EWS - 数字签名电子邮件 (smime.p7m)

Question

我正在尝试使用 EWS 阅读数字签名电子邮件的内容。不幸的是，当我使用 EnvelopeCMS 的方法时出现异常：

System.Security.Cryptography.CryptographicException: ASN1 - 错误标签 满足的价值。

在 System.Security.Cryptography.Pkcs.EnvelopedCms.OpenToDecode(Byte[] 编码消息）
在 System.Security.Cryptography.Pkcs.EnvelopedCms.Decode(Byte[] encodedMessage) 在 myExchange.Email.DecryptToFile(Byte[] data)

（encodedMessage 是电子邮件的 smime.p7m 附件）。

编辑：这是一个关键的代码片段：

foreach (Attachment attachment in emailMessage.Attachments)
{
    if (attachment is FileAttachment)
    {
         FileAttachment fileAttachment = attachment as FileAttachment;

         if (fileAttachment.Name == "smime.p7m")                        
         {
              byte[] content = fileAttachment.Content;

              MemoryStream stream = new MemoryStream();
              fileAttachment.Load(stream);
              StreamReader stReader = new StreamReader(stream);
              stream.Seek(0, SeekOrigin.Begin);
              content = stream.GetBuffer();

              var encrypted = new System.Security.Cryptography.Pkcs.EnvelopedCms();
              encrypted.Decode(content); // <==== Here occurs exception

              encrypted.Decrypt();
              byte[] unencryptedButRawMimeEntity = encrypted.ContentInfo.Content;
         }
    }
}

关于电子邮件的更多信息 - EWS 输出控制台说，它有一个“多部分/签名”内容类型的附件

<m:ResponseCode>NoError</m:ResponseCode>
            <m:Attachments>
              <t:FileAttachment>
                <t:AttachmentId Id="AAMkADNi(... CUT ...)T5PWd/bDM=" />
                <t:Name>smime.p7m</t:Name>
                <t:ContentType>multipart/signed</t:ContentType>

Answer 1

没有测试，所以请告诉我我会想象这样的事情......

foreach (Attachment attachment in emailMessage.Attachments)
{
    FileAttachment fileAttachment = attachment as FileAttachment
    if (attachment != null)
    {        
         fileAttachment.Load();
         if (fileAttachment.Name == "smime.p7m")                        
         {
              byte[] content = fileAttachment.Content;

              var encrypted = new EnvelopedCms();
              encrypted.Decode(content);
              encrypted.Decrypt();
              byte[] unencryptedButRawMimeEntity = encrypted.ContentInfo.Content;
         }
    }
}