Share a piece of php encryption and decryption code

Sometimes in the project we need to use PHP to encrypt specific information, that is, an encrypted string is generated through the encryption algorithm. This encrypted string can be decrypted through the decryption algorithm, which is convenient for the program to The decrypted information is processed.
The most common applications are user login and some API data exchange scenarios.

The most common applications are in user login and some API data exchange scenarios.
The author has collected some classic PHP encryption and decryption function codes to share with you. The principle of encryption and decryption is generally to use a certain encryption and decryption algorithm, add the key to the algorithm, and finally obtain the encryption and decryption results.

<?php  
$key = "This is supposed to be a secret key !!!";  

function keyED($txt,$encrypt_key)  
{  
$encrypt_key = md5($encrypt_key);  
$ctr=0;  
$tmp = "";  
for ($i=0;$i<strlen($txt);$i++)  
{  
if ($ctr==strlen($encrypt_key)) $ctr=0;  
$tmp.= substr($txt,$i,1) ^ substr($encrypt_key,$ctr,1);  
$ctr++;  
}  
return $tmp;  
}  

function encrypt($txt,$key)  
{  
srand((double)microtime()*1000000);  
$encrypt_key = md5(rand(0,32000));  
$ctr=0;  
$tmp = "";  
for ($i=0;$i<strlen($txt);$i++)  
{  
if ($ctr==strlen($encrypt_key)) $ctr=0;  
$tmp.= substr($encrypt_key,$ctr,1) .  
(substr($txt,$i,1) ^ substr($encrypt_key,$ctr,1));  
$ctr++;  
}  
return keyED($tmp,$key);  
}  

function decrypt($txt,$key)  
{  
$txt = keyED($txt,$key);  
$tmp = "";  
for ($i=0;$i<strlen($txt);$i++)  
{  
$md5 = substr($txt,$i,1);  
$i++;  
$tmp.= (substr($txt,$i,1) ^ $md5);  
}  
return $tmp;  
}  

$string = "Hello World !!!";  

// encrypt $string, and store it in $enc_text  
$enc_text = encrypt($string,$key);  

// decrypt the encrypted text $enc_text, and store it in $dec_text  
$dec_text = decrypt($enc_text,$key);  

print "Original text : $string <Br>\n";  
print "Encrypted text : $enc_text <Br>\n";  
print "Decrypted text : $dec_text <Br>\n";  
?>

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