SAML Signature Verification Using Python/M2Crypto

I'm attempting to use M2Crypto to verify a signature contained in an XML response returned from my SSO/SAML provider in my django/python app, but I can't seem to get it to work. My

Solution 1:

You were so close! You should pass to verify_update the signed_info, and then to verify_final pass the signature.

You do need to make sure that your signed_info is correctly canonicalized before verifying the signature.

Here is the correct method:

def verify_signature(signed_info, cert, signature):
    from M2Crypto import EVP, RSA, X509

    x509 = X509.load_cert_string(base64.decodestring(cert), X509.FORMAT_DER)
    pubkey = x509.get_pubkey().get_rsa()
    verify_EVP = EVP.PKey()
    verify_EVP.assign_rsa(pubkey)
    verify_EVP.reset_context(md='sha1')
    verify_EVP.verify_init()

    verify_EVP.verify_update(signed_info)
    result = verify_EVP.verify_final(signature.decode('base64'))

    return result

Solution 2:

FYI, I was facing the same problem as you, and found no useful software for validating XML signatures in Python, so I wrote a new library: https://github.com/kislyuk/signxml.

from lxml import etree
from signxml import xmldsig

with open("saml2_idp_metadata.xml", "rb") as fh:
    cert = etree.parse(fh).find("//ds:X509Certificate").text

root = ElementTree.fromstring(signature_data)
xmldsig(root).verify(x509_cert=cert)