Encryption Requirements of the Exercise I

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Objectives Security is a critical part of electronic commerce systems, and public key cryptography is widely used to secure online transactions. Though most likely you will not be asked to implement a security scheme while working for the industry, public key cryptography is fundamental knowledge that an IT worker needs to know, and this implementation will help you understand how the knowledge is put to work.

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The Problem
This slide gives programming requirements to implement the example in Crypto Primer (Understanding encryption, public/private key, signatures and certificates). In the real world, there should have two servers performing encryption and decryption, respectively:

• (Encryption) A local server encrypts the plaintext and generates the ciphertext from the plaintext.
• (Decryption) A remote server decrypts the ciphertext and converts it back to the plaintext.

Since there is only one server available at the CEM, this slide will simulate both the encryption and decryption by using one server including two applications:

• (Decryption) This application performs the following tasks in the beginning:
  
  
  1. generating a pair of a public key and a private key, and
  2. sending the public key to the encryption application.


• (Encryption) It performs the following operations:
  
  
  1. receiving a public key from the decryption application,
  2. encrypting the password by using the public key, and
  3. sending the ciphertext to the decryption application.


• (Decryption) The decryption performs the following tasks subsequently:
  
  
  1. receiving the ciphertext from the encryption application, and
  2. decrypting the ciphertext and converting it back to the password.

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Requirements
The following requirements need to be followed:

• Two different requirements are
  
  
  • The undergraduate students could use any encryption method as long as it works and the ciphertext can not be easily decrypted. Of course, they may use the method used by the graduate students.
  • The graduate students must follow the method given by the example. No other methods can be used for the sake of fairness. May convert the passwords character by character which may simplify the encryption.


• Various passwords will be converted to different ciphertext during grading.


• The one correct password has to be submitted with your emails, and only it will be able to display the source code.


• Only ciphertext, no plain passwords, will be sent to the (decryption) server. This feature will be checked by studying the source code by the instructor.


• The source code to be displayed includes all code (including PHP, Java, Perl, JavaScript, HTML, CSS, and whatever languages) used by your exercise. The source code will be studied carefully for any suspected plagiarism. Besides, the exercise is suspicious if the displayed code is substantially different from the displayed code.


• The system can be reset, which is to clear all data stored in the files or database, so the instructor can test the system by using only his own test data. That is the system has to include a button such as “Clear system” in the system entry page.

The following comments are for your reference:

• Euclidian algorithm may be used to find a private key. The page modular multiplicative inverse from GeeksforGeeks may be used.


• BigInteger in PHP may be used for calculation. The instructor will try to enter small numbers for input.

Another similar paper can be found at Cryptography: A modern use for modular arithmetic. An example of the user interface is shown next, and its source code can be found from here.