How to digitally sign a message with M2Crypto using the keys within a DER format certificate

Posted by Pablo Santos on Stack Overflow See other posts from Stack Overflow or by Pablo Santos
Published on 2010-03-08T13:00:56Z Indexed on 2010/03/08 23:51 UTC
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Hi everyone.

I am working on a project to implement digital signatures of outgoing messages and decided to use M2Crypto for that.

I have a certificate (in DER format) from which I extract the keys to sign the message. For some reason I keep getting an ugly segmentation fault error when I call the "sign_update" method.

Given the previous examples I have read here, I am clearly missing something.

Here is the example I am working on:

from M2Crypto.X509 import *

cert = load_cert( 'certificate.cer', format=0 )
Pub_key = cert.get_pubkey()
Pub_key.reset_context(md='sha1')
Pub_key.sign_init()
Pub_key.sign_update( "This should be good." )

print Pub_key.sign_final()

Thanks in advance for the help,

Pablo

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