python - M2Crypto:从不透明签名的 S/MIME (pkcs7-mime) 中提取消息

Question

我在从不透明签名的 S/MIME 消息中提取消息数据时遇到问题，例如:

To: ngps@post1.com
From: ngps@mpost1.com
Subject: testing
MIME-Version: 1.0
Content-Disposition: attachment; filename="smime.p7m"
Content-Type: application/pkcs7-mime; smime-type=signed-data; name="smime.p7m"
Content-Transfer-Encoding: base64

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这实际上是一个不透明的 S/MIME 签名(未加密)消息 opaque.p7，由 demo/smime/ 的 M2Crypto (0.21.1) sign 函数生成测试.py。数据显然包含消息，它可以被揭示，例如通过:openssl smime -verify -noverify -in opaque.p7。

不幸的是，当我想获取数据时:

p7, data = M2Crypto.SMIME.smime_load_pkcs7('opaque.p7')

不幸的是，data 是None。这只是不透明 S/MIME 变体的问题，因为同样适用于 clear.p7。

我猜这可能是一些兼容性问题，我的 OpenSSL 版本是 1.0.1e (Debian Wheezy)..我想知道是否有人让它工作。

更新

这是修改后的 test.py(原始 here)的输出，以证明对于清晰和不透明的 S/MIME 消息，M2Crypto 正确提取签名者证书，但未从不透明的 SMIME 中提取任何数据:

test encrypt/decrypt... ok
test sign & save... ok
test load & verify opaque... ok
  DATA: ''
  SIGNERS: ['C=AU, ST=Some-State, O=Internet Widgits Pty Ltd']
test load & verify clear... ok
  DATA: 'actual message'
  SIGNERS: ['C=AU, ST=Some-State, O=Internet Widgits Pty Ltd']
test sign/verify... ok

test.py 已打补丁，因为它在很多地方都失败了..

--- M2Crypto-0.21.1.orig/demo/smime/test.py 2011-01-15 20:10:06.000000000 +0100
+++ M2Crypto-0.21.1/demo/smime/test.py  2013-07-16 16:37:57.224845942 +0200
@@ -6,18 +6,7 @@
 
 from M2Crypto import BIO, Rand, SMIME, X509
 
-ptxt = """
-S/MIME - Secure Multipurpose Internet Mail Extensions [RFC 2311, RFC 2312] - 
-provides a consistent way to send and receive secure MIME data. Based on the
-popular Internet MIME standard, S/MIME provides the following cryptographic
-security services for electronic messaging applications - authentication,
-message integrity and non-repudiation of origin (using digital signatures)
-and privacy and data security (using encryption).
-
-S/MIME is built on the PKCS #7 standard. [PKCS7]
-
-S/MIME is implemented in Netscape Messenger and Microsoft Outlook.
-"""
+ptxt = 'actual message'
 
 def makebuf():
     buf = BIO.MemoryBuffer(ptxt)
@@ -27,14 +16,14 @@
     print 'test sign & save...',
     buf = makebuf()
     s = SMIME.SMIME()
-    s.load_key('client.pem')
-    p7 = s.sign(buf)
+    s.load_key('client_.pem')
+    p7 = s.sign(buf, flags=SMIME.PKCS7_DETACHED)
     out = BIO.openfile('clear.p7', 'w')
     out.write('To: ngps@post1.com\n')
     out.write('From: ngps@post1.com\n')
     out.write('Subject: testing\n')
     buf = makebuf() # Recreate buf, because sign() has consumed it.
-    s.write(out, p7, buf)
+    s.write(out, p7, buf, flags=SMIME.PKCS7_DETACHED)
     out.close()
 
     buf = makebuf()
@@ -50,36 +39,42 @@
 def verify_clear():
     print 'test load & verify clear...',
     s = SMIME.SMIME()
-    x509 = X509.load_cert('client.pem')
+    x509 = X509.load_cert('client_.pem')
     sk = X509.X509_Stack()
     sk.push(x509)
     s.set_x509_stack(sk)
     st = X509.X509_Store()
-    st.load_info('ca.pem')
+    st.load_info('client_.pem')
     s.set_x509_store(st)
     p7, data = SMIME.smime_load_pkcs7('clear.p7')
-    v = s.verify(p7)
-    if v:
+    data_s = data.read() if isinstance(data, BIO.BIO) else ''
+    v = s.verify(p7, BIO.MemoryBuffer(data_s))
+    if v and (v == ptxt):
         print 'ok'
     else:
         print 'not ok'
+    print '  DATA: %r' % (data_s,)
+    print '  SIGNERS: %r' % ([ x.get_subject().as_text() for x in p7.get0_signers(sk)],)
     
