James Encryption

#  James programme!
http://gcsecompsci.weebly.com/uploads/3/0/9/3/30931869/2016_unit_1_traditional_scenario.pdf

import random

def mainmenu():
    print("1. Encrypt a message")
    print("2. Decrypt a message")
    print("3. Extended Encryption")
    print("4. exit\n")

def mkoffset():  # makes the offset key
    key = ""
    tot = 0
    for i in range(8):
        seed = random.randint(33,126)
        tot += seed
        ASCIIchar = chr(seed)
        key += ASCIIchar
    print(key)
    offset = (tot//8) - 32
    return offset

def convertoffset(key): #convert offset key
    tot = 0
    for i in range(len(key)):
        ASCIInum = ord(key[i])
        tot += ASCIInum
    offset = (tot//8) - 32
    return offset

def encrypt(text): # encrypt a message
    codedmsg = ""
    for i in range (len(text)):
        if text[i] == " ":
            codedmsg += " "
        elif ord(text[i]) + offst > 126:
            codedmsg += chr(ord(text[i]) + offst - 94)
        else:
            codedmsg += chr(ord(text[i]) + offst)
    return codedmsg

def decrypt(text): # decrypt a message
    decodedmsg = ""
    for i in range(len(text)):
        if text[i] == " ":
            decodedmsg += " "
        elif ord(text[i]) - offsetkey < 33:
            decodedmsg += chr(ord(text[i]) - offsetkey + 94)
        else:
            decodedmsg += chr(ord(text[i]) - offsetkey)
    return decodedmsg

def enhancedencrypt(text): # batch the message into groups of 5's
    codedmsg = ""
    for i in range (len(text)):
        if text[i] == " ":
            pass # ie do nothing, strip the spaces
        elif ord(text[i]) + offst > 126:
            codedmsg += chr(ord(text[i]) + offst - 94)
            if len(codedmsg)%5 == 0 and i != len(text):
                codedmsg += " "
        else:
            codedmsg += chr(ord(text[i]) + offst)
            if len(codedmsg)%5 == 0 and i != len(text):
                codedmsg += " "
    return codedmsg


mainmenu()
option = int(input("Please select your option >> "))

if option == 1:
    filename = input("Please enter the file name to be encrpted, includng file extension >> ")
    file = open(filename,"r")
    fileconts = file.read()
    file.close()
    print(fileconts)
    offst = mkoffset() # generates offset key
    print(offst)
    newmssg = encrypt(fileconts)
    print(newmssg)
    savefilename = input("Please enter the name the encrypted file should be saved as, with extension >> ")
    file = open(savefilename,"w")
    file.write(newmssg)
    file.close()

elif option == 2:
    filename = input("Please enter the file name of the encrypted file, including file extension >> ")
    file = open(filename,"r")
    fileconts = file.read()
    file.close()
    key = input("please enter the 8 digit key >> ")
    offsetkey = (convertoffset(key))
    decodedmessage = decrypt(fileconts)
    print(decodedmessage)

elif option == 3:
    filename = input("Please enter the file name to be encrpted, includng file extension >> ")
    file = open(filename,"r")
    fileconts = file.read()
    file.close()
    print(fileconts)
    offst = mkoffset() # generates offset key
    print(offst)
    newmssg = enhancedencrypt(fileconts)
    print(newmssg)
    savefilename = input("Please enter the name the encrypted file should be saved as, with extension >> ")
    file = open(savefilename,"w")
    file.write(newmssg)
    file.close()

else:
    print("exiting . . ")
    quit