[RESOLVED] MCRYPT / GD Issue

[schajee]

Hi, I'm trying to get a form image verification program to work (everytime) but occasionally it happens that i get garbled text in the image generated through GD. I was wondering if this was a GD issue or MCRYPT or worse my coding. I'm attaching the code below...

// functions.php

function get_number($size){
	$characters = "BCDFGHJKLMNRSTVXY2457";
	$output = "";
	for ($i=0; $i<$size; $i++)
		$output .= $characters{rand()%(strlen($characters))};
	return $output;
}

function encrypt ($input) {
    $iv_size = mcrypt_get_iv_size(MCRYPT_3DES, MCRYPT_MODE_ECB);
    $iv = mcrypt_create_iv($iv_size, MCRYPT_RAND);
    $crypttext = mcrypt_encrypt(MCRYPT_3DES, SECRET_CODE, $input, MCRYPT_MODE_ECB, $iv);
	$crypttext = urlencode($crypttext);
	return $crypttext;
}

function decrypt ($input) {
	$input = urldecode ($input);
    $iv_size = mcrypt_get_iv_size(MCRYPT_3DES, MCRYPT_MODE_ECB);
    $iv = mcrypt_create_iv($iv_size, MCRYPT_RAND);
    $decrypttext = rtrim(mcrypt_decrypt(MCRYPT_3DES, SECRET_CODE, $input, MCRYPT_MODE_ECB, $iv));
	return $decrypttext;
}

//image.php

function create_image ($input) {

$img = imagecreatefrompng("images/bg.png");

$white = imagecolorallocate($img,255,255,255);
$black = imagecolorallocate($img,0,0,0);

$i=1;
while ($i<=strlen($input)) {
	Imagettftext($img, 20,rand(-30,30),$i*25,33,$black,'courbd.ttf',$input{$i-1});
	$i++;
}

imagepng($img);
imagedestroy($img);
}

create_image (decrypt($_GET['q']));

Here's how it works...

I'm calling the image.php program with a

?q=encrypt(get_number(5))

where create_image decrypts the input text and generates the desired image.

Sometimes (once in say 10-15 tries) there is garbled text on the image generated by GD.

Any help would be nice.

[bpat1434]

I'm thinking it has something to do with your character selection. Try this:

function get_number($size){
	$characters = "BCDFGHJKLMNRSTVXY2457";
	$output = "";
	for ($i=0; $i<$size; $i++)
		$output .= $characters{rand(0, strlen($characters)-1)};
	return $output;
}

[schajee]

Nopes....... still there

I was also thinking maybe its the font. Maybe I should try to design my own font before I try it in something like this. I know this is too early but who knows.

[bpat1434]

Well, I tested your code a bit, and it would seem that it's in the text that's the issue. Have you looked at the font? Does it include all the letters you have (it should if it's a complete font)? Everything else works fine for me locally.

[schajee]

Well as it says, I was using "courbd.ttf" which is Courier Bold and I would be extremely surprised if it didn't have these characters in it. I've tried with fonts of all kinds, but the results are the same.

For those who wanna see what is going on

[bpat1434]

Then it seems that the decryption doesn't work in all cases. Something happens, not sure what. Perhaps it's not being decoded entirely properly. The reason I think this is because of this line:

Imagettftext Manual wrote:

If a character is used in the string which is not supported by the font, a hollow rectangle will replace the character.

[schajee]

Hollow rectangle is easily understandable, when the decrypt doesn't do its job. But right now I'm going through the process of debugging inside the image generator which is quite tedious as I have to view source every time to see if things are working properly or not.

I'll report back on the debugging.

[schajee]

I've just spent quite a lot of time debugging using this code. The problem is i don't see any problems. But right now it doesn't look like an MCRYPT or GD issue. So what is the problem? :rolleyes:

<?php 

define ('SECRET_CODE', 'secretcode');
print "<h3>Generating...</h3>";
$textnum = get_number(5);
print "<p>$textnum</p>";
$textenc = encrypt($textnum);
$image = create_image(decrypt($textenc));
print "<img src='temp.png'>";

function get_number($size){
    $characters = "BCDFGHJKLMNRSTVXY2457";
    $output = "";
    for ($i=0; $i<$size; $i++)
        $output .= $characters{rand(0, strlen($characters)-1)};
    return $output;
} 

function encrypt ($input) {
	print "<h3>Encrypting...</h3>";
    $iv_size = mcrypt_get_iv_size(MCRYPT_3DES, MCRYPT_MODE_ECB);
    $iv = mcrypt_create_iv($iv_size, MCRYPT_RAND);
    $crypttext = mcrypt_encrypt(MCRYPT_3DES, SECRET_CODE, $input, MCRYPT_MODE_ECB, $iv);
	print "<p>$crypttext</p>";
	print "<h3>URL Encoding...</h3>";
	$crypttext = urlencode($crypttext);
	print "<p>$crypttext</p>";
	return $crypttext;	
}

function decrypt ($input) {
	print "<h3>URL Decoding...</h3>";	
	$input = urldecode ($input);
	print "<p>$input</p>";
    $iv_size = mcrypt_get_iv_size(MCRYPT_3DES, MCRYPT_MODE_ECB);
    $iv = mcrypt_create_iv($iv_size, MCRYPT_RAND);
    $decrypttext = rtrim(mcrypt_decrypt(MCRYPT_3DES, SECRET_CODE, $input, MCRYPT_MODE_ECB, $iv));
    print "<h3>Decrypting...</h3>";	
    print "<p>$decrypttext</p>";
	return $decrypttext;
}

function create_image ($input) {

print "<h3>Generating Image...</h3>";
$img = imagecreatefrompng("images/bg.png");

$white = imagecolorallocate($img,255,255,255);
$black = imagecolorallocate($img,0,0,0);

$i=1;
while ($i<=strlen($input)) {
	Imagettftext($img, 20,rand(-30,30),$i*25,33,$black,'courbd.ttf',$input{$i-1});
	$i++;
}

//	header ("Content-type:image/png");
	imagepng($img, "temp.png");
	imagedestroy($img);
}

?>

[bpat1434]

i think i figured it out. If you look closely at the urlencoded stuff, it doesn't seem to be working quite right. Not sure why. But if you rawurlencode it after the encrypt function returns the value, it seems to work flawlessly.

	echo '<strong>Generating . . .</strong><br />';
	$textnum = get_number(5);
	echo '<strong>Number: </strong> ', $textnum, '<br />';
	$enced = encrypt($textnum);

echo '<a href="?q=', rawurlencode($enced), '">Click Here to Proceed</a>';

That works for me every time. No missed characters. Not sure what to tell you. Maybe to just urlencode it outside the function. For whatever reason, it doesn't want to return the URL encoded value to me.

[schajee]

NICE!!! 😃 Works like a charm.

I have yet to notice the difference between rawurl and url encoding, but apparently its working fine. I'll keep a log to see if i ever get a mismatch.

[schajee]

CONCLUSION:

Somewhere, somewhere in between

?q=encrypt(get_number(5))

or

create_image (decrypt($_GET['q']));

or

$crypttext = urlencode($crypttext);
return $crypttext;

or

function decrypt ($input) {
$input = urldecode ($input);

urldecoded values were not being forwarded properly.

Previously, url encoding and decoding was taking place INSIDE the encrypt and decrypt functions.

RESOLUTION:

Moving the url encoding and decoding OUTSIDE the encrypt/decrypt functions resolved the issue (GARBLED TEXT IN IMAGES GENERATED VIA GD AFTER BEING FORWARDED THE VALUES FROM ENCRYPT AND DECRYPT FUNCTIONS)

[schajee]

[FONT=Courier New]The following code is being made available as the final resolution (of sorts) of issue raised in PHP Builder Forums Thread http://phpbuilder.com/board/showthread.php?t=10334546

The objective of this code was to genarate an image based on a randomly generated sequence of characters for use in verification of form submission. The code was originally intended (and used) for some other purposes and has been modified here to be self-contained for better usability.