 def verify_opaque():
     print 'test load & verify opaque...',
     s = SMIME.SMIME()
-    x509 = X509.load_cert('client.pem')
+    x509 = X509.load_cert('client_.pem')
     sk = X509.X509_Stack()
     sk.push(x509)
     s.set_x509_stack(sk)
     st = X509.X509_Store()
-    st.load_info('ca.pem')
+    st.load_info('client_.pem')
     s.set_x509_store(st)
     p7, data = SMIME.smime_load_pkcs7('opaque.p7')
-    v = s.verify(p7, data)
-    if v:
+    data_s = data.read() if isinstance(data, BIO.BIO) else ''
+    v = s.verify(p7, makebuf()) # here we are verify against ptxt, since we get no data
+    if v and (v == ptxt):
         print 'ok'
     else:
         print 'not ok'
+    print '  DATA: %r' % (data_s,)
+    print '  SIGNERS: %r' % ([ x.get_subject().as_text() for x in p7.get0_signers(sk)],)
     
 def verify_netscape():
     print 'test load & verify netscape messager output...',
@@ -102,31 +97,32 @@
     s = SMIME.SMIME()
 
     # Load a private key.
-    s.load_key('client.pem')
+    s.load_key('client_.pem')
 
     # Sign.
-    p7 = s.sign(buf)
+    p7 = s.sign(buf, flags=SMIME.PKCS7_DETACHED)
 
     # Output the stuff.
+    buf = makebuf()
     bio = BIO.MemoryBuffer()
-    s.write(bio, p7, buf)
+    s.write(bio, p7, buf, flags=SMIME.PKCS7_DETACHED)
     
     # Plumbing for verification: CA's cert.
     st = X509.X509_Store()
-    st.load_info('ca.pem')
+    st.load_info('client_.pem')
     s.set_x509_store(st)
 
     # Plumbing for verification: Signer's cert.
-    x509 = X509.load_cert('client.pem')
+    x509 = X509.load_cert('client_.pem')
     sk = X509.X509_Stack()
     sk.push(x509)
     s.set_x509_stack(sk)
 
     # Verify.
     p7, buf = SMIME.smime_load_pkcs7_bio(bio)
-    v = s.verify(p7, flags=SMIME.PKCS7_DETACHED)
-    
-    if v:
+    v = s.verify(p7, buf, flags=SMIME.PKCS7_DETACHED)
+
+    if v and (v == ptxt):
         print 'ok'
     else:
         print 'not ok'

client.pem 包含过期证书，因此它使用自签名的 client_.pem，它由 openssl req -new -x509 -newkey rsa -nodes -keyout client_.pem -out client_.pem

(请注意，测试加载和验证不透明测试用例假装成功，因为验证步骤已更改为针对原始已知文本进行验证)

Answer 1

我认为这里的主要误解是，对于“multipart/signed”以外的 MIME 类型，smime_load_pkcs7() 是意思 在元组的第二部分返回 None，而 SMIME.SMIME.verify() 意味着 第二个参数无。

当你调用s.verify(a, b)时，它并不意味着“验证a中的签名与消息b”，意思是“验证 PKCS7 结构 a 是否具有有效签名，给定 x509 存储和 SMIME 对象 s 上的堆栈。哦，如果 a 有一个分离的消息，你可以在 b 中找到消息部分。"

如果你想修复你的verify_opaque()函数，把data_s的东西一起拿出来，然后放回原来的s.verify(p7 , 数据) 调用。如果 v == ptxt，则原始消息的提取按预期进行，并且签名得到验证。如果您仍想打印出“DATA:”行，请使用 v 而不是 data_s。

如果您的问题是关于如何从任意不透明签名消息中获取原始消息数据，看起来您应该获得有效的 M2Crypto.SMIME.SMIME 上下文 s 并用它调用 s.verify()!这不是我以前需要自己完成的操作，所以我可能会遗漏一些简单的 API，但据我所知，M2Crypto 没有公开任何更简单的方法。至少，如果你没有一组有效的证书来检查，或者你不关心，你可以将 PKCS7_NOVERIFY 标志传递给 s.verify() 就像您使用 openssl cmdline 工具一样调用。