createCert.py

# Author Vysakh P Pillai
# Includes some code from  Simon Davy
#
# Permission is hereby granted, free of charge, to any person obtaining a copy
# of this software and associated documentation files (the "Software"), to deal
# in the Software without restriction, including without limitation the rights
# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
# copies of the Software, and to permit persons to whom the Software is
# furnished to do so, subject to the following conditions:
#
# The above copyright notice and this permission notice shall be included in
# all copies or substantial portions of the Software.
#
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
# SOFTWARE.


from datetime import datetime, timedelta
import ipaddress, socket, binascii
from string import Template
from netifaces import interfaces, ifaddresses, AF_INET
from random import randint

def generate_selfsigned_cert(hostname, ip_addresses=None, key=None, der=True):
    """Generates self signed certificate for a hostname, and optional IP addresses."""
    from cryptography import x509
    from cryptography.x509.oid import NameOID
    from cryptography.hazmat.primitives import hashes
    from cryptography.hazmat.backends import default_backend
    from cryptography.hazmat.primitives import serialization
    from cryptography.hazmat.primitives.asymmetric import rsa
    from cryptography.hazmat.primitives.asymmetric import ec
    
    # Generate our key
    if key is None:
        key = ec.generate_private_key(
            ec.SECP256R1(), 
            default_backend()
        )
#    key = rsa.generate_private_key(
#            public_exponent=65537,
#            key_size=2048,
#            backend=default_backend(),
#        )
        
    name = x509.Name([
        x509.NameAttribute(NameOID.COMMON_NAME, hostname)
    ])
 
    # best practice seem to be to include the hostname in the SAN, which *SHOULD* mean COMMON_NAME is ignored.    
    alt_names = [x509.DNSName(hostname)]
    
    # allow addressing by IP, for when you don't have real DNS (common in most testing scenarios 
    if ip_addresses:
        for addr in ip_addresses:
            # openssl wants DNSnames for ips...
            alt_names.append(x509.DNSName(addr))
            # ... whereas golang's crypto/tls is stricter, and needs IPAddresses
            # note: older versions of cryptography do not understand ip_address objects
            alt_names.append(x509.IPAddress(ipaddress.ip_address(addr)))
    
    san = x509.SubjectAlternativeName(alt_names)
    
    # path_len=0 means this cert can only sign itself, not other certs.
    basic_contraints = x509.BasicConstraints(ca=True, path_length=0)
    now = datetime.utcnow()
    cert = (
        x509.CertificateBuilder()
        .subject_name(name)
        .issuer_name(name)
        .public_key(key.public_key())
        .serial_number(randint(0,2147483647))
        .not_valid_before(now)
        .not_valid_after(now + timedelta(days=10*365))
        .add_extension(basic_contraints, False)
        .add_extension(san, False)
        .sign(key, hashes.SHA256(), default_backend())
    )
    cert_pem = cert.public_bytes(encoding=serialization.Encoding.PEM)
    key_pem = key.private_bytes(
        encoding=serialization.Encoding.PEM,
        format=serialization.PrivateFormat.TraditionalOpenSSL,
        encryption_algorithm=serialization.NoEncryption(),
    )

    if der:
        cert_der = cert.public_bytes(encoding=serialization.Encoding.DER)
        key_der = key.private_bytes(
            encoding=serialization.Encoding.DER,
            format=serialization.PrivateFormat.TraditionalOpenSSL,
            encryption_algorithm=serialization.NoEncryption(),
        )
        return  cert_pem, key_pem, cert_der, key_der
    else:
        return cert_pem, key_pem

def make_sublist_group(lst: list, grp: int) -> list:
    """
    Group list elements into sublists.
    make_sublist_group([1, 2, 3, 4, 5, 6, 7], 3) = [[1, 2, 3], [4, 5, 6], 7]
    """
    return [lst[i:i+grp] for i in range(0, len(lst), grp)]

def do_convension(content: bytes) -> str:
    hexstr = binascii.hexlify(content).decode("UTF-8")
    hexstr = hexstr.upper()
    array = ["0x" + hexstr[i:i + 2] + "" for i in range(0, len(hexstr), 2)]
    array = make_sublist_group(array, 10)
    
    return sum(len(a) for a in array ), "\n".join([", ".join(e) + ", " for e in array])


#Creating a Certificate
hostname = socket.gethostname()    

cert_pem,key_pem, cert_der, key_der=generate_selfsigned_cert(hostname,ip_addresses=["192.168.1.51"])
with open('certnKey.crt', 'w') as file: 
    file.write(cert_pem.decode("UTF-8"))
    file.write(key_pem.decode("UTF-8"))

with open('cert.der', 'wb') as file: 
    file.write(cert_der)
with open('key.der', 'wb') as file: 
    file.write(key_der)

cer_length , cerArray=do_convension(cert_der)

certHeaderTemplate=Template("""
/*GENERATED FILE*/

#ifndef _CERTS_TEST_H_
#define _CERTS_TEST_H_

static const unsigned char ca_cert_der[] =
{
$caCert
};

/* size is $ceCertSize */
static const int sizeof_ca_cert_der = sizeof(ca_cert_der);

#endif /*_CERTS_TEST_H_*/
""")

with open('cert_header.h', 'w') as file: 
    file.write(certHeaderTemplate.substitute(caCert=cerArray,ceCertSize=cer_length))