Home » Encryption » Crypt_Blowfish » Bug #4747

[2005-07-05 09:55 UTC] capitaine at coolsmile dot net

Description:
------------
When the length of a plain string is not a multiple of 8, decrypt() return a result with a NUL chars block appened to the end (which length is a multiple of 8).

Reproduce code:
---------------
<?
include 'Blowfish.php';
$BF = new Crypt_Blowfish('test');

while (strlen($str) < 64)
{
$str .= 'u';
test($str);
}

function test($plain)
{
global $BF;

echo "Plain string='$plain'" . " Length=" . strlen($plain) . "\n";
$ciph = bin2hex($BF->encrypt($plain));
$unciph = $BF->decrypt(pack("H" . strlen($ciph), $ciph));
echo "Unciphered string='$unciph'" . " Length=" . strlen($unciph) . "\n";
}
?>

Expected result:
----------------
No NULs appened to decrypted string.

Actual result:
--------------
Plain string='u' Length=1
Unciphered string='u' Length=8
Plain string='uu' Length=2
Unciphered string='uu' Length=8
Plain string='uuu' Length=3
Unciphered string='uuu' Length=8
Plain string='uuuu' Length=4
Unciphered string='uuuu' Length=8
Plain string='uuuuu' Length=5
Unciphered string='uuuuu' Length=8
Plain string='uuuuuu' Length=6
Unciphered string='uuuuuu' Length=8
Plain string='uuuuuuu' Length=7
Unciphered string='uuuuuuu' Length=8
Plain string='uuuuuuuu' Length=8
Unciphered string='uuuuuuuu' Length=8
Plain string='uuuuuuuuu' Length=9
Unciphered string='uuuuuuuuu' Length=16
Plain string='uuuuuuuuuu' Length=10
Unciphered string='uuuuuuuuuu' Length=16
...

[2005-07-19 11:20 UTC] capitaine at coolsmile dot net

Hi mfonda,

I didn't have a clue about cipher padding.
For whoever wants it, there is a simple workaround with the trim() function.

$plain = trim($BF->decrypt($ciph));

Thank a lot.