Encoding and decoding strings using the ROT13 method
ROT13 is a commonly used method for encoding a text string so that it
cannot be easily read. This encoding process DOES NOT encrypt the text (so don't even
consider using it to encode passwords or other sensitive information). Nonetheless, it is
a useful method to use in certain situations. If you want to use sophisticated
encryption within ASP, then take a look at this article.
ROT13 uses a simple encoding process; the alphabet is rotated 13
characters, so that "a" becomes "n", "z" becomes
"m", "N" becomes "Y" and so on...
 |
Warning! |
| ROT13 is a simple encoding process, so it is not suitable for encrypting
sensitive information. |
ROT13 originated on USENET, so if you have added USENET support to your
ASP powered website then it is a particularly useful feature to build into the site.
Another possible use would be to encode Query Strings or non-sensitive
cookie data. Although it must be stressed that ROT13 does not encrypt text, it can be
effective in keeping the average user from figuring out how your site works. So if you
used ROT13 in your site, instead of something like...
http://www.foo.com/login.asp?user=freddy&dept=customer%20support
the Query String would become:
http://www.foo.com/login.asp?user=serqql&dept=phfgbzre%20fhccbeg
If you want to test ROT13 encoding, then enter some text into the box
below:
Encoding and decoding of ROT13 can be easily carried out by an ASP script
or a JavaScript. The script (written in VBScript, PHP, JScript and client side JavaScript)
is shown below.
VBScript
The VBScript function for encoding and decoding text using ROT13 is shown
below:
' rot13
function - a function to encode and decode text strings using the popular ROT13 method
' note that ROT13 does not encrypt strings, so do not use it if security is an issue!
Function rot13(rot13text)
rot13text_rotated = "" ' the function will return this
string
For i = 1 to Len(rot13text)
j = Mid(rot13text, i, 1) ' take the next character in the
string
k = Asc(j) ' find out the character code
if k >= 97 and k =< 109 then
k = k + 13 ' a ... m inclusive become n ... z
elseif k >= 110 and k =< 122 then
k = k - 13 ' n ... z inclusive become a ... m
elseif k >= 65 and k =< 77 then
k = k + 13 ' A ... M inclusive become N ... Z
elseif k >= 78 and k =< 90 then
k = k - 13 ' N ... Z inclusive become A ... M
end if
'add the current
character to the string returned by the function
rot13text_rotated = rot13text_rotated & Chr(k)
Next
rot13 = rot13text_rotated
End Function
The function can then be called from an ASP page by using something like:
Response.Write rot13("Hello World")
or
<%=rot13(my_department)%>
Don't forget that the same function is used to both encode and decode
ROT13.
JavaScript
It is also possible to use ROT13 encoding with JavaScript. The function
below uses JavaScript to convert strings using the ROT13 method. It has been tested and
found to work in Internet Explorer 5 and Netscape 4.5.
<script LANGUAGE="JavaScript">
function JSrot13(text) {
var rot13text_rotated = ""; /* the function will
return this string */;
for (i = 1 ; i < (text.length + 1); i++) {
k = text.charCodeAt(i-1);
if (k >= 97 && k <= 109) {
k = k + 13;
} else
if (k >= 110 && k <= 122) {
k = k - 13;
} else
if (k >= 65 && k <= 77) {
k = k + 13;
} else
if (k >= 78 && k <= 90) {
k = k - 13;
}
rot13text_rotated = rot13text_rotated + String.fromCharCode(k);
}
return rot13text_rotated;
}
</script>
Once you have added the function to the page, it can be called using something like:
<script language="JavaScript">
document.write (JSrot13("Visit ASPAlliance.com for some great original ASP
articles!"));
</script>
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Author details
Brett Burridge
has worked as a web developer since 1997 and has developed web applications for a range of corporations, start up busiensses and educational establishments.
Brett is presently employed as an Internet developer and technical writer
through his own company,
Winnersh Triangle Web Solutions Limited.
The company produces a number of
innovative products, including a range of software documentation tools, which include the
ASP Documentation Tool™, the .NET Documentation Tool for VB.NET and C#, and the SQL Server Documentation Tool. Other products include The Website Utility, which functions as a website error checker, search engine optimizer and ASP/ASP.NET search engine builder application.
As well as the ASPAlliance, Brett has written articles for Ariadne.ac.uk,
ASPToday, the software documentation portal www.softwaredocumentation.info, and has contributed recipes to the ASP.NET Developer's Cookbook.
links
Outside web development, Brett is interested in travelling (here are my travel logs from New York, Hong Kong and Tokyo), digital photography (here's my photo gallery), tropical fishkeeping
and collecting contemporary works of art by artists such as Doug Hyde.
Contact Brett by emailing
Article history
"Encoding and decoding strings using the ROT13 method" originally published
on ASPWatch.com on September 8 1999. Republished on ASPAlliance.com on 29 September 2001.
Last revised 16 May 2003.
ASP Kitchen: ASPWatch.com
articles: ROT13 Encoding Using ASP
|
