无法使用MimeKit解密p7m

Question

我从我的电子邮件中找到了我的smime.p7m，我将其作为流读取并尝试使用MimeKit解密它，但它失败了Operation is not valid due to the current state of the object.

using (MemoryStream ms = new MemoryStream(data)) {
