Computer-Networks

Various projects implemented in the "Computer Networks" course:

• TCP-Server: a TCP client and server in C
  • The protocol between the client and server will use four types of messages: Initialization, Acknowledgement, HashRequest, and HashResponse. The client starts by sending an Initialization message to the server, which informs the server of the number of hashing requests that the client will make (denoted by the variable N). Afterwards, the client sends N HashRequest messages to the server, where each HashRequest contains the data segment to be hashed. The server responds to the Initialization message with an Acknowledgement, which informs the client of the total length of the response. The server responds to each HashRequest with a HashResponse that contains the hash of the corresponding data.
• UDP-Server: UDP client and server to run a simplified version of NTP (Network Time Protocol) in C
  • The protocol implemented resembles that of NTP and will use two types of messages: TimeRequests and TimeResponses. In this project, the packet payloads will include the time on the machine when the packet was sent. clock_gettime() was used to get the current time; that function writes the time into a timespec structure containing two 64-bit unsigned integers (the number of seconds and nanoseconds since the start of the epoch). These values will be referred to hereon as the time in seconds and the time in nanoseconds. Unlike the protocol in tcp-server, there is no initialization. The client sends a TimeRequest that contains a sequence number for the request and a timestamp of when it sent the payload. Upon receiving the TimeRequest, the server replies with a TimeResponse that contains the same sequence number and timestamp in the TimeRequest, as well as a timestamp of when the server sends the TimeResponse. The formats of these messages are shown below.
• Chatroom: Reverse engineer a provided chat client chat server to implement a suitable server.
  • In this project, I was provided a chat client and chat server. Clients allow users to communicate with one another by connecting to the server and interacting with it in accordance to an application protocol. Through this protocol, the server allows clients to engage in group chats in chat rooms and send private messages to one another. My task was to reverse engineer the chat server and its protocol and use this information to write a compatible replacement.