decrypt DER-encoded x509 RSA certificate

from cryptography import x509
from cryptography.hazmat.backends import default_backend
from cryptography.hazmat.primitives import serialization
import base64

# Function to extract modulus from DER-encoded x509 RSA certificate
def extract_modulus_from_der(der_filename):
    with open(der_filename, 'rb') as f:
        der_data = f.read()

    # Load DER-encoded certificate
    cert = x509.load_der_x509_certificate(der_data, default_backend())

    # Extract public key and modulus
    public_key = cert.public_key()
    rsa_public_key = public_key.public_numbers()
    modulus = rsa_public_key.n

    return modulus

# Example usage
der_filename = '2048b-rsa-example-cert.der'
modulus = extract_modulus_from_der(der_filename)
print("Modulus (as decimal):", modulus)