updated IS codes

IS/Lab/Lab6/socket_rsa/server.py

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+import socket
+from typing import Tuple
+
+from Crypto.PublicKey import RSA
+from Crypto.Cipher import PKCS1_OAEP
+
+
+def generate_rsa(bits: int = 2048) -> Tuple[RSA.RsaKey, RSA.RsaKey]:
+    key = RSA.generate(bits)
+    return key.publickey(), key
+
+
+def main() -> None:
+    host = "127.0.0.1"
+    port = 5003
+
+    pub, priv = generate_rsa(2048)
+    pub_pem = pub.export_key()
+
+    with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as srv:
+        srv.bind((host, port))
+        srv.listen(1)
+        conn, _ = srv.accept()
+        with conn:
+            # Send server public key
+            conn.sendall(len(pub_pem).to_bytes(4, "big") + pub_pem)
+
+            # Receive client's encrypted message
+            clen = int.from_bytes(conn.recv(4), "big")
+            ctext = conn.recv(clen)
+
+            cipher = PKCS1_OAEP.new(priv)
+            msg = cipher.decrypt(ctext)
+            # Respond: encrypt reply with same public (client will not be able to decrypt without its private),
+            # so just echo plaintext length as acknowledgement for demo.
+            reply = f"received:{len(msg)}".encode()
+            conn.sendall(len(reply).to_bytes(4, "big") + reply)
+
+
+if __name__ == "__main__":
+    main()
+
+