本帖最后由 xuzuning 于 2013-02-21 10:07:35 编辑 现在已知一解密函数（readkey）如下，求对应的加密函数
<br>function authcode( $string, $operation = "DECODE", $key = "", $expiry = 0 )<br>{<br> $ckey_length = 4;<br> $key = md5( $key != "" ? $key : "a2264dxLupVMlkqR" );<br> $keya = md5( substr( $key, 0, 16 ) );<br> $keyb = md5( substr( $key, 16, 16 ) );<br> $keyc = $ckey_length ? $operation == "DECODE" ? substr( $string, 0, $ckey_length ) : substr( md5( microtime( ) ), 0 - $ckey_length ) : "";<br> $cryptkey = $keya.md5( $keya.$keyc );<br> $key_length = strlen( $cryptkey );<br> $string = $operation == "DECODE" ? base64_decode( substr( $string, $ckey_length ) ) : sprintf( "%010d", $expiry ? $expiry + time( ) : 0 ).substr( md5( $string.$keyb ), 0, 16 ).$string;<br> $string_length = strlen( $string );<br> $result = "";<br> $box = range( 0, 255 );<br> $rndkey = array( );<br> $i = 0;<br> for ( ; $i {<br> $rndkey[$i] = ord( $cryptkey[$i % $key_length] );<br> }<br> $j = $i = 0;<br> for ( ; $i {<br> $j = ( $j + $box[$i] + $rndkey[$i] ) % 256;<br> $tmp = $box[$i];<br> $box[$i] = $box[$j];<br> $box[$j] = $tmp;<br> }<br> $a = $j = $i = 0;<br> for ( ; $i {<br> $a = ( $a + 1 ) % 256;<br> $j = ( $j + $box[$a] ) % 256;<br> $tmp = $box[$a];<br> $box[$a] = $box[$j];<br> $box[$j] = $tmp;<br> $result .= chr( ord( $string[$i] ) ^ $box[( $box[$a] + $box[$j] ) % 256] );<br> }<br> if ( $operation == "DECODE" )<br> {<br> if ( ( substr( $result, 0, 10 ) == 0 || 0 {<br> return substr( $result, 26 );<br> }<br> return "";<br> }<br> return $keyc.str_replace( "=", "", base64_encode( $result ) );<br>}<br>function readkey( $keys )<br>{<br> $Leskey = authcode( $keys, "DECODE", "a2264dxLupVMlkqR" );<br> $Leskey = base64_decode( $Leskey );<br> $firstStr = substr( $Leskey, 0, 1 );<br> $Leskey = substr( $Leskey, 1 );<br> $Leskey = strrev( substr( $Leskey, 0, $firstStr ) ).chr( ord( substr( $Leskey, $firstStr, 1 ) ) ^ $firstStr ).strrev( substr( $Leskey, $firstStr + 1 ) );<div class="clear">
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