81.

Learn Encryption Techniques with BASIC and C++
(Publisher: Wordware Publishing, Inc.)
Author(s): Gil Held
ISBN: 1556225989
Publication Date: 10/01/98

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The DECIPHER.EXE Program

The program DECIPHER.BAS is provided in both source and executable versions on the CD-ROM accompanying this book. Similar to the ENCIPHER.EXE program, the program DECIPHER.EXE operates through the use of three screens. The execution of the program DECIPHER.EXE is illustrated in Figures 7.4 through 7.6.

To illustrate the use of the deciphering program I will use the program to operate upon the previously enciphered message contained on the file CIPHERTX.DAT. Figure 7.4 illustrates the entry of the same “secret” code that was used to encipher our previously created plaintext message.


Figure 7.4  The first screen displayed upon execution of DECIPHER.EXE.

Once your “secret” code is entered, the program displays a second screen which, similar to ENCIPHER.EXE, enables you to assign filenames for storing the plaintext and enciphered messages and select keyboard or file input (Figure 7.5). In this example, the default filenames were accepted and once the deciphering operation commenced, an appropriate message was displayed. After the deciphering operation is completed and you press the Return key, the resulting deciphered message is displayed. This is illustrated in Figure 7.6. In comparing the plaintext message in Figure 7.2 to the deciphered message contained in Figure 7.6, you will note they are exactly the same.


Figure 7.5  The second screen displayed upon execution of DECIPHER.EXE.


Figure 7.6  The resulting deciphered message.

The Challenge

In concluding this chapter, an enciphered message is presented in Figure 7.7. Unlike the task faced by most cryptanalysts who do not have access to an enciphering system used to create a message, I have considerably simplified the task of those who may wish to decipher this message. This message was enciphered using the directly executable program ENCIPHER.EXE which is contained on the CD-ROM in the BASIC directory. The enciphered message, which is stored on the file CIPHERTX.DAT on the CD-ROM, can be deciphered using the directly executable program DECIPHER.EXE, which is also contained on the CD-ROM. To facilitate your effort, unlike the original version of this book, this new edition contains both source and executable versions of the programs ENCIPHER and DECIPHER.


Figure 7.7  The “challenge” message.

Providing the deciphering program may simplify the task of deciphering the message. You can consider using a trial-and-error approach by using different “secret” codes in an attempt to decipher the message. As you cycle through various combinations of “secret” codes, one of the points raised a number of times in this book will become apparent—the program provides a level of privacy for electronic transmission that will deter the casual observer of a message from understanding the contents of the message.

The reason for originally providing only directly executable copies of the two programs whose use was described in this chapter was to hide the technique employed to use the “secret” code used by the enciphering program to generate a random number sequence. Although I originally left the door unlocked, I purposely decided not to turn on the lights!

In a future edition of this book, I anticipate extending the coverage of topics to codebreaking. Thus, if you feel you are successful in deciphering the message illustrated in Figure 7.7 and contained on the file SECRET.MSG, please send a description of the approach you used to decipher the message as well as the deciphered message to me via e-mail at 235-8068@mcimail.com.

I would like to consider describing techniques used by you to decipher the message illustrated in Figure 7.7 or even approaches you took that were not successful. Thus, I welcome all reader comments concerning not only the specific message you are challenged to decipher but all aspects of this book.


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Learn Encryption Techniques with Basic and C++
Learn Encryption Techniques with BASIC and C++
ISBN: 1556225989
EAN: 2147483647
Year: 2005
Pages: 92
Authors: Gil Held

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