106 lines
3 KiB
Python
106 lines
3 KiB
Python
import getpass
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import json
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import pathlib
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import random
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import string
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import sys
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# name of the file where we store the pw database
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PWDB_FLNAME = pathlib.Path('pwdb.json')
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# list of valid characters for salt (only ASCII letters + digits + punctuation)
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CHARS = string.ascii_letters + string.digits + string.punctuation
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# length of salt
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SALT_LENGTH = 5
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def get_credentials():
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# get input from terminal
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username = input('Enter your username: ')
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# get password using the appropriate module, so that typed characters are not
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# echoed to the terminal
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password = getpass.getpass('Enter your password: ')
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return (username, password)
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def authenticate(username, pass_text, pwdb):
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# get the salt from the database
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salt = pwdb[username][1]
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# calculate hash and compare with stored hash
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return pwhash(pass_text, salt) == pwdb[username][0]
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def add_user(username, pwdb):
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# do not try to add a username twice
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if username in pwdb:
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raise Exception(f'Username already exists [{username}]!')
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else:
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password = getpass.getpass(f'Enter password for {username}: ')
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salt = get_salt()
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pwdb[username] = (pwhash(password,salt), salt)
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return pwdb
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def read_pwdb(pwdb_path):
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# try to read from the database
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# if anything happens, report the error!
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if not pwdb_path.exists():
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initialize_pwdb(pwdb_path)
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try:
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with open(pwdb_path, 'rt') as pwdb_file:
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pwdb = json.load(pwdb_file)
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except json.decoder.JSONDecodeError as exc:
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# this happens when the json data is invalid
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raise Exception(f'Invalid database {pwdb_path}: {exc}')
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except Exception as exc:
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# this is a catch-all condition
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raise Exception(f'Unkown error reading {pwdb_path}: {exc}')
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return pwdb
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def write_pwdb(pwdb, pwdb_path):
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with open(pwdb_path, 'wt') as pwdb_file:
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json.dump(pwdb, pwdb_file)
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def pwhash(pass_text, salt):
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# simple additive hash -> very insecure!
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hash_ = 0
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full_pass_text = pass_text + salt
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for idx, char in enumerate(full_pass_text):
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# use idx as a multiplier, so that shuffling the characters returns a
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# different hash
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hash_ += (idx+1)*ord(char)
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return hash_
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def get_salt():
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salt_chars = random.choices(CHARS, k=SALT_LENGTH)
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return ''.join(salt_chars)
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def initialize_pwdb(pwdb_path):
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write_pwdb({}, pwdb_path)
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def main(pwdb_path):
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# load the password database from file
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pwdb = read_pwdb(pwdb_path)
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# if we are passed an argument, we want to add a new user
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if len(sys.argv) > 1:
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pwdb = add_user(sys.argv[1], pwdb)
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write_pwdb(pwdb, pwdb_path)
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return
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# ask for credentials
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username, password = get_credentials()
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if username not in pwdb:
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print('Wrong username!')
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return
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# try to authenticate
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if authenticate(username, password, pwdb):
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print('Successfully authenticated!')
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else:
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# report wrong password
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print('Wrong password!')
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return
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if __name__ == '__main__':
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main(PWDB_FLNAME)
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