################ CSC 15 Lab 9: Interactive Descramble ###################

# This file contains functions provided by the professor to students.
# Place this program in the same directory as your program, and import with
# from scrambase import *
# DO NOT EDIT THIS FILE, JUST INCLUDE IT IN YOURS.

# This file already contains files that reads three permutations, LP, PI
# and BP from a file named "key1.txt") (make sure this file is also in the
# same directory).  
### LP is a permutation of length 128. It permutes the ascci char set
### so that each letter is mapped to another letter.
### PI is a permutation of length 64. It should be used to permute the
### position of the characters in a string.
### BP is a permutation of length 7. It represents a bitwise permutation
### of an 8-bit non-negative value (first bit stays 0).

# Study the function "download" below to learn how it is to be used.
# This function allows you to send and receive a message, at varying
# levels of encryption, interactively with the professor's server over
# the network.  

# The professor's server is running at 147.4.180.39, port 10024.  However,
# multiple servers may be made available on other ports

### This assignment must be completed on a non-wifi computer on campus
### as Hofstra's wireless routers block the ports that we need.

### Note that the download function takes a parameter indicating the
### encryption level of the message.  
# level 0 is plain text
# level 1 scrambles the positions of the chars (using PI and its inverse)
# level 2 is level 1 plus scrambling of ascii char set (using LP)
# level 3 is level 2 plus bit-wise scrambling of each 8-bit value. LP is
# applied before BP when scrambling.
### Note that the 'message' argument to download need to be encrypted at
### the level indicated.  You will receive an crypted message from the
### professor encrypted at the same level, which you will need to decrypt.
### Optionally, you may write what you received to a file using the 
### writefile function included here.

# Write a function that interactively take info from you, scramble,
# then call download to interact with the professor.  Be nice to the
# professor, who have already provided you enough code for level 1
# encryption (see homepage).

### Please pad your strings with blank spaces for easy reading.


from string import join  # join(['a','b','c'],"") gives "abc"
from socket import *
# range(0,n) gives id permutation from 0 to n-1

# returns inverse permutation of P: Q[P[i]] = i
def inverse(P):
   Q = [0]*len(P)
   i = 0
   while i< len(P):
     Q[P[i]] = i
     i += 1
   #
   return Q
# inverse permutation of P

### This function takes a filename (such as "key1.txt"), reads it and
### returns a triple (LP,PI,BP):
### which are interpreted as follows:
### LP is a permutation of length 128. It permutes the ascci char set
### so that each letter is mapped to another letter.
### PI is a permutation of length 64. It should be used to permute the
### position of the characters in a string.
### BP is a permutation of length 7. It represents a bitwise permutation
### of an 8-bit non-negative value (first bit stays 0).
def readkey(filename):
  fd = open(filename,"r")
  n = int(fd.readline())
  P = [0]*n
  i = 0
  while i<n:  # alternatively, fd.readline() returns "" at EOF.
    P[i] = int(fd.readline())
    i += 1
  # while
  n = int(fd.readline())
  K = [0]*n
  i = 0
  while i<n:  # alternatively, fd.readline() returns "" at EOF.
    K[i] = int(fd.readline())
    i += 1
  # while
  n = int(fd.readline())
  B = [0]*n
  i = 0
  while i<n:  # alternatively, fd.readline() returns "" at EOF.
    B[i] = int(fd.readline())
    i += 1
  # while
  fd.close()
  return P,K,B
#readperm

#### read permutations from file
(LP,PI,BP) = readkey("key1.txt")
PL = inverse(LP)
IP = inverse(PI)
PB = inverse(BP)
#print LP
#print IP 
#print PB

#### functions to read/write strings from/to file
def readfile(filename):
    fd = open(filename,"r");
    F = fd.read();   # reads entire file into a string
    fd.close()
    return F   # returns string read
#readfile

# write string S to (string) file
def writefile(S,filename):
    fd = open(filename,"w")
    fd.write(S)
    fd.close()  # nothing is returned
#writefile


#############
# Download info from tcp/ip server at serverip:serverport; returns string.
# Note the serverip is a STRING and serverport is a number.
# message is the string that you want to send to the professor, encrypted
# at level elevel.  
# level 0 is plain text
# level 1 scrambles the positions of the chars
# level 2 is level 1 plus scrambling of ascii char set
# level 3 is level 2 plus bit-wise scrambling of each bit.  For this level,
# the LP permutation is applied before BP when scrambling
# Note that unless elevel=0, message should not be in plain text.
def download(serverip,serverport,message,elevel):
    cfd = socket(AF_INET, SOCK_STREAM)  # create comm socket
    cfd.connect((serverip,serverport)) # connect to server
    if (elevel<0 or elevel>3): elevel=0  # force to be plain text
    if len(message)>=1024: message = message[:1023]
    el = chr(elevel+48)
    cfd.send(el)  # send level indicator
    cfd.send(message);    # send message to server
    s = ""  # string to be assembled
    r = "abc" # something not empty
    while r:   # this means while r is not "null"
        r = cfd.recv(1024)  # read up to 1K
        if (r): s = s+r
    # read loop
    cfd.close()  # close socket
    return s  # return string read from socket (could be encrypted)
##download


### sample usage:
# s = download("147.4.180.39",10024,"Give me a D!",0)
# s = download("147.4.180.39",10024,scramble1("Give me a C!"),1)
# s = download("147.4.180.39",10024,scramble2("Give me a B!"),2)
# s = download("147.4.180.39",10024,scramble3("Give me an A!"),3)
# print s
# This assumes that scramble1/2/3 are your scramble functions.