: You are required to implement a server program that responds to both TCP and UDP requests from the corresponding clients. The service provided by the server is simply a substitute cipher/cryptosystem. The cipher replaces one character to another based on some key. The input message (plaintext) can be of any size but composed only of small-letter (abcdefghijklmnopqrstuvwxyz). The output (ciphertext) has the same size and composed also of small-letter characters. The key is limited to 7 characters (also small-letter). You need to treat each digit as a number according to its position in the alphabet. For example, a=0, b=1, …,z=26. To encrypt a message, you add a plaintext character with the corresponding key character (mod 26). The key might be repeated to match the length of the plaintext message. In the decryption, you subtract the corresponding key character from the ciphertext character (mod 26). Again the key might be repeated as necessary. For example, if the key is “nesdept” the process goes as follows: Plaintext: hellostudents Key: nesdeptnesdept Ciphertext: uidoshmhhwqxh In the decryption, the reverse is performed so you get the original massage. The server should wait for requests on the same port for both TCP and UDP requests. T

Computer Networking: A Top-Down Approach (7th Edition)

7th Edition

ISBN:9780133594140

Author:James Kurose, Keith Ross

Publisher:James Kurose, Keith Ross

Chapter1: Computer Networks And The Internet

Section: Chapter Questions

Problem R1RQ: What is the difference between a host and an end system? List several different types of end...

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Description: You are required to implement a server program that responds to both TCP and UDP requests from the corresponding clients. The service provided by the server is simply a substitute cipher/cryptosystem. The cipher replaces one character to another based on some key. The input message (plaintext) can be of any size but composed only of small-letter (abcdefghijklmnopqrstuvwxyz). The output (ciphertext) has the same size and composed also of small-letter characters. The key is limited to 7 characters (also small-letter). You need to treat each digit as a number according to its position in the alphabet. For example, a=0, b=1, …,z=26. To encrypt a message, you add a plaintext character with the corresponding key character (mod 26). The key might be repeated to match the length of the plaintext message. In the decryption, you subtract the corresponding key character from the ciphertext character (mod 26). Again the key might be repeated as necessary. For example, if the key is “nesdept” the process goes as follows: Plaintext: hellostudents Key: nesdeptnesdept Ciphertext: uidoshmhhwqxh In the decryption, the reverse is performed so you get the original massage. The server should wait for requests on the same port for both TCP and UDP requests. The TCP part MUST be concurrent. However, the UDP part must be iterative. Furthermore, you are requested to use host and service names in you code, rather that the IP and port numbers. That is, you need to edit some configuration files (see lecture recordings) and add necessary lines to map between your server local IP address and some hostname, and also to map between your server port number and some service name. For this assignment, the server hostname is nes416_crypto_server and the service name is nes416_port. The client part (TCP or UDP), will display the following menu to the user to select from: 1. Encrypt a message 2. Decrypt a message 3. Exit 4. Listing files in the current directory on the server If the user selects 1, the encryption must be implemented by the client. The client asks the user to enter a plaintext message (NULL terminated) and a key. Then it encrypts the message and sends it to the server. The server, which implements the decryption, reads the encrypted message, asks the user to enter the key, then sends the plaintext message to the client. Then, the client prints the received message on standard output together with the IP address and port number of the server. If the user selects 2, the decryption must be implemented by the client. The client asks the user to enter a ciphertext message (NULL terminated) and a key. Then it decrypts the message and sends it to the server. The server, which implements the encryption in this case, reads the decrypted message, asks the user to enter the key, then sends the corresponding ciphertext message to the client. Then, the client prints the received message on standard output together with the IP address and port number of the server.The connection between your client and server should stay open, so that the client can repeat the operation again. You should also add a logout or stop type of a command so that the client can tell the server that it is finished and the session should end. For example, if the user enters --, the client and server program terminates. Note that the server displays the IP address and port number of each client request Output Sample: For example, running the code should produce something similar to this output: Client> Enter a msg: hellostudents Enter a key= nesdept Sent Encrypted msg: uidoshmhhwqxh Received plaintext msg: hellostudents from the server(print the IP address and port number of the server) Enter a msg: -- Exiting...thank you Server> waiting for client’s request Received ciphertext uidoshmhhwqxh from client:(print the IP address and port number of the client) Enter Key: nesdept Sent hellostudents to the client Waiting for clients request Received -- from client:(print the IP address and port number of the client) Exiting…

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