add complete solution

This commit is contained in:
Tiziano Zito 2024-08-19 12:27:42 +02:00
parent 91f237edf2
commit 7e2039734e
2 changed files with 106 additions and 0 deletions

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.gitignore vendored Normal file
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pwdb.json

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