SECRET AGENT

by JOHN SMITH

This BASIC listing turns your Atari into an impressive cryptographic machine.  You get menu-driven software that lets you automatically encode and decode secret messages.  Runs on all Atari computers of any memory size.

Secret messages fascinate people. Kids like to write to their pals in codes or invisible ink. Diplomats, military men and spies disguise important communications behind ciphers. Secret messages give a rare feeling of privacy to our communications. We can enjoy sharing secrets with friends and fellow insiders, excluding the rest of the world.
  For a more immediate practical use, this program can ensure the privacy of computer messages you leave for friends on bulletin boards or electronic mail services. One of the things Secret Agent will do is convert existing disk or cassette text files into secret code.

WHAT IT DOES
Suppose you want to send this order to the commander of your fleet:

ATTACK PEARL HARBOR AT DAWN!

  You have previously agreed on a secret keyword: HONDA. You enter your keyword, which can include 25 characters. Then you enter your message, up to 2,000 characters long. For the message and keyword, you can use capital letters, numbers and punctuation marks. But the program can't accept lower case, inverse video or Atari control characters.
  Secret Agent automatically encodes the text and writes it to your choice of screen, printer, disk, or cassette. The cipher for our sample message would read:

[N-,JIX4(NG$%3QG$V'&N-3MG)'4]

  To decode the message, your fleet commander enters the keyword "HONDA" and the encoded text. Secret Agent prints out the original message.

HOW IT WORKS

ATTACK PEARL HARBOR AT DAWN!
HONDAHONDAHONDAHONDAHONDAHON

As you see in the above example, the secret keyword is written repeatedly beneath the characters of the message.
  Essentially, Secret Agent takes the ATASCIL number value of a character in the message, adds the ATASCII number value of the next character of the keyword, and prints the ATASCII letter or symbol that matches the resulting total number.

USING THE PROGRAM
Type in Secret Agent, check it with TYPO II, and SAVE a back-up copy. Then RUN it. Secret Agent is menu driven, so you have a clear choice of options at every step. Learning to use the program should only take a few minutes.
  Correct errors as you enter your message with the [DELETE] key End your message by pressing [RETURN]. Notice that the screen automatically supplies square brackets [] to mark off each end of your message. Happy secret coding!

John Smith has a fitting name for a cryptographer. Mr. "Smith" claims to live in Plymouth, Michigan.

Program Listing......AGENT.BAS Download