java - 保留 SMIME 解密邮件的签名

Question

我找不到任何对我有帮助的东西。我在保留 smime 电子邮件的签名时遇到问题。我正在尝试获取加密的 smime 消息，解密它，然后将其保存到数据库(用于工作)。由于消息首先被签名然后被加密，所以我认为在解密后保留签名没有问题。我可以成功解密消息。当我尝试获取经过签名和加密的邮件时，它不起作用。我正在使用 Java (1.8) 和 bouncycaSTLe (jdk15on_154)。这一切都发生在一个具有静态方法的类中(因为我实际上是从 delphi 程序中调用解密)。

这是类(class):

    public static void startSMimeDecryption (final String encryptedPath, String decryptedPath) {
    logger.info("***  Start of sMIME decryption  ***"); //$NON-NLS-1$

    Properties props = System.getProperties();
    Session session = Session.getDefaultInstance(props, null);
    try {

        logger.info("Encrypted message: [" + encryptedPath + "]"); //$NON-NLS-1$ //$NON-NLS-2$
        File messageFile = new File(encryptedPath);
        String fileExtension = getFileExtension(messageFile);

        if (fileExtension != null) {

            MimeMessage m = null;

            if (fileExtension.toUpperCase().equals("EML")) { //$NON-NLS-1$

                try (FileInputStream streamIn = new FileInputStream(encryptedPath);) {
                    logger.info("Created FileInputStream."); //$NON-NLS-1$

                    m = new MimeMessage(session, streamIn);
                    logger.info("Created MimeMessage."); //$NON-NLS-1$
                } catch (IOException e) {
                    logger.error("Error while trying to read in message via stream. " + e.getMessage());
                    return;
                }   

            } else if (fileExtension.toUpperCase().equals("MSG")) { //$NON-NLS-1$
                m = createMimeMessageFromMsg(session, messageFile);
                logger.info("Created MimeMessage."); //$NON-NLS-1$
            } else {
                throw new InvalidFileException("Not a supported file type (extension). Only '*.eml' and '*.msg' are accepted."); //$NON-NLS-1$
            }

            if ((m.getFileName() != null) && (m.getFileName().toUpperCase().equals("SMIME.P7M") || Pattern.compile("^\\s*application\\/(x-)?pkcs7-mime.*$", Pattern.DOTALL).matcher(m.getContentType()).matches())) { //$NON-NLS-1$ //$NON-NLS-2$

                m = decryptMessage(m);

                logger.info("Saving decrypted message to file..."); //$NON-NLS-1$
                if (decryptedPath == null) {
                    String tempPath = messageFile.getAbsolutePath().substring(0, messageFile.getAbsolutePath().lastIndexOf(File.separator));
                    decryptedPath = tempPath + File.separator + FilenameUtils.removeExtension(messageFile.getName()) + "_decrypted.eml"; //$NON-NLS-1$
                }

                try (OutputStream str = Files.newOutputStream(Paths.get(decryptedPath))) {

                    m.writeTo(str);

                } catch (IOException e) {
                    logger.error("Failed to write to output stream. " + e.getMessage()); //$NON-NLS-1$
                    return;
                }

                logger.info("Decrypted message: [" + decryptedPath + "]"); //$NON-NLS-1$ //$NON-NLS-2$

            } else {
                throw new NotEncryptedMessageException("Not an encrypted message. Breaking up decryption."); //$NON-NLS-1$
            }

        } else {
            throw new InvalidFileException("No file extension found."); //$NON-NLS-1$
        }

    } catch (MessagingException | UnrecoverableKeyException | KeyStoreException | NoSuchAlgorithmException 
             | CMSException | InvalidFileException | InvalidMessageException e) {

        logger.error("Failed to read message. " + e.getMessage()); //$NON-NLS-1$
    } catch (NotEncryptedMessageException e) {
        logger.error(e.getMessage());
        System.exit(RETURNCODE_NODECRYPTION);
    }

    logger.info("***  End of sMIME decryption  ***"); //$NON-NLS-1$
}

private static MimeMessage createMimeMessageFromMsg (final Session session, final File messageFile) {
    MimeMessage mimeMsg = null;

    if (messageFile != null) {
        MAPIMessage mapiMsg = null;

        logger.info("Converting .msg to MimeMessage."); //$NON-NLS-1$
        try (NPOIFSFileSystem npoi = new NPOIFSFileSystem(messageFile)) {

            logger.info("Created NPOIFSFileSystem."); //$NON-NLS-1$

            mapiMsg = new MAPIMessage(npoi);
            logger.info("Created MAPIMessage."); //$NON-NLS-1$

            mimeMsg = new MimeMessage(session);
            logger.info("Creating MimeMessage..."); //$NON-NLS-1$

            // Header übertragen
            try {
                for (String current : mapiMsg.getHeaders()) {
                    try {

                        mimeMsg.addHeaderLine(current);

                    } catch (MessagingException e) {
                        logger.error("Could not add header line to MimeMessage. " + e.getMessage()); //$NON-NLS-1$
                    }
                }

                logger.info("Added header to MimeMessage."); //$NON-NLS-1$

            } catch (ChunkNotFoundException e) {
                logger.error("Could not retrieve header. " + e.getMessage()); //$NON-NLS-1$
            }

