CertAuth.py

from cryptography import x509
from cryptography.hazmat.primitives.asymmetric import padding
from cryptography.hazmat.primitives import hashes
from cryptography.hazmat.backends import default_backend
import argparse
from OpenSSL.crypto import *


def parse():
    parser = argparse.ArgumentParser(description=
                                     "Sample : python3 CertAuth.py cert_bckup.p12 root.crt subject.crt CSE539_Rocks!",
                                     usage="python3 CertAuth.py <path for backup private key> <CA public certificate> "
                                           "<subject public certificate> <password for backup private key>")
    parser.add_argument('arguments', type=str, nargs=4, help="includes file paths and passwords needed for successful "
                                                             "execution")
    args = parser.parse_args()
    return args.arguments


def get_hex(test):
    values = []
    for char in test:
        values.append('{0:02x}'.format(int(char)))
    return "".join(values)


def tasks(arguments):

    PRIVATE_KEY_FILE_PATH = arguments[0]
    ROOT_CERT_FILE_PATH = arguments[1]
    SUBJECT_CERT_FILE_PATH = arguments[2]
    PRIVATE_KEY_PASSWORD = arguments[3]

    # load the certificate files
    # using 'with open(...) as file' closes the file automatically
    with open(SUBJECT_CERT_FILE_PATH, "rb") as file: 
        crt_data = file.read()
        subject_certificate = load_certificate(FILETYPE_PEM, crt_data)
        subject_certificate_x509 = x509.load_pem_x509_certificate(crt_data, default_backend())
    
    with open(ROOT_CERT_FILE_PATH, "rb") as file:
        root_crt_data = file.read()
        root_certificate = load_certificate(FILETYPE_PEM, root_crt_data)
        root_certificate_x509 = x509.load_pem_x509_certificate(root_crt_data, default_backend())
    
    with open(PRIVATE_KEY_FILE_PATH, "rb") as file:
        subject_pkcs12 = load_pkcs12(file.read(), PRIVATE_KEY_PASSWORD)
        
    # task 1

    root_cert_store = X509Store()
    root_cert_store.add_cert(root_certificate)
    root_store_context = X509StoreContext(root_cert_store, subject_certificate)

    try:
        root_store_context.verify_certificate()
    except X509StoreContextError:
        print(False)
    else:
        print(True)

    # task 2
    print()
    print(subject_certificate.get_subject().CN)
    print()
    print(subject_certificate.get_issuer().CN)
    print()
    print(subject_certificate.get_serial_number())
    print()
    print(subject_certificate_x509.signature_hash_algorithm.name)
    print()
    print(subject_certificate.get_notBefore().decode())
    print()
    print(subject_certificate.get_notAfter().decode())

    # task 3
    subject_numbers = subject_certificate_x509.public_key().public_numbers()
    subject_private_numbers = subject_pkcs12.get_privatekey().to_cryptography_key().private_numbers()
    print()
    print(subject_numbers.n)
    print()
    print(subject_numbers.e)
    print()
    print(subject_private_numbers.d)
    
    # task 4
    root_numbers = root_certificate_x509.public_key().public_numbers()
    print()
    print(root_numbers.n)
    print()
    print(root_numbers.e)

    # task 5 - Signature
    subject_x509_data = open(SUBJECT_CERT_FILE_PATH, "rb").read()
    subject_x509 = x509.load_pem_x509_certificate(subject_x509_data, default_backend())
    signature = subject_x509.signature
    print()
    print(get_hex(signature))

    # task 6
    test_string = b'Hello World'
    subject_cert_x509_data = open(SUBJECT_CERT_FILE_PATH, "rb").read()
    subject_cert_x509 = x509.load_pem_x509_certificate(subject_cert_x509_data, default_backend())
    pubkey = subject_cert_x509.public_key()
    algo_256 = hashes.SHA256()
    test_padding = padding.MGF1(algo_256)
    test_padding = padding.OAEP(mgf=test_padding, algorithm=algo_256, label=None)
    encrypted_string = pubkey.encrypt(test_string, test_padding)
    print()
    print(get_hex(encrypted_string))


if  __name__ == "__main__":
    args = parse()
    tasks(args)