Verify S/MIME Signature

Python example to verify an S/MIME signature and unwrap the S/MIME to get the original MIME prior to signing/encrypting.

Download Chilkat Python Library

import sys
import chilkat

mime = chilkat.CkMime()

#  Any string argument automatically begins the 30-day trial.
success = mime.UnlockComponent("30-day trial")
if (success != True):
    print "MIME component unlock failed"
    sys.exit()

#  Load an S/MIME message from a file:
success = mime.LoadMimeFile("signedMime.txt")
if (success != True):
    print mime.lastErrorText()
    sys.exit()

#  The ContainsEncryptedParts/ContainsSignedParts methods
#  can be called to determine if the MIME is encrypted and/or signed:
isEncrypted = mime.ContainsEncryptedParts()
isSigned = mime.ContainsSignedParts()

#  We don't want the "unwrap extras".  You'll see what those
#  are in a few moments...
mime.put_UnwrapExtras(False)

#  To verify the signature, call UnwrapSecurity.  This will
#  verify the signature(s) and decrypt the S/MIME and restore
#  the MIME to the unsigned/unencrypted state.
#  The results of what was found are present in the MIME object's
#  properties, as well as extra header fields that are added
#  to the unwrapped MIME.
success = mime.UnwrapSecurity()
if (success != True):
    #  UnwrapSecurity returns _TRUE_ if all signatures were
    #  verified and all parts decrypted.
    print mime.lastErrorText()
    sys.exit()

#  The mime.UnwrapExtras property controls whether or not
#  these additional fields are added to the unwrapped MIME:
# 
#  X-NumPartsSigned: 1
#  X-SignaturesValid: yes
#  X-NumPartsEncrypted: 1
#  X-Decrypted: no
# 
#  The X-NumPartsSigned/X-SignaturesValid headers are added
#  if the MIME was signed.
# 
#  The X-NumPartsEncrypted/X-Decrypted headers are added
#  if the MIME was encrypted.
# 

#  If the MIME was signed, get the certificate used for signing.
if (isSigned == True):
    #  The NumSignerCerts property indicates how many certificates
    #  were used for signing.  This example will assume the value is 1.
    #  To get the 1st signer cert, call GetSignerCert with an index of 0:

    signerCert = mime.GetSignerCert(0)
    if (not (signerCert == None )):
        print "**** Signer Cert: " + signerCert.subjectCN()

#  If the MIME was encrypted, get the certificate used for encryption:
if (isEncrypted == True):
    #  The NumEncryptCerts property indicates how many certificates
    #  were used for encrypting.  This example will assume the value is 1.
    #  To get the 1st encrypt cert, call GetEncryptCert with an index of 0:

    encryptCert = mime.GetEncryptCert(0)
    if (not (encryptCert == None )):
        print "**** Encrypt Cert: " + encryptCert.subjectCN()

#  Display the unwrapped MIME:
print mime.getMime()

#  Save the unwrapped MIME to a file:
mime.SaveMime("unwrappedMime.txt")