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Feature
REALSecure
Random Number Encryption
Issue: 5.4 (May/June 2007)
Author: JC Cruz
Article Description: No description available.
Article Length (in bytes): 22,434
Starting Page Number: 21
RBD Number: 5411
Resource File(s):
5411.zip Updated: Saturday, July 28, 2007 at 12:08 AM
Related Web Link(s):
http://en.wikipedia.org/wiki/Linear_feedback_shift_register
http://en.wikipedia.org/wiki/Cipher
http://en.wikipedia.org/wiki/Stream_cipher
Known Limitations: None
Excerpt of article text...
Today, we will learn how to use a random number generator as the basis of a cipher system. We will also learn more about the LFSR generator, and how to make it non-linear. We will then build a basic Vernam cipher using the modified LFSR generator and REALbasic.
A Brief Primer on Cryptography
The field of cryptography is the study of cipher systems. A cipher system allows the secure exchange of data in the presence of adversaries. In a well-designed system, only the intended receiver will be able to read the secured data.
Figure 1 shows a basic cipher system in action. The sender first enters the original data, or plaintext, into a cipher function. She then enters a second piece of data, the key, into the same function. The cipher function combines the two data streams and outputs the results as the ciphertext. This step is known as encryption.
The sender then sends the ciphertext to the receiver. The receiver feeds the ciphertext into the same cipher function. He also enters a key into the function. The cipher function combines the ciphertext and key, and gives the original plaintext as a result (Figure 2). This step is known as decryption.
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Article copyrighted by REALbasic Developer magazine. All rights reserved.
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