M2Crypto:从不透明的签名S/MIME中提取消息(pkcs7-mime)

Question

我在从不透明的签名S/MIME消息中提取消息数据时遇到了问题，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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2q1YcztjY4drOJi6CH8bHOlfb1nXr/mBQuijLA5wFl22PDGTrlZ5

它实际上是由M2Crypto的(0.21.1) opaque.p7函数从演示/模拟/test.py生成的一个不透明的S/MIME签名(而不是加密)消息test.py。数据显然包含了消息，它可以通过：openssl smime -verify -noverify -in opaque.p7来显示。

不幸的是，当我想通过以下方法获取数据时：

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

不幸的是，data是None。这只是不透明的S/MIME变体的一个问题，因为clear.p7也是如此。

我想这可能是一些兼容性问题，我的OpenSSL版本是1.0.1e (Debian )。我想知道是不是有人让它起作用了。

更新

以下是修改后的test.py (原始这里)的输出，以说明对于清晰和不透明的S/MIME消息，M2Crypto正确提取签名者证书，但不从不透明的SMIME提取数据：

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被修补了，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包含过期的证书，因此它使用由openssl req -new -x509 -newkey rsa -nodes -keyout client_.pem -out client_.pem生成的自签名client_.pem。

(请注意，测试加载&验证不透明的测试用例假装成功，因为验证步骤被更改为根据原始已知文本进行验证)

Answer 1

我认为这里主要的误解是，对于"multipart/signed“以外的MIME类型，smime_load_pkcs7()是指在元组的第二部分返回None，而SMIME.SMIME.verify()则是将None作为其第二个参数。

当您调用s.verify(a, b)时，它并不意味着“验证a中的签名是否与消息b匹配”，它意味着“根据SMIME对象s上的x509存储和堆栈，验证PKCS7结构a有一个有效的签名。哦，如果a有一条独立的消息，您可以在b中找到消息部分。”

如果您想要修复您的verify_opaque()函数，请全部取出data_s内容，并将原始的s.verify(p7, data)调用放回去。如果是v == ptxt，那么提取原始消息就像预期的那样进行，并验证签名。如果您仍然希望打印出"DATA:“行，请使用v而不是data_s。

如果您的问题是如何从任意的不透明签名消息中获取原始消息数据，那么看起来您应该得到一个有效的M2Crypto.SMIME.SMIME上下文s并使用它调用s.verify()！这不是我以前需要做的操作，所以我可能缺少一些简单的API，但据我所知，M2Crypto并没有公开任何更简单的方法。至少，如果您没有一组有效的证书可供检查，或者您并不关心，您可以像使用openssl工具一样，将PKCS7_NOVERIFY标志传递给s.verify()调用。