The idea and implementation code of generating SessionID and image verification code in php_PHP tutorial

/****** Generate Session ID ******/
The basic idea is to obtain the current microsecond time, then generate a random number, add the random number to the current time and encrypt it, and finally intercept the required length
/*
Function name: create_sess_id()
Function function: Generate a random session ID
Parameter: $len: The length of the session string is required, the default is 32 bits, not less than 16 Bit
Return value: Return session ID
Function author: heiyeluren
*/
function create_sess_id($len=32)
{
// Verify whether the submitted length is legal
if( !is_numeric($len) || ($len>32) || ($len// Get the microseconds of the current time
list($u, $s) = explode(' ', microtime());
$time = (float)$u + (float)$s;
// Generate a random number
$rand_num = rand(100000 , 999999);
$rand_num = rand($rand_num, $time);
mt_srand($rand_num);
$rand_num = mt_rand();
// Generate SessionID
$sess_id = md5( md5($time). md5($rand_num) );
//Intercept the SessionID of the specified required length
$sess_id = substr($sess_id, 0, $len);
return $sess_id ;
}


/****** Generate verification code ******/
Idea: This idea is relatively simple, because considering uniqueness and randomness, our verification code intercepts a segment from the Session ID A string is fine because our SessionID is fully considered unique.

/*
Function name: create_check_code()
Function function: Generate a random check code
Parameters: $len: The length of the check code required, please not be longer than 16 digits, the default is 4 digits
Return value: Returns the check code of the specified length
Function author: heiyeluren
*/
function create_check_code($len=4)
{
if ( !is_numeric($len) || ($len>6) || ($len
$check_code = substr(create_sess_id(), 16, $len );
return strtoupper($check_code);
}


/****** Picture of generating verification code ******/

This is some relatively simple PHP image programming stuff. I made the pictures simple and simple.

/*
Function name: create_check_image()
Function function: generate a check code image
Parameters: $check_code: Check code string, generally used by create_check_code() function To get the
return value: return the image
Function author: heiyeluren
*/
function create_check_image( $check_code )
{
// Generate an image
$im = imagecreate(65,22);
$black = ImageColorAllocate($im, 0,0,0); // Background color
$white = ImageColorAllocate($im, 255,255,255); // Foreground color
$gray = ImageColorAllocate($im, 200,200,200);
imagefill($im,68,30,$gray);

// Draw the four-digit integer verification code into the image
imagestring($ im, 5, 8, 3, $check_code, $white);
//Add interference pixels
for($i=0;$i{
$ randcolor = ImageColorallocate($im,rand(0,255),rand(0,255),rand(0,255));
imagesetpixel($im, rand()%70 , rand()%30 , $randcolor);
}
//Output image
Header("Content-type: image/PNG");
ImagePNG($im);
ImageDestroy($im);
}

Here we should note that when referencing the create_check_image() function, it must be in a separate file, because the output format when outputting the file header is an image format, and mixed with other content, the image will not be displayed. In addition, you can change the image generation function. For example, if you want to change the color, then you change the generation positions of the foreground color and background color, then the colors will be different. At the same time, you also need to change the color of the check code. Change it, otherwise the background and check code will be black and will not be displayed.

http://www.bkjia.com/PHPjc/319940.htmlwww.bkjia.comtruehttp: //www.bkjia.com/PHPjc/319940.htmlTechArticle/****** Generate Session ID ******/ The basic idea is to obtain the current microsecond time, and then generate the following A random number, add the random number to the current time, encrypt it, and finally intercept it...