Hexadecimal equivalent codes of ASCII characters can be used to represent characters of a URL’s path and filename.

Each hex number is preceded by a “%” symbol to identify the following two numbers/letters as a hexadecimal representation of the character

An ASCII chart can be used for the conversion from ASCII to Hex or vice versa

One good source for ASCII to Hex charts is http://en.wikipedia.org/wiki/ASCII (both the tables below have been taken from this URL)

The need for typing in Hex codes into a URL is to make it possible to include special characters in a URL which would otherwise be wrongly interpreted or not allowed. A good example is SPACE which would not be able to fit into a URL in its original form and hence is represented by the Hex code 20 (prefixed by % in a URL making it %20)

For example, if we were to visit the URL www.bing.com , it could be written as

B =  %42

I = %49

N = %4e

G = %47

Hence, www.bing.com could be written as www.%42%49%4e%47.com

Note: The “slashes” in the address cannot be represented in hex; nor can the IP address be rendered using this logic (the %XX way) but the rest of the URL can be manipulated

We all know IP addresses to be of the form XX.XX.XX.XX where XX is an octet ranging from 1 to 255 (Although other rules apply as to what the value of XX could be depending on either of the four octets)

However, for users who want to obscure the actual IP address can do so by representing them in serveral other formats. Some of the formats are:

1. Decimal System

The traditional format that we know of is 192.168.1.1 where 4 decimal numbers are seperated by dots (.)

I will practically demonstrate converting between the different formats with a live example www.bing.com

C:\>ping bing.com

Pinging bing.com [64.4.8.147] with 32 bytes of data:

Request timed out.
Request timed out.
Request timed out.
Request timed out.

Ping statistics for 64.4.8.147:
    Packets: Sent = 4, Received = 0, Lost = 4 (100% loss),

Here the Decimal System version of the IP address 64.4.8.147 , this is represented in the base 10 system. Typing http://64.4.8.147 in the browser would also take you to www.bing.com

2. Octal System

An IP address represented in the octal system is basically in the base-8 system

64.4.8.147  would be broken down into

64 = 100 (octal)

4 = 4 (octal)

8 = 10 (octal)

147 = 223 (octal)

Hence the IP address in Octal format would be 0100.04.010.0223 (for those people who hate 0′s and 1′s, the same conversion can be easily done using the Windows Calculator)

Note: A single leading zero has been added to every octal number above, however any number of leading zeroes can be added (there is however a limit, some browsers won’t accept lots of zeroes)

Hence, 0100.04.010.0223 is the same as 00100.004.0010.00223 and www.bing.com can also be written as http://0100.04.010.0223

3. Domain Name System

Here the IP address is represented in its equivalent domain name using human recognizable characters. In our example, the DNS equivalent would be www.bing.com

4. Hexadecimal System

To convert a decimal IP address into its hexadecimal equivalent, break the ip address into its individual octets. Let us take out example above 64.4.8.147

64 = 40 (hex)

4 = 04 (hex)

8 = 08 (hex)

147 = 93 (hex)

Hence, 64.4.8.147 is equivalent to 0×40040893, the 0x is prefixed to indicate hexadecimal. Typing http://ox40040893 into the browser would take you to the bing website also

5. Double Word (DWORD)

To understand this format, we first need to understand what a double word is. A word consists of 16 binary digits (bits) and a double word consists of 32 bits

 To convert a decimal IP address into DWORD format, we first need to convert it into Hexadecimal and then convert the hexadecimal number to base 10

From point 4 (decimal to hex conversion) above we can see that the Hex equivalent of our sample IP address, 64.4.8.147 is 0×40040893

Now to convert this Hexadecimal number to DWORD, one of the easiest ways is to use the Windows Calculator

Click on Start > Programs > Accessories > Calculator
Click on View > Scientific
Now, select ‘Hex’ from the left top corner and type in the hex value in the field
Then click on Dec (Decimal). You will find that the value that you typed in would have changed to the corresponding value

Hence the equivalent DWORD value as per the diagram is 1074006163 and entering http://1074006163 into the browser would also take you to www.bing.com

6. Hybrid/Mixed

Last but not least, we have another format that is a continental cocktail of two or more of the formats above. In other words, we can mix decimal and hex in one ip address or anything that you can think of

For example, IP address formats

Decimal   64.4.8.147

Hexadecimal   0×40040893

DWORD   1074006163

I can mix the decimal and the hexadecimal as in http://64.0×04.0×08.147/

I can also mix and match more than 2 formats (hex, decimal, octal) as in http://64.0×04.8.0223

Expressing characters in the URL in Hexadecimal format

An ASCII to Hex Chart can be used to represent letters in the URL in Hex format

For the complete chart and more information, an excellent resource is

http://en.wikipedia.org/wiki/ASCII

WARNING: The obscured URL’s do not work in all browsers of all types and versions, internet explorer is pretty flexible, however netscape and firefox are crancky from my experience with URL’s in different formats

To summarize, URL’s can be obscured by converting IP address from the traditional decimal format to any of the other formats mentioned like DWORD, Octal, Hexadecimal, etc. In addition, characters in a URL can be expressed as numbers in hexadecimal format