Get an RSA modulus from a server

getModulus.py

import ssl
from Crypto.Util import asn1
from OpenSSL.crypto import FILETYPE_PEM, FILETYPE_ASN1, load_certificate, dump_privatekey

def getModulusFromServer(host, port=443):

	try:
		# get cert from server
		cert = ssl.get_server_certificate((host,port))
		# load certificate
		certObj = load_certificate(FILETYPE_PEM, cert)
		# get public key from cert
		pub_asn1 = dump_privatekey(FILETYPE_ASN1, certObj.get_pubkey())
		# decode public key
		pub_der=asn1.DerSequence()
		pub_der.decode(pub_asn1)
		# get modulus
		pub_modulus=pub_der[1]

	except:
		pub_modulus = -1

	return pub_modulus