Introduction

Purpose:

The purpose of this program is to encrypt and decrypt data primarily for transmission over the internet but it can also be used on the hard drive, floppy disks etc

The principle of the encryption is as follows:

The text is read into the program either from file or by the user. An array of random characters is created, the array is the length of the inputted text ie if the word “the” was to be encrypted 3 random characters would be created and put into an array. The program then looks at the first character of the inputted text and the first item in the array of random characters and adds their ASCII values together this is then done for the second character and so-on. The program then joins the shifted inputted text with the array of random characters and the encryption is complete.

If a key is entered by the user:

Once the array of random characters has been generated the key that the user typed in is placed in an array. The program looks at the first cell of the random characters and the first cell of the users key and adds the two ASCII values together this is then done for the second character and so-on. If the users key is shorter than the array of random characters then once the program has finished using all of the character in the array it starts back at the beginning of the users key.

e.g.

ABCD is the inputted text

1234 is the random generated array

56 is the key entered by the user

The random generated array is changed as follows.

1 becomes 6

first cell of random characters is added to the first digit in the users key.

2 becomes 8

second cell of random characters is added to the second digit in the users key.

3 becomes 8

There are no more characters left in the users key so it go back to the first character in the key and adds the first character of the users key to the third cell of the random characters

4 becomes 10

The second character of the users key is added to the fourth cell of the random characters.

The principle of the decryption is as follows:

The text is inputted into the program either from file or inputted manually by the user. This program separates the array of random characters from the shifted text, this is done by taking every second character out of the text. The program then looks at the first character of the shifted text and then the first cell of the array of random numbers and subtract the ASCII value of the array of random numbers from the shifted text. This is then done for the second character and so-on.

If a key was used:

The random characters are extracted from the encrypted data as described above and placed in an array and the user enters the key. The first cell of the array of random characters has the ASCII value of the first character in the users key subtracted from it, this is then done for the second cell and so-on. If the user key is shorter than the array of random characters then the method as described in the encryption method is used to go back to the beginning of the users key when all of its characters have been used.

Start-up Screen

This is the start-up screen and from here you are able to open the encryption window, open the decryption window and exit the program.

Encrypting/ Decrypting

From File:

To encrypt/ decrypt a file it must be a text document (*.txt), have its address specified and this button must be selected. The address can be specified in one of two ways.

1. Typing in the address manually here

2. Search for the file by looking at the text files on your computer by clicking here

Searching for a file:

This allows you to select where on your computer you can look for text files.

To change the drive you are looking at simply click here and select the desired drive.

To change the directory select the desired directory here and to select a text file select it from this box

Saving:

Once the file has been encrypted or decrypted the text will appear in the text box and you will have the option to save what is in the text box to the file the original text came from.

WARNING: If you press the save button and press yes at the prompt when the text box is empty the file will become empty.

By Typing

It is also possible to type in text to be encrypted/ decrypted and not have the text come from a file. To type in text press these two buttons, the one on the right first.

Typing in text

To type/ paste in text simply type here and press OK when finished.

The Key

A key can be used to add extra security to the encryption. The program is still relatively secure when a key is not used however if a document is of importance the use of a key should be considered. Simply select “yes” here type the key you desire here before pressing encrypt or decrypt.

Errors and Trouble Shooting

Common errors

A message “An error occurred during this operation, please ensure a correct file path was entered”.

This message occurs during the encryption, decryption or saving process. The most common cause of this error is if no file path was entered or an incorrect one was entered. To resolve the problem simply press ok and type or search for the correct file path.

The text did not decrypt

The most common reason for this occurring is if the key that was used for encrypting was not the same one that was used decrypting. To resolve this problem ensure that the correct key is entered.

The problem could also have occurred if not all of the text was inputted, if the text was manually pasted or typed ensure that there were no characters left out, this can include spaces at the end of the encrypted data.

If problem persists contact developer.

When the text is encrypted there are large spaces or empty lines

This is expected within the encrypted text and is only part of the encryption.

I don’t know how to run the program

Simply access your CD ROM drive and click encryption.exe

I can’t run the help file

Ensure that the help disk is in a drive and that your computer supports Microsoft word.