[Python] Not able to sign emails using Dkimpy

rohit_k · 08-27-2018, 12:21 PM

I am trying to sign email using Python and dkimpy. Following is my code:

Code:

            try:
                with open(private_key) as file:
                    key = file.read()
            except Exception,error:
                raise Exception("Cannot open private key file %s. Error seen: %s" %(private_key,str(error)))
            else:
                sig = dkim.sign(
                        message=msg.as_string(),
                        selector=str(selector),
                        domain=sender_domain,
                        privkey=key,
                        include_headers=headers_list,
                        canonicalize=canonicalize,
                        signature_algorithm=sign_algo,
                        )
            # add DKIM-Signature header to email
            msg.add_header('DKIM-Signature',sig.lstrip("DKIM-Signature: "))

            # create a new email file. New email file will have 'signed_' prefix
            base_dir = os.path.dirname(eml)
            signed_email = os.path.basename(eml)
            signed_email = os.path.join(base_dir,'signed_' + signed_email)
            with open(signed_email, "w") as file:
                file.write(msg.as_string())

When header canonicalize is 'relaxed', my code works well. But when header canonicalize is 'simple', email is not correctly signed.

Code:

canonicalize = ('relaxed', 'simple')  <--- works
canonicalize = ('simple', 'relaxed')  <--- NOT WORKING

I am using 'opendkim-testmsg' to test signed emails

Code:

opendkim-testmsg < signed_test.msg
opendkim-testmsg: dkim_eom(): Bad signature

I am not able to figure out whats wrong

Please help.

TB0ne · 08-27-2018, 01:40 PM

Quote:

Originally Posted by rohit_k

I am trying to sign email using Python and dkimpy. Following is my code:

Code:

            try:
                with open(private_key) as file:
                    key = file.read()
            except Exception,error:
                raise Exception("Cannot open private key file %s. Error seen: %s" %(private_key,str(error)))
            else:
                sig = dkim.sign(
                        message=msg.as_string(),
                        selector=str(selector),
                        domain=sender_domain,
                        privkey=key,
                        include_headers=headers_list,
                        canonicalize=canonicalize,
                        signature_algorithm=sign_algo,
                        )
            # add DKIM-Signature header to email
            msg.add_header('DKIM-Signature',sig.lstrip("DKIM-Signature: "))

            # create a new email file. New email file will have 'signed_' prefix
            base_dir = os.path.dirname(eml)
            signed_email = os.path.basename(eml)
            signed_email = os.path.join(base_dir,'signed_' + signed_email)
            with open(signed_email, "w") as file:
                file.write(msg.as_string())

When header canonicalize is 'relaxed', my code works well. But when header canonicalize is 'simple', email is not correctly signed.

Code:

canonicalize = ('relaxed', 'simple')  <--- works
canonicalize = ('simple', 'relaxed')  <--- NOT WORKING

I am using 'opendkim-testmsg' to test signed emails

Code:

opendkim-testmsg < signed_test.msg
opendkim-testmsg: dkim_eom(): Bad signature

How did you configure opendkim.conf? And have you been through the docs on this?
https://gathman.org/pydkim/

rohit_k · 08-27-2018, 10:25 PM

opendkim.conf will not come into picture here. I am directly using Python module to sign email.

TB0ne · 08-28-2018, 12:59 PM

Quote:

Originally Posted by rohit_k

opendkim.conf will not come into picture here. I am directly using Python module to sign email.

Then where are you getting the signature? Your keys?? You've not posted the complete code...where did you get it?

And there are MANY Python programs that do DKIM signing you can look at as examples.
https://russell.ballestrini.net/quic...l-with-python/