Sending RSA encrypted message - From iOS device to Python socket server (Raspberry Pi Part)

Secure Data Transmission: iOS device (Swift) -> Raspberry Pi (Python)

Secure communication between a mobile device client and a server is important. This tutorial selects a Raspberry Pi as the server and uses an iPhone simulator as the client. The communication procedure is as below:

1. Server generates an RSA private / public key pair and sends the public key to iPhone
2. iPhone encrypts a message using the public key provided by server and sends the encrypted message to server
3. Server decrypts the encrypted message from iPhone using the private key

This tutorial is derived from the basic communication between an iPhone and a Python socket server built on a Raspberry Pi without encryption:

Connect an iPhone to a Simple Python Socket Server (Raspberry Pi Part) (iOS Part)

For an overview on client-server communications, see this:

Communication between iOS device (Client) and Raspberry Pi (Server)

Raspberry Pi Part

Raspberry Pi 2 Model B is used. The Python version used is 2.7.3. Check the Python version with the python -V command.

1. Install Python-Crypto.

sudo apt-get install python-crypto

2. Use sudo nano server.py command to edit a python file as below:

import socket

from Crypto.PublicKey import RSA

from Crypto import Random

#Generate private key and public key

random_generator = Random.new().read

private_key = RSA.generate(1024, random_generator)

public_key = private_key.publickey()

#Declartion

mysocket = socket.socket()

host = socket.gethostbyname(socket.getfqdn())

port = xxxx

encrypt_str = "encrypted_message="

if host == "127.0.1.1":

    import commands

    host = commands.getoutput("hostname -I")

print "host = " + host

#Prevent socket.error: [Errno 98] Address already in use

mysocket.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)

mysocket.bind((host, port))

mysocket.listen(5)

c, addr = mysocket.accept()

while True:

    #Wait until data is received.

    data = c.recv(1024)

    data = data.replace("\r\n", '') #remove new line character

    if data == "Client: OK":

        c.send("public_key=" + public_key.exportKey() + "\n")

        print "public key sent"

    elif encrypt_str in data:

        #remove encrypt_str

        data = data.replace(encrypt_str, '')

        #decrypt

        decrypted = private_key.decrypt(data)

        #remove padding

        #See Link: How to decrypt an RSA encrypted file in Python

        if len(decrypted) > 0 and decrypted[0] == '\x02':

            pos = decrypted.find('\x00')

            if pos > 0:

                c.send("Server: OK")

                message = decrypted[pos+1:]

                print message

    elif data == "Quit": break

#Server to stop

c.send("Server stopped\n")

print "Server stopped"

c.close()

iOS Part

Write an iOS app in Swift. See the client version of this post:

Sending RSA encrypted message - From iOS device to Python socket server (iOS Part)

Result

Run both the socket server on Raspberry Pi and iOS simulator on Mac. Press the four app buttons from top to bottom. iPhone sends "Secret message from iPhone!!" to Raspberry Pi:

Reference:

How to decrypt an RSA encrypted file in Python

Go back to Communication between iOS device (Client) and Raspberry Pi (Server)