Lab Assignment #8

The due date is 11:30 a.m. on Friday, March 19. Hand in items using submit unless the problem says otherwise.

1. A more complete password suite

In computing, a suite means a set of interconnected entities that work together, just as a hotel suite is a set of interconnected rooms. For example, a ``software suite'' means a package such as Microsoft Office that has a number of related programs in it, working together. We could talk about a ``suite'' of interrelated web pages and CGI scripts to perform some function.

Improve your password page and CGI script by extending it to become a suite of pages and CGI scripts to do the following. Assume that you have first made an empty file user_data with an editor.

• Your entrance page should have some greeting and resemble typical sites that require visitors (users) to register. One such site is the London Times, at http://www.the-times.co.uk , where the entrance page asks first-time visitors to register via an anchor link and for previously registered visitors also provides boxes for an ID and password. The page warns the visitor that these are case-sensitive.
• If a visitor has not registered before, the link leads to a registration page that asks for visitor data. For your registration page,
  • Ask for last name, first name, a visitor ID and a password.
  • When the visitor clicks on a submit button, the CGI script must open and lock the user info file, read it to check that there is presently no visitor with the same ID, and close the file.
  • If this is a duplicate id, the visitor should get a page that says something like ``Duplicate ID--please click on the BACK button and choose a different ID''. If you want, you can use CGI output in the form Location:...with an actual HTML file.
  • If there is not already a visitor with that ID, then the script should open and lock the user info file for appending (">>user_info"), print to it a line with the visitor data and encrypted password (all separated by colons), and close the file.
  • When first getting the visitor data, the script should make sure there are no special characters in it, except for characters that could legitimately occur in a name field.
  • For encryption, have the salt be the first two letters of your first name.

• If the visitor has registered before, as shown by the visitor's clicking a ``submit'' button on the entrance page, the corresponding script should generate a virtual page saying ``Welcome [visitor's first and last names]''.
• Make your pages look moderately nice using tables, style sheets, etc. Don't go to too much trouble.
• A real site would also have a way to allow the visitor to change the password, as well as further pages, but that's not necessary for this assignment.

2. Numbers

(Not to hand in.)

Consider a ``toy'' Diffie-Hellman example with p = 11, g=2 (agreed on publicly by Alice and Bob). If Alice chooses private code x sub A = 9 and Bob chooses private code x sub B = 4, what are their public codes and what is their secret key?

3. XML

(a) Write a Perl script that reads the file h/rosterx and prints out the information in XML format, where each record has the form

<student>
   <SID> ... </SID>
   <name> ... </name>
   <email> ... </email>
   <major> ... </major>
</student>

If a field is blank, leave it blank.

(b) Write a Perl script that reads this format and puts it back in the form of h/rosterx . Your program should not rely on the newlines in the file, but just the tags. Some ideas will be given in discussion Tuesday.

4. Other

There will be one more easy task assigned.