vernam encryption

[aleicaro]

There is someone who had written the algorithm for encryption "Vernam encryption" in php?

Thank you very much.

[Natty_Dreadlock]

i think u know the algorithm, however, here's a short manual: http://world.std.com/~franl/crypto/one-time-pad.html .
It should be quite easy to rewrite the algorithm in php, i think i could do it, probably there are already implementations...
Here the basic steps:
Generate random key (mt_rand())
Go through the string to decrypt and xor one character with the corresponding key char.
Here's a tutorial how to do it in asp http://www.4guysfromrolla.com/webtech/110599-1.2.shtml , i guess u can use this as a starting point if u wanna code the algortihm in php.
hth and feel free to ask further questions

[aleicaro]

I've already translated the code written with vbscript in php, but this don't work properly, and the result of the decryption is a wrong string. I will want to see the algorithm written in php to compare the code...

[Natty_Dreadlock]

so plz post your encryption code and i'll check if i find some error. btw, why do u want to use one-time-pad encryption?? u know it only works for keys that are exactly as long as your input data? U can also have a look at www.php.net/mcrypt , it allows u to use lots of block and stream ciphers - maybe they r not as secure as one-time-pad aka Vernam encryption but they r far more easy to handle...

[shawon22]

i don't know if i did it right so guys plz correct me if i'm wrong

here is the code:

$str = 'this is string';


echo "<b>Original Text:</b> $str<br>";


$key = Array();
for($i=0; $i<512; $i++)
$key[$i] = rand()*$i;


$c = Array();
echo "<b>Encrypted String: </b>: ";
for($i=0; $i<strlen($str); $i++)
{
	$c[$i] = $key[$x] ^ ord($str[$i]);

$x = $x+1;
if($x>512)
	$x=0;
echo chr($c[$i]);
}

echo "<p>";

//decrypt

for($i=0; $i<count($c); $i++)
	echo chr($key[$i]^$c[$i]);

[Natty_Dreadlock]

most of your code is ok, however i think u reuse the key bits every 512 chars... i think an attacker could exploit this. maybe u should better create a keystream which is as long as the data u wanna encrypt. u just need to modify your for loop a little ($i < strlen($str) ) and remove the $x in the encryption loop, just use $i for all strings.
Moreover, u gotta seed the random number generator usin srand(time()), and use the mt_rand function (www.php.net/mt_rand) which will give u better random values (here u have to use mt_srand to initialize).
hth

[drawmack]

give me a couple hours I'll throw one together, just have to translate my c++ code to php.

[drawmack]

and here it is