What is fundamental difference between Process and Threads? How are the threads useful to establish concurrent socket communication? How do you perform secure communication using RSA? Explain with example.

Process vs Threads:

Basis	Process	Thread
Meaning	Independent program in execution (own memory)	Lightweight unit inside a process (shares memory)
Memory	Separate address space	Shared code/data of parent process
Cost	Heavy to create/switch	Light, fast switch
Example	Word and Browser are two processes	Word's spell-check + typing are threads

Threads for concurrent socket communication: A server must serve many clients at once. Single-threaded server handles one client, others wait. Multi-threaded server creates one thread per client socket — e.g. police record server: thread-1 handles Kathmandu query, thread-2 handles Surkhet query simultaneously on same port, sharing the database connection pool. Non-blocking I/O + thread pool prevents one slow client blocking others.

Secure communication with RSA (example): RSA is asymmetric: public key encrypts, private key decrypts.

1. Receiver (server) generates key pair, shares public key openly, keeps private key secret.
2. Sender encrypts message: cipher = message^e mod n using receiver's public key.
3. Only receiver decrypts with private key. Eavesdropper with only public key cannot reverse it feasibly.

Example: ASI exam server publishes public key; constable encrypts FIR text with it; only server's private key opens it. In practice RSA exchanges a session key, then fast AES encrypts bulk data (hybrid) with digital signature for authenticity.