local vs global variables Python

Question

I am new to programming and am wondering if this is possible. I am trying to create a password protected script, where the password is entered once and then required to progress the script the next time the script is opened. I am storing and encrypting the password in a file, and then checking to see if the file exists the next time the script is opened. The problem I am running into is checking to see if the passwords match, since the original password is in a function as a local variable.

def createFile():
 pw = input('Enter Password: ')
 pw2 = input('ReType Password: ')
 if pw == pw2: 
 newPw = encrypt(pw, 10) #encodes the string with a key in a seperate encrypt function
 pwFile = open('PW.txt', 'a')
 pwFile.write(newPw)
 pwFile.close()
 else:
 print('The passwords do not match')
 createFile()
if os.path.isfile('PW.txt'):
 print('File exists')
 pwCheck = input('What is the password? ')
 #I can not check pwCheck == pw since pw is a local var.
 #progression of script here
else:
 createFile()

I know that it is considered bad for to make a local variable global. Is there a way to restructure what I have so far to make this work? As I wrote this, I think I may have came up with a possible solution but I do not have time to test it now. Do I run the same encrypt function with the same key for pwCheck and then check if it is == to the first line of PW.txt? Is that correct and/or are there other solutions?

Thank you.

Using Windows, Python 3.4

• Claudiu: You have to read the existing password from the file, decrypt it, and check it against pwCheck
• jonrsharpe: Note that it's wiser to store the hash of the password, then compare the hash of the user input to what is in the file.

Answer 1

Instead of "encrypt", perhaps use a 1-way hash.. Then, you can hash the subsequently entered password and check it versus the hash stored in the file... Something like:

def createFile():
 pw = input('Enter Password: ')
 pw2 = input('ReType Password: ')
 if pw == pw2: 
 newPw = sha.new(pw).digest
 pwFile = open('PW.txt', 'a')
 pwFile.write(newPw)
 pwFile.close()
 else:
 print('The passwords do not match')
 createFile()
if os.path.isfile('PW.txt'):
 print('File exists')
 pwCheck = input('What is the password? ')
 previous = open('PW.txt', 'r')
 prevPass = previous.read()
 hashed = sha.new(pwCheck).digest()
 if (hashed==prevPass):
 #progression of script here
else:
 createFile()

Answer 2

I really hope that this is just an exercise, because if you care about security, you should be using some other authentication mechanism to gate access. Most obviously, unix permissions, and sudo to gate access.

Assuming it is an exercise only, simply have a function which checks the input against the file. Something like:

def doAuth():
 isAuthed = getPassInput() == getPassFromFile()
 if isAuthed:
 return True
 else:
 raise HellNoException("Passwords differ")