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Simple S/MIME e-mails with Python3

Project description

This library makes it simple to create S/MIME messages in Python. It supports signing (using RSA keys), encryption (using a public RSA key, in AES128-CBC, AES192-CBC or AES256-CBC modes) and the combination of both - where the message is first signed and the result is then encrypted (“enveloped”).

The foundation of python-smail is the oscrypto library which provides access to the C-bindings of OpenSSL and implements many high and low level functionality. Additionally asn1crypto is used which is “A fast, pure Python library for parsing and serializing ASN.1 structures.”.

Requirements

  • Python 3.5+
  • asn1crypto
  • oscrypto

Example

Encryption

The code below loads Bob’s public key in PEM format and uses it to encrypt the e-mail in S/MIME format:

import os
from email.mime.text import MIMEText
from email.utils import formatdate
from oscrypto import asymmetric
from smail import encrypt_message

message = MIMEText("This a plain text body!")
message['Date'] = formatdate(localtime=True)
message['From'] = "AliceRSA@example.com"
message['To'] = "BobRSA@example.com"
message['Subject'] = "Text Message - Encrypted"

cert = os.path.join('tests', 'testdata', 'BobRSASignByCarl.pem')

encrypted_message = encrypt_message(message, [cert])
print(encrypted_message.as_string())

Output:

MIME-Version: 1.0
Content-Type: application/pkcs7-mime; smime-type=enveloped-data; name=smime.p7m
Content-Transfer-Encoding: base64
Content-Disposition: attachment; filename=smime.p7m
Date: Tue, 17 Mar 2020 19:58:17 +0100
From: AliceRSA@example.com
To: BobRSA@example.com
Subject: Plain Text Message
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Signing

The code below loads Alice’s private and public key in PEM format and uses it to sign the e-mail in S/MIME format:

import os
from email.mime.text import MIMEText
from email.utils import formatdate
from smail import sign_message

message = MIMEText("This a plain text body!")
message['Date'] = formatdate(localtime=True)
message['From'] = "AliceRSA@example.com"
message['To'] = "BobRSA@example.com"
message['Subject'] = "Text Message - Signed"

cert_signer = os.path.join('tests', 'testdata', 'AliceRSASignByCarl.pem')
key_signer = os.path.join('tests', 'testdata', 'AlicePrivRSASign.pem')

signed_message = sign_message(message, key_signer, cert_signer)
print(signed_message.as_string())

Output:

MIME-Version: 1.0
Content-Type: multipart/signed; protocol="application/x-pkcs7-signature"; micalg="sha-256"; boundary="----39D1127DF0061CD9BB50644B14CCEF86"
Date: Tue, 17 Mar 2020 20:02:11 +0100
From: AliceRSA@example.com
To: BobRSA@example.com
Subject: Plain Text Message

This is an S/MIME signed message

------39D1127DF0061CD9BB50644B14CCEF86
Content-Type: text/plain; charset="us-ascii"
MIME-Version: 1.0
Content-Transfer-Encoding: 7bit

This a plain text body!
------39D1127DF0061CD9BB50644B14CCEF86
Content-Type: application/x-pkcs7-signature; name="smime.p7s"
Content-Transfer-Encoding: base64
Content-Disposition: attachment; filename="smime.p7s"

MIIEIwYJKoZIhvcNAQcCoIIEFDCCBBACAQExDzANBglghkgBZQMEAgEFADALBgkq
hkiG9w0BBwGgggIwMIICLDCCAZWgAwIBAgIQRjRrx4AAVrwR024uxBCzsDANBgkq
hkiG9w0BAQUFADASMRAwDgYDVQQDEwdDYXJsUlNBMB4XDTk5MDkxOTAxMDg0N1oX
DTM5MTIzMTIzNTk1OVowEzERMA8GA1UEAxMIQWxpY2VSU0EwgZ8wDQYJKoZIhvcN
AQEBBQADgY0AMIGJAoGBAOCJczmN2PX16Id2OX9OsAW7U4PeD7er3H3HdSkNBS5t
Et+mhibU0m+qWCn8l+z6glEPMIC+sVCeRkTxLLvYMs/GaG8H2bBgrL7uNAlqE/X3
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FbsNV6kaFBOrfkgLICl/a6HaYu9xCHdS7bmiLlDs6qeofmyRAZgUBdDKySm+yjZc
V1VLPuFuL9+BDcXarthOSnn4wbdRBhceRu7w8OnyoTtrwP58c0MiQVtyBQq1FuPZ
WBKduWYjIg==

------39D1127DF0061CD9BB50644B14CCEF86--

Sign and Encrypt

The code below loads Alice’s private and public key and also Bob’s public key in PEM format and uses it to sign and encrypt the e-mail (from Alice to Bob) in S/MIME format:

import os
from email.mime.text import MIMEText
from email.utils import formatdate
from oscrypto import asymmetric
from smail import sign_and_encrypt_message

message = MIMEText("This a plain text body!")
message['Date'] = formatdate(localtime=True)
message['From'] = "AliceRSA@example.com"
message['To'] = "BobRSA@example.com"
message['Subject'] = "Text Message - Signed and Encrypted"

cert_signer = os.path.join('tests', 'testdata', 'AliceRSASignByCarl.pem')
key_signer = os.path.join('tests', 'testdata', 'AlicePrivRSASign.pem')

cert = os.path.join('tests', 'testdata', 'BobRSASignByCarl.pem')

signed_encrypted_message = sign_and_encrypt_message(message, key_signer, cert_signer, [cert])
print(signed_encrypted_message.as_string())

Output:

MIME-Version: 1.0
Content-Type: application/pkcs7-mime; smime-type=enveloped-data; name=smime.p7m
Content-Transfer-Encoding: base64
Content-Disposition: attachment; filename=smime.p7m
Date: Tue, 17 Mar 2020 20:05:34 +0100
From: AliceRSA@example.com
To: BobRSA@example.com
Subject: Text Message - Signed and Encrypted

MIIIuQYJKoZIhvcNAQcDoIIIqjCCCKYCAQAxgb4wgbsCAQAwJjASMRAwDgYDVQQD
EwdDYXJsUlNBAhBGNGvHgABWvBHTbi7NXXHQMAsGCSqGSIb3DQEBAQSBgH5C7eTN
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Acknowledgements

Python SMAIL is heavily inspired by python-smime and is actually a fork of that code base. All credits go to original Author(s).

License

This software is licensed under the Apache License 2.0. See the LICENSE file in the top distribution directory for the full license text.

Versioning

This software follows Semantic Versioning

Project details


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