Exercise A: Peer-to-Peer Chat System

In this exercise, you will implement a simple peer-to-peer network that functions as a distributed chat room. The key features include:

1. Command Line Interface: The chat client runs as a command-line program.
2. Peer Connection: Upon startup, the client requests the IP address and port of an existing peer. If the peer is not found, it starts its own network.
3. Client Details: The client prints its IP address and port for incoming connections.
4. Messaging: The client prompts the user for text strings. When a string is typed, it is broadcast to all connected clients.
5. Message Handling: The system ensures that messages are printed at all clients without revealing the sender's information.

Exercise B: Distributed Ledger

This exercise extends the previous chat system into a distributed ledger with the following features:

1. Ledger Management: Each client maintains a ledger that tracks accounts and balances.
2. Transactions: Clients can make transactions, and all peers update their ledgers accordingly.
3. Eventual Consistency: The system ensures that if all clients stop sending transactions, all ledgers will eventually converge to the same state.
4. Peer Connections: Clients connect to a list of peers and forward transactions to maintain ledger consistency.

Exercise C: Signed Transactions

Enhance the ledger system with signed transactions:

1. Signed Transactions: Transactions are now signed with RSA keys, ensuring only account owners can authorize transactions.
2. Validation: Transactions are validated based on their signature and non-negative amounts.
3. RSA Integration: Encode and decode RSA public keys for transaction processing.

Exercise D: Total Order with Sequencer

Modify the system to achieve total order for transactions:

1. Sequencer Role: A designated sequencer establishes the order of transactions.
2. Block Creation: The sequencer creates blocks containing transaction IDs and signs them.
3. Order Enforcement: Clients process transactions based on the sequencer's block order.

Exercise E: Proof-of-Stake Blockchain

Implement a proof-of-stake based blockchain with total order:

1. Genesis Block: Includes special public keys with initial balances.
2. Proof-of-Stake: A tree-based blockchain where block creation is based on the stake (account balance).
3. Transaction Fees: Implement transaction fees and rewards for block creators.
4. Testing: Validate the system's performance, including handling invalid transactions, rollbacks, and resistance to malicious peers.