wait_for_invite.py

#!/usr/bin/env python3
#wait_for_invite.py

import os, sys, getopt
from netsim.netinterface import network_interface
from Crypto.Signature import PKCS1_PSS
from Crypto.Cipher import PKCS1_OAEP
from Crypto.Hash import SHA256
from Crypto.PublicKey import RSA
from datetime import datetime

'''
    Time = 17 bytes
    Cipher = 128 bytes (content = 1 byte (ID) and 16 bytes (public key))
    Signature = length varies, index at i=145 until the end
'''
'''
try:
    opts, args = getopt.getopt(sys.argv[1:], shortopts='hi:s:', longopts=['help', 'inviter=', 'self='])
except getopt.GetoptError:
    print('Usage: python wait_for_invite.py -i <inviter address> -s <self address>')
    sys.exit(1)

if len(opts) != 2:
     print('Usage: python wait_for_invite.py -i <inviter address> -s <self address>')
     sys.exit(1)

for opt, arg in opts:
    if opt == '-h' or opt == '--help':
        print('Usage: python wait_for_invite.py -i <inviter address> -s <self address>')
        sys.exit(0)
    elif opt == '-i' or opt == '--inviter':
        INVITER_ID = arg
    elif opt == '-s' or opt == '--self':
        OWN_ADDR = arg
'''
def receive_invite(netif, OWN_ADDR, password):

    # import private key of invitee(self) for RSA
    prikfile = open("setup/%s-key.pem"%OWN_ADDR,'r')
    prikeystr = prikfile.read()
    prikfile.close()
    prikey = RSA.import_key(prikeystr,passphrase = password)

    #NET_PATH = './netsim/network/'
    print('Main loop started...')
    while True:
        status, msg = netif.receive_msg(blocking=True)
        timestamp = msg[:17]
        ciphertext = msg[17:145]
        signature = msg[145:]
        print('Verifying time stamp...')
        current_time = datetime.now()
        current_timestamp = datetime.timestamp(current_time)
        print("Current timestamp: " + str(current_timestamp))
        print("Received timestamp: " + timestamp.decode('utf-8'))
        if (current_timestamp - float(timestamp) <= 10): # verify time stamp
            print('Time stamp verified')
            cipher = PKCS1_OAEP.new(prikey)
            print('Decryption started...')
            try:
                plaintext = cipher.decrypt(ciphertext)
                print('Decryption success.')
                print('Group ID is ' + (plaintext[1:2]).decode('utf-8'))
                print('Group key is ' + str(plaintext[2:]))
                print('Verifying signature...')
                
                INVITER_ID = plaintext[0:1].decode('utf-8')
                # RSA PKCS1 PSS SIGNATURE
                # import the public key of INVITER_ID
                pubkeystr = ''
                with open('setup/table%s.txt'%OWN_ADDR) as f:
                    kfile = f.read()
                pubkeys = kfile.split("member:")
                pubkeys.pop(0)
                for k in pubkeys:
                    if k[0] == INVITER_ID:
                        pubkeystr = k.split("key:")[1]
                if(pubkeystr == ''):
                    print('No public key string read!')
                    sys.exit(1)
                
                msg_to_be_signed = OWN_ADDR.encode('utf-8') + timestamp + ciphertext
                h = SHA256.new()
                h.update(msg_to_be_signed)
                pubkey = RSA.import_key(pubkeystr)
                verifier = PKCS1_PSS.new(pubkey)
                if verifier.verify(h, signature):
                    print('Signature verified.')
                    return(plaintext[2:])
                else:
                    print('Signature is incorrect!')
                    return
            except ValueError:
                print('Decryption failed. This may be someone else\'s invitation.')
    
        else:
            print('The timestamp has expired.')
            return