            // "Attachment" übertragen
            for (AttachmentChunks current : mapiMsg.getAttachmentFiles()) {
                try {

                    ByteArrayDataSource ds = new ByteArrayDataSource(current.getEmbeddedAttachmentObject(), "application/pkcs7-mime"); //$NON-NLS-1$
                    DataHandler dh = new DataHandler(ds);
                    mimeMsg.setDataHandler(dh);

                    logger.info("Added attachment to MimeMessage."); //$NON-NLS-1$

                } catch (MessagingException e) {
                    logger.error("Could not transfer attachment into MimeMessage. " + e.getMessage()); //$NON-NLS-1$
                }
            }

        } catch (IOException e) {
            logger.error("Error while trying to build MimeMessage. " + e.getMessage()); //$NON-NLS-1$
            mimeMsg = null;
        }
    }

    return mimeMsg;
}

private static MimeMessage decryptMessage(final MimeMessage encrypted) throws MessagingException, CMSException,
                                                                        KeyStoreException, UnrecoverableKeyException, 
                                                                        NoSuchAlgorithmException, InvalidMessageException {
    if (encrypted != null) {
        logger.info("Starting decrypting message..."); //$NON-NLS-1$
        KeyStore keystore = getKeyStore();

        SMIMEEnveloped message = new SMIMEEnveloped(encrypted);

        RecipientInformationStore recinfos = message.getRecipientInfos();
        Enumeration<String> aliases = keystore.aliases();
        RecipientInformation recid = null;
        String alias = null;

        logger.info("Decrypting message..."); //$NON-NLS-1$
        while ((recid == null) && aliases.hasMoreElements()) {
            alias = aliases.nextElement();
            if (keystore.isKeyEntry(alias)) {
                Certificate cert = keystore.getCertificate(alias);
                recid = recinfos.get(new JceKeyTransRecipientId((X509Certificate) cert));
            }
        }
        if (recid == null) {
            throw new RuntimeException("No decryption key found"); //$NON-NLS-1$
        }

        JceKeyTransEnvelopedRecipient recipient = new JceKeyTransEnvelopedRecipient((PrivateKey) keystore.getKey(alias, "changeit".toCharArray())); //$NON-NLS-1$

        byte[] content = recid.getContent(recipient);

        logger.info("Setting MimeMessage properties."); //$NON-NLS-1$
        MimeMessage decrypted = new MimeMessage(Session.getDefaultInstance(System.getProperties()), new ByteArrayInputStream(content));
        Enumeration<Header> headers = encrypted.getAllHeaders();
        while (headers.hasMoreElements()) {
            Header h = headers.nextElement();

            if (decrypted.getHeader(h.getName()) == null) {
                decrypted.addHeader(h.getName(), h.getValue());
            }

        }

        decrypted.saveChanges();            

        logger.info("Decrypted message."); //$NON-NLS-1$

        return decrypted;
    } else {
        throw new InvalidMessageException("Encrypted MimeMessage is null."); //$NON-NLS-1$
    }
}

任何人都可以帮助我或解释为什么加密的消息工作得很好，签名和加密根本不起作用(我得到了一个毫无意义的损坏文件)。如果我没有正确发布此内容，我很抱歉(这是我的第一篇文章)。谢谢您的回复。

编辑:当我使用加密和签名的电子邮件运行上述代码时，我收到一条如下所示的 mime 消息:

Content-Type: application/x-pkcs7-mime; name=smime.p7m; smime-
type=signed-data
Content-Transfer-Encoding: base64
Content-Disposition: attachment; filename=smime.p7m
MIME-Version: 1.0
Message-ID: <29771042.0.1481123386349.JavaMail.NAME@COMPUTER_NAME>

   MIAGCSqGSIb3DQEHAqCAMIACAQExDzANBglghkgBZQMEAgMFADCABgkqhkiG9w0BBwGggCSABIIP
   0ENvbnRlbnQtVHlwZTogbXVsdGlwYXJ0L2FsdGVybmF0aXZlOw0KCWJvdW5kYXJ5PSItLS0tPV9O [...]

Answer 1

您的程序失败，因为“签名并加密”的 S/MIME 消息不是 SMIMEEnveloped。数据格式错误。

签名

如果您只是签署一条消息，您会得到类似的结构

• header 将其标识为签名消息
• 已签名的数据(“消息”)
• 签名信息(“签名”)

加密(封装)

如果您只是加密消息，您会得到类似的结构

• header 将其标识为封装消息
• 对于每个收件人
  • 如何知道您是该特定加密 key 的接收者
  • 为此收件人加密的消息加密 key
• 加密消息

“签名并加密”

应用这个概念时并没有独特的结构。相反，它只使用前面的两个结构:

• header 将其标识为签名消息
• 封装/加密的消息(封装的消息是签名的内容)
• 签名信息

所以发送时的操作是

1. 加密消息
2. 对消息进行签名以证明加密未被篡改

作为收件人，您需要按照其他顺序执行操作:

1. 验证签名
2. 解密

后果

因此，对于签名和加密，您需要首先将其作为签名消息读取，然后提取签名内容并将其作为信封消息读取。

这真正的意思是你不能只保留签名和解密的内容，因为签名覆盖了加密的内容。您需要完整保存整个原始签名消息，以便稍后能够验证签名。