ A
o ^ B
' ' ^ C
etc . . .

my syntax diagram:

Usage: aenc Filename key

anilg
2006-07-19 05:10:29

The source code would help find the problem. Use the forum to post it.

Anonymous
2006-07-23 13:58:57

How can I become a member of this websites forum?

Anonymous
2006-07-23 17:45:50

go there:

http://www.osix.net/signup.php

Anonymous
2006-12-28 08:19:43

BTW, it's 100% secure only in a case when length of key is equal to message length. It seems to be so...

Anonymous
2007-01-10 19:33:11

Let me answer why this article is so popular, there is a site called http://www.ouverture-facile.com/ full of riddles to solve, a there is one that uses XOR encryption, it was recently digged, so many people are finding this article in the first page when they google XOR encryption

Anonymous
2007-01-18 03:38:10

encryption and decryption in c++

Anonymous
2007-03-08 09:37:30

A very simple encryption method, easily bypassed, and yet it does provide beginners a simple example of how it's done.

Anonymous
2007-03-25 19:02:19

why be so negative? this guy has taken the time to post his code. newbies may find it useful.

Anonymous
2007-04-12 10:40:20

Hey I found this useful! thanks for taking the time to show us simple and easy to understand code. Programming is like lifting weights, if you don't do it a lot you can't just go and lift 300lb. This example was an awesome starter! Please do more of these in the future.

Anonymous
2007-07-04 09:48:52

If you have a totally random key the same length as the plain-text, securely distributed beforehand to the receiving party, this simple XOR scheme is perfectly secure. This is called a one-time pad. Mathematics can't break it, so the NSA couldn't break it either.

Anonymous
2007-11-23 02:12:06

Nice routines and very well written keep it up, thank you for sharing SEO Expert it's easy to follow and understandable.

Anonymous
2009-04-11 13:24:17

NEVER USE STR.LENGTH IN ANY LOOP !!!!!!!!!!!!!!!!!

Anonymous
2009-04-28 12:41:34

can a simple encryption algorithm not possible using non-linear feedback shift register concept?...cause that would increase the security to a great level, as well as would be simple also..

Anonymous
2009-05-02 00:41:13

> A very simple encryption method,
> easily bypassed

Since its so easy... explain it in a few short sentences.

Anonymous
2009-11-12 13:11:20

Nothing wrong with str.length if you've got a compiler that doesn't suck

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