How can I retrieve the TLS/SSL peer certificate of a remote host using python?

Question

I need to scan through a list of IPs and retrieve the common name from the certificate on that IP (for every IP that allows port 443 connections). I have been able to successfully do this using the sockets and ssl modules. It works for all IPs with valid, signed certificates but it isn't working for self-signed certificates.

If I use this method, it requires a valid cert that is verified by my CA-bundle:

from socket import socket
import ssl

s = socket()
c = ssl.wrap_socket(s,cert_reqs=ssl.CERT_REQUIRED, ca_certs='ca-bundle.crt')
c.connect(('127.0.0.1', 443))

print c.getpeercert()

If I remove the cert_reqs=ssl.CERT_REQUIRED then it connects but doesn't get the certificate at all.

How can I retrieve the common name for a certificate on an IP whether it validates against the ca-bundle or not?

Answer 1

The python ssl library seems like it only parses out the cert for you if it has a valid signature.

    """Returns a formatted version of the data in the
    certificate provided by the other end of the SSL channel.
    Return None if no certificate was provided, {} if a
    certificate was provided, but not validated."""

You can still get the server certificate with the ssl.get_server_certificate() function, but it returns it in PEM format. (Alternatively, you could call c.getpeercert(True), which returns the cert in binary DER format, whether it's validated or not.)

>>> print ssl.get_server_certificate(('server.test.com', 443))
-----BEGIN CERTIFICATE-----
MIID4zCCAsugAwIBA.....

From here, I would use M2Crypto or OpenSSL to read the cert and get values:

# M2Crypto
cert = ssl.get_server_certificate(('www.google.com', 443))
x509 = M2Crypto.X509.load_cert_string(cert)
x509.get_subject().as_text()
# 'C=US, ST=California, L=Mountain View, O=Google Inc, CN=www.google.com'

# OpenSSL
x509 = OpenSSL.crypto.load_certificate(OpenSSL.crypto.FILETYPE_PEM, cert)
x509.get_subject().get_components()
#[('C', 'US'),
# ('ST', 'California'),
# ('L', 'Mountain View'),
# ('O', 'Google Inc'),
# ('CN', 'www.google.com')]