<?php
/**
* $string Plaintext or ciphertext
* $operation encryption ENCODE Or decrypt DECODE
* $key The key
* $expiry Key validity period
*/
function authcode($string, $operation = 'DECODE', $key = '', $expiry = 0) {
// Dynamic key length, same plaintext will generate different ciphertext depending on the dynamic key
// Adding a random key can make the ciphertext irregular. Even if the original text and the key are exactly the same, the encryption results will be different each time, increasing the difficulty of cracking.
// The larger the value is, the larger the ciphertext variation law is, and the ciphertext changes = 16 the $ckey_length To the power
// When this value is 0 , no random key is generated
$ckey_length = 4;
// The key
// $GLOBALS['discuz_auth_key'] This can be modified according to your own needs
$key = md5($key ? $key : $GLOBALS['discuz_auth_key']);
// The key a Will participate in the decryption
$keya = md5(substr($key, 0, 16));
// The key b Will be used for data integrity verification
$keyb = md5(substr($key, 16, 16));
// The key c Ciphertext for change generation
$keyc = $ckey_length ? ($operation == 'DECODE' ? substr($string, 0, $ckey_length): substr(md5(microtime()), -$ckey_length)) : '';
// The key that takes part in the operation
$cryptkey = $keya.md5($keya.$keyc);
$key_length = strlen($cryptkey);
// Before the clear, 10 Bits are used to hold timestamps, verify data validity when decrypting, 10 to 26 Bits for storing $keyb( The key b) This key is used to verify data integrity when decrypted
// If it's decoding, it's going to start at number one $ckey_length Bits start as ciphertext precedes $ckey_length A save Dynamic key to ensure correct decryption
$string = $operation == 'DECODE' ? base64_decode(substr($string, $ckey_length)) : sprintf('%010d', $expiry ? $expiry + time() : 0).substr(md5($string.$keyb), 0, 16).$string;
$string_length = strlen($string);
$result = '';
$box = range(0, 255);
$rndkey = array();
// Generate the keybook
for($i = 0; $i <= 255; $i++) {
$rndkey[$i] = ord($cryptkey[$i % $key_length]);
}
// Using a fixed algorithm, shuffling the keybook, increasing randomness, seems complicated, but it doesn't actually increase the strength of the ciphertext
for($j = $i = 0; $i < 256; $i++) {
$j = ($j + $box[$i] + $rndkey[$i]) % 256;
$tmp = $box[$i];
$box[$i] = $box[$j];
$box[$j] = $tmp;
}
// Core encryption and decryption part
for($a = $j = $i = 0; $i < $string_length; $i++) {
$a = ($a + 1) % 256;
$j = ($j + $box[$a]) % 256;
$tmp = $box[$a];
$box[$a] = $box[$j];
$box[$j] = $tmp;
// Get the key from the keybook for xor, and then convert to characters
$result .= chr(ord($string[$i]) ^ ($box[($box[$a] + $box[$j]) % 256]));
}
if($operation == 'DECODE') {
// substr($result, 0, 10) == 0 Verify data validity
// substr($result, 0, 10) - time() > 0 Verify data validity
// substr($result, 10, 16) == substr(md5(substr($result, 26).$keyb), 0, 16) Verify data integrity
// To verify the validity of the data, see unencrypted plaintext format
if((substr($result, 0, 10) == 0 || substr($result, 0, 10) - time() > 0) && substr($result, 10, 16) == substr(md5(substr($result, 26).$keyb), 0, 16)) {
return substr($result, 26);
} else {
return '';
}
} else {
// Keep the dynamic key in ciphertext, which is why the same plaintext can be decrypted by producing different ciphertext
// Because the encrypted ciphertext could be 1 Some special characters may be lost in the copying process, so use base64 coding
return $keyc.str_replace('=', '', base64_encode($result));
}
}
$a = www.ofstack.com;
$b = authcode($a, "ENCODE", "abc123");
echo $b."<br/>";
echo authcode($b, "DECODE", "abc123");
?>