实例应用：使用PHP来进行加密与解密

haidong

<>&lt;?php <BR>$key = "This is supposed to be a secret key !!!"; <BR>function keyED($txt,$encrypt_key) <BR>{ <BR>$encrypt_key = md5($encrypt_key); <BR>$ctr=0; <BR>$tmp = ""; <BR>for ($i=0;$i&lt;strlen($txt);$i++) <BR>{ <BR>  if ($ctr==strlen($encrypt_key)) $ctr=0; <BR>  $tmp.= substr($txt,$i,1) ^ substr($encrypt_key,$ctr,1); <BR>  $ctr++; <BR>} <BR>return $tmp; <BR>} <BR>function encrypt($txt,$key) <BR>{ <BR>srand((double)microtime()*1000000); <BR>$encrypt_key = md5(rand(0,32000)); <BR>$ctr=0; <BR>$tmp = ""; <BR>for ($i=0;$i&lt;strlen($txt);$i++) <BR>{ <BR>  if ($ctr==strlen($encrypt_key)) $ctr=0; <BR>  $tmp.= substr($encrypt_key,$ctr,1) . <BR>  (substr($txt,$i,1) ^ substr($encrypt_key,$ctr,1)); <BR>  $ctr++; <BR>} <BR>return keyED($tmp,$key); <BR>} <BR>function decrypt($txt,$key) <BR>{ <BR>$txt = keyED($txt,$key); <BR>$tmp = ""; <BR>for ($i=0;$i&lt;strlen($txt);$i++) <BR>{ <BR>  $md5 = substr($txt,$i,1); <BR>  $i++; <BR>  $tmp.= (substr($txt,$i,1) ^ $md5); <BR>} <BR>return $tmp; <BR>} <BR>$string = "Hello World !!!"; <BR>// encrypt $string,_and_store it in $enc_text <BR>$enc_text = encrypt($string,$key); <BR>// decrypt the encrypted text $enc_text,_and_store it in $dec_text <BR>$dec_text = decrypt($enc_text,$key); <BR>print "Original text : $string &lt;Br&gt;"; <BR>print "Encrypted text : $enc_text &lt;Br&gt;"; <BR>print "Decrypted text : $dec_text &lt;Br&gt;";<BR>?&gt;</P>