Code here is being released under whichever license you wish 🙂[/FONT]

<?php	
//	BEGIN_SCRIPT

//	Define the key to be used in Encryption/Decryption procedures
define ('SECRET_CODE', 'secretcode');		
define ('ENC_METHOD', MCRYPT_3DES);
define ('ENC_MODE', MCRYPT_MODE_ECB);
define ('IV_SIZE', mcrypt_get_iv_size(ENC_METHOD, ENC_MODE));
define ('IV', mcrypt_create_iv(IV_SIZE, MCRYPT_RAND));
define ('SEQUENCE_SIZE', 5);
define ('IMAGE_FILE', 'temp.png');
define ('SOURCE_IMAGE', 'images/bg.png');
define ('FONT_FILE', 'courbd.ttf');


/*
The following can take place in another file (e.g. registration forms) for generating the final sequence to be use in <img src="this_file.php?q=encoded_encrypted_sequence">. The encoded_encrypted_text should also be placed in a hidden field inside the form. The field will be used as basis of comparison with text entered via textbox. 
*/

print "<h3>Generating...</h3>";
//	Generated a random sequence of size SEQUENCE_SIZE 
$sequence = get_number(SEQUENCE_SIZE);
print "<p>$sequence</p>";

print "<h3>Encrypting...</h3>";
//	Encrypt the generated sequence
$encrypted_sequence = encrypt($sequence);
print "<p>$encrypted_sequence</p>";

print "<h3>Encoding...</h3>";
// URLENCODE or RAWURLENCODE the encrypted sequence
$encoded_encrypted_sequence = urlencode($encrypted_sequence);
print "<p>$encoded_encrypted_sequence</p>";

/*
The following takes place inside the image generator to first decode, decrypt and then generate the image based on the sequence forwarded via the request <img src="this_file.php?q=encoded_encrypted_sequence">
*/

print "<h3>Decoding...</h3>";	
//	Decode the final sequence received via HTTP request (original idea)
$decoded_encrypted_sequence = urldecode ($encoded_encrypted_sequence);
print "<p>$decoded_encrypted_sequence</p>";

print "<h3>Decrypting...</h3>";	
//	Decrypt the decoded sequence 
$decoded_decrypted_sequence = decrypt($decoded_encrypted_sequence);
print "<p>$decoded_decrypted_sequence</p>";

print "<h3>Generating Image...</h3>";	
//	Generate the image from the decoded_decrypted_sequence using the create_image function 
$image = create_image($decoded_decrypted_sequence);
print "<img src='temp.png'>";

/*
The following section contains the four functions used in this program. 
*/

//	Generates a random sequence of size SEQUENCE_SIZE
function get_number(){
	//	Define a set of characters to be used in the sequence
    $characters = "BCDFGHJKLMNRSTVXY2457";
    //	Set output to NULL (Good practice)
    $output = "";
    //	Loop until SEQUENCE_SIZE is achieved
    for ($i=0; $i<SEQUENCE_SIZE; $i++)
    	//	Concatenate a randomly selected character from the sequence to the output
        $output .= $characters{rand(0, strlen($characters)-1)};
	//	Return the generated sequence
    return $output;
} 

//	Encrypts the input value
function encrypt ($input) {
    //	Encrypt input text using selected encryption
    $crypttext = mcrypt_encrypt(ENC_METHOD, SECRET_CODE, $input, ENC_MODE, IV);
    //	Return encrypted text
	return $crypttext;	
}

//	Decrypts the input value
function decrypt ($input) {
	//	Decrypt input text using seleted encryption
    $decrypttext = rtrim(mcrypt_decrypt(ENC_METHOD, SECRET_CODE, $input, ENC_MODE, IV));
    //	Return decrypted text
	return $decrypttext;
}

//	Generates the image based on the input sequence received
function create_image ($input) {
	//	Create image based on a source template, used as background
	$img = imagecreatefrompng(SOURCE_IMAGE);
	//	Set font color
	$black = imagecolorallocate($img,0,0,0);

//	$i was set to 1 to enable the x-pos to not start from 0
$i=1;
//	While sequence not complete
while ($i<=strlen($input)) {
	//	Place text in the image, use PHP reference for more details on this function
	Imagettftext($img, 20,rand(-30,30),$i*25,33,$black,FONT_FILE,$input{$i-1});
	$i++;
}

//	Place the generated image in the file IMAGE_FILE
//	Do not use image file when requesting via <img src="this_file.php?q=encoded_encrypted_sequence">
//	Just remove IMAGE_FILE
imagepng($img, IMAGE_FILE);

//	Destroy image, clear memory
imagedestroy($img);
}
//	END_SCRIPT
?>