crypt() returning duplicate values?

Anon

I need to be able to take unique 12 character strings and turn each into a new, unique 12 character string.

I tried using crypt($string,$seed) with a fixed two character seed (not using this for security, but for simple obfuscation).

The problem is that crypt() is generating duplicate strings from different, unique input strings.

For instance, crypt on "436643314143", "436643314147" and "436643314148" produces identical results.

Any suggestions?

Thx,
Kurt

andreas

try md5()...

it might work better for you...

Andreas

Anon

MD5() would be fine except that this is an application that is currently up and running for a major corporation and the database field length is already set to 12 characters.

As I understand it, MD5() returns a longer string and I can really only modify the database as a last resort.

I need something that takes the 12 character string and returns an encrypted 12 character string.

Any other ideas?

kparker

Sure, it's theoretically possible. Can't you just detect it when it happens and alter the salt until the result is unique?

inter_joe

maybe rot-13 can help you. it is sometimes used to "crypt" emails. every char will be shifted 13 places up. 13 because the "normal" alphabet has 26 chars. so when you shift twice, you are at the start again.

see the following functions for some examples:
rot_13() will do the "normal" shift with strings.
rot_13x() integrates numbers (which will be shifted by 5)
rot_18() will put the numbers "into" the alphabet

function rot_13($string)
{
$from = "abcdefghijklmnopqrstuvwxyz";
$to = "nopqrstuvwxyzabcdefghijklm";
return strtr($string, $from, $to);
}
function rot_13x($string)
{
$from = "abcdefghijklmnopqrstuvwxyz0123456789";
$to = "nopqrstuvwxyzabcdefghijklm5678901234";
return strtr($string, $from, $to);
}

function rot_18($string)
{
$from = "abcdefghijklmnopqrstuvwxyz0123456789";
$to = "stuvwxyz0123456789abcdefghijklmnopqr";
return strtr($string, $from, $to);
}

$s = "cryptme12345";

echo "original:$s ";
echo "rot-13:".rot_13($s)." ";
echo "rot-13x:".rot_13x($s)." ";
echo "rot-18:".rot_18($s)." ";

$s = rot_13(rot_13x(rot_18($s)));
echo "all-together:$s ";

$s = rot_18(rot_13x(rot_13($s)));
echo "original:$s ";

will output:

original:cryptme12345
rot-13:pelcgzr12345
rot-13x:pelcgzr67890
rot-18:u9g7b4wjklmn
all-together:u4g2b9wjklmn
original:cryptme12345

hope that helps. may write your own shift-funcs. strtr() is very handy for that.
these are no crypt funcs, of course.
things like:
echo rot_13("hellohello") -> uryyburyyb are quite obvious.
you can work with strrev(), or, if you'll always have a fixed-size string,
split him up in smaller parts and change their order.
many things you can do.

have fun
joe

Anon

If you are using a loop to create the new strings you could change the seed each time by making it an array... $seed[$i]

I'm having problems using the crypt() method to generate an .htpasswd file. I used to be able to use this method fine running on Linux Red Hat, but now that we've changed to freeBSD it won't authenticate the password...Any ideas?

Anon

I fixed the problem using crypt() for .htpasswd files on freeBSD by adding my own salt, instead of letting PHP generate it for me.