RE: [PHP] running str_replace, it misbehaves!

[Ford, Mike]

> -Original Message-
> From: Allen McCabe [mailto:allenmcc...@gmail.com]
> Sent: 16 August 2009 22:07

[...]
 
> Here is an example of my code:
> 
> [code]
> 
>  //ENCRYPT FUNCTIONS
> function format_string($string,$functions)
> { $funcs = explode(",",$functions);
> foreach ($funcs as $func)
> {
> if (function_exists($func)) $string = $func($string);
> }
> return $string;
> }
> function enc_string($string)
> {  $search =
> array("a","b","c","d","e","f","g","h","i",".."); //62
> values
>  $replace = array("j9","k8","q7","v6","..."); //62 values
>  $string = str_replace($search, $replace, $string);
>  $search2 =
> array("9k","8q","7v","6w","5x","4y","3z","2j","");
> // 126
> values
>  $string = str_replace($search2, $replace2, $string);
>  return $string;
> }

When you feed array search and replace values to str_replace, it runs them in 
sequence, not in parallel

As you haven't given us a full input alphabet above (and, incidentally, you've 
left out the value of $replace2!), I can't give an example using your encoding, 
so let's just take, for example:
 
$string = 'word';

and feed it through

str_replace(array('d','o','r','w'), array('w9', 'r8', 'o7', 'd6'), $string);

This proceeds as follows:

d -> w9 = worw9
o -> r8 = wr8rw9
r -> o7 = wo78o7w9// Note how TWO r->o7 replaces were made here!
w -> d6 = d6o78o7d69  // and similarly w->d6 twice!

I think this gives you a clue as to what is happening -- the same effect will 
occur on your second str_replace, as well, giving you your apparent "multiple 
encode" problem. If you must do this kind of translation, then you need a 
function that doesn't have this re-replace effect, such as strtr() 
http://php.net/strtr.

But, I have to wonder, why aren't you just using one of the encoding functions 
readily available in PHP, such as md5() or sha1(), or hash()?


Cheers!

Mike
 -- 
Mike Ford,
Electronic Information Developer, Libraries and Learning Innovation,  
Leeds Metropolitan University, C507, Civic Quarter Campus, 
Woodhouse Lane, LEEDS,  LS1 3HE,  United Kingdom 
Email: m.f...@leedsmet.ac.uk 
Tel: +44 113 812 4730




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[PHP] running str_replace, it misbehaves!

[Allen McCabe]

Hi friends, I'm trying to get an encrypting program working to possibly use
for password insertion into a db.

I set up a function that runs str_replace on a string (user supplied) two
times. It searches for a single letter or number, and replace it with a
pair. The next str_replace searches that new string for different pairs, and
replaces them with a three-character string (symbol, character, character).
I'm using % as my symbol, so I'm pretty sure this isn't the issue.

It encodes, but the resulting string is way longer than expected!

I set sup a decode function, with the same str_replace values, just with the
replaces flipped. This works to return to me my original value, but I have
to decode about 6 times (after encoding once). Basically, running a string
through the encoding function will decode back to its original value, but I
have to run it through the decode function multiple times to do so.

Here is an example of my code:

[code]






  />


[/code]

I have a feeling that php is running the functions through the str_replace
functions multiple times. It doesn't seem to mess with the unique-ness I had
to build into it (in order to preserve the string for decoding), but it
makes me nervous if it runs it through multiple times. Does anyone know why
the encoding step results in such a long string? And why do I have to run
decode on the result so many times to change it back?

Any and all help would be greatly appreciated!