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@russau
Last active Jun 13, 2020
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Verify EC2 PKCS7 Signature in Python
-----BEGIN CERTIFICATE-----
MIIC7TCCAq0CCQCWukjZ5V4aZzAJBgcqhkjOOAQDMFwxCzAJBgNVBAYTAlVTMRkw
FwYDVQQIExBXYXNoaW5ndG9uIFN0YXRlMRAwDgYDVQQHEwdTZWF0dGxlMSAwHgYD
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IFN0YXRlMRAwDgYDVQQHEwdTZWF0dGxlMSAwHgYDVQQKExdBbWF6b24gV2ViIFNl
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MXrs3IgIb6+hUIB+S8dz8/mmO0bpr76RoZVCXYab2CZedFut7qc3WUH9+EUAH5mw
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7HX32MxXYruse9ACFBNGmdX2ZBrVNGrN9N2f6ROk0k9K
-----END CERTIFICATE-----
# https://stackoverflow.com/a/60840416/109102
sudo apt-get install build-essential libssl-dev swig python3-dev
pip3 install M2Crypto
# Thanks to:
# https://darthnull.org/security/2012/02/21/verifying-a-detatched-smime-signature-in-python/
# https://tools.ietf.org/doc/python-m2crypto/howto.smime.html#VERIFY
from M2Crypto import SMIME, X509, BIO
import requests
# Instantiate an SMIME object
s = SMIME.SMIME()
# Load the signer's cert.
# certificate from https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/verify-pkcs7.html
x509 = X509.load_cert('certificate')
sk = X509.X509_Stack()
sk.push(x509)
s.set_x509_stack(sk)
# Load the signer's CA cert. In this case, because the signer's
# cert is self-signed, it is the signer's cert itself.
st = X509.X509_Store()
st.load_info('certificate')
s.set_x509_store(st)
# Load the data, verify it.
r = requests.get("http://169.254.169.254/latest/dynamic/instance-identity/pkcs7")
pkcs7 = """-----BEGIN PKCS7-----
%s
-----END PKCS7-----""" % r.text
buf = BIO.MemoryBuffer(pkcs7.encode())
p7 = SMIME.load_pkcs7_bio(buf)
v = s.verify(p7)
print(v.decode())
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