URL encoding &&php Dafa

URL encoding

URL encoding is also commonly referred to as a percent-encoding (URL encoding,also known as percent-encoding) because it is encoded in a very simple way, using the% percent sign plus the two-bit character--0123456789abcdef-- Represents a 16 binary form of a byte. The default character set used by URL encoding is US-ASCII. For example A in the US-ASCII code in the corresponding byte is 0x61, then the URL encoding is%61, we enter http://g.cn/search?q=%61%62%63 on the address bar, in fact, the equivalent of searching for ABC on google. Another example of the @ symbol in the ASCII character set of the corresponding byte is 0x40, after the URL encoded by the%40.

For non-ASCII characters, a superset of the ASCII character set is required to encode the corresponding bytes, and then the percent code is executed for each byte. For Unicode characters, the RFC document recommends using UTF-8 to encode the corresponding bytes, and then perform a percent-encoding on each byte. For example, "Chinese" uses the UTF-8 character set to get the byte 0xe4 0xb8 0xAD 0xe6 0x96 0x87, after URL encoding to get "%e4%b8%ad%e6%96%87".

If a byte corresponds to a non-reserved character in the ASCII character set, this byte does not need to be represented by a percent sign. For example, "URL encoding", the bytes obtained using UTF-8 encoding is 0x55 0x72 0x6c 0xE7 0xBC 0x96 0xE7 0xA0 0x81, because the first three bytes correspond to the non-reserved character "url" in ASCII, so these three bytes can be used non-reserved character "url" Said. The final URL encoding can be simplified to "url%e7%bc%96%e7%a0%81", of course, if you use "%55%72%6c%e7%bc%96%e7%a0%81" is also possible.

PHP Dafa

<? PHPif(Eregi ("Hackerdj", $_get[id])) {Echo ("<p>not allowed!</p>"); Exit ();} $_get[id]=UrlDecode ($_get[id]);if($_get[id] = ="Hackerdj") {echo"<p>access granted!</p>"; Echo"<p>flag: *****************} </p>";}?><br><br>Can You authenticate to this website?

If the ID=HACKERDJ does not output flag but the decoded ID=HACKERDJ can output flag

The encoding for%25,H is encoded as%68, so the%2568 is combined,

So payload:

Http://ctf5.shiyanbar.com/DUTCTF/index.php?id=%2568ackerDJ

Get flag:

URL encoding &&php Dafa