Python 使用 M2Crypto 通过 S/MIME 对消息进行签名

我现在花了几个小时，但找不到我的错误。我想要一个简单的例程来创建 S/MIME 签名消息，稍后可以与 smtplib 一起使用。

这是我到目前为止所拥有的：

#!/usr/bin/python2.7
# -*- coding: utf-8 -*-

from __future__ import print_function
from __future__ import absolute_import

import sys

from M2Crypto import BIO, Rand, SMIME

text = """Das ist ein einfacher Satz"""

sign_cert = "cert.pem"
sign_key = "key.pem"

# -----------------------------------------------------------------------------

class SignError(Exception):
    pass


def sign(msg):
    if "unsigned" not in msg:
        raise SignError()

    # Seed the PRNG.
    Rand.load_file('.rnd', -1)

    # Make a MemoryBuffer of the message.
    msg_bio = BIO.MemoryBuffer(msg["unsigned"])

    signer = SMIME.SMIME()

    # Load key and certificate
    try:
        signer.load_key(sign_key, sign_cert)
    except BIO.BIOError:
        raise SignError()

    p7 = signer.sign(msg_bio, flags=SMIME.PKCS7_TEXT)

    # Recreate buf.
    msg_bio = BIO.MemoryBuffer(msg["unsigned"])

    # Output p7 in mail-friendly format.
    out = BIO.MemoryBuffer()
    out.write('From: <[email protected] /cdn-cgi/l/email-protection>\r\n')
    out.write("To: <[email protected] /cdn-cgi/l/email-protection>\r\n")
    out.write("Subject: M2Crypto S/MIME testing\r\n")
    signer.write(out, p7, data_bio=msg_bio, flags=SMIME.PKCS7_TEXT)

    msg["signed"] = out.read()
    out.close()

    # Save the PRNG's state.
    Rand.save_file(".rnd")


if __name__ == "__main__":
    msg = dict(unsigned=text)

    try:
        sign(msg)
    except SignError:
        print("Unable to sign message", file=sys.stderr)

    if "signed" in msg:
        print(msg["signed"])

    sys.exit()

# vim: ts=4 sw=4 expandtab

不幸的是，它只产生：

From: <[email protected] /cdn-cgi/l/email-protection>
To: <[email protected] /cdn-cgi/l/email-protection>
Subject: M2Crypto S/MIME testing
MIME-Version: 1.0
Content-Type: multipart/signed; protocol="application/x-pkcs7-signature"; micalg="sha-256"; boundary="----B9B56E4AFF9BD5BC9B3B8FEDDE632A4C"

This is an S/MIME signed message

------B9B56E4AFF9BD5BC9B3B8FEDDE632A4C
Content-Type: text/plain

Das ist ein einfacher Satz

如果我添加代码来显示 p7，我可以看到它创建了一个数据 blob。

我使用原始证书和密钥。但我之前也用自签名证书测试过。总是相同的结果。

我检查了 M2Crypto 中的几乎所有示例，它看起来都一样（对我来说）。我在这里缺少什么？

非常感谢您提前提供帮助:-)

这已经晚了几年了，但对于任何来自谷歌的人来说，因为它的特点很突出，试试这个：

p7 = smime.sign(buf, SMIME.PKCS7_DETACHED)

out = BIO.MemoryBuffer()
out.write('From: %s\n' % sender)
out.write('To: %s\n' % to)
out.write('Subject: %s\n' % subject)

buf = BIO.MemoryBuffer(msg_str)

smime.write(out, p7, buf)