class Pki:
    """
    Represent a Public Key Infrastructure
    """

    def __init__(self):
        pass

class Certificate:
    """
    Represent a Certificate
    """

    def __init__(self):
        # create a builder for the certificate
        builder = x509.CertificateBuilder(
            issuer_name=x509.Name([x509.NameAttribute(x509.oid.NameOID.COMMON_NAME, issuer)]),
            subject_name=x509.Name([x509.NameAttribute(x509.oid.NameOID.COMMON_NAME, subject)]),
            serial_number=x509.random_serial_number(),
            public_key=self.public_key,
            not_valid_before=valid_start,
            not_valid_after=valid_end,
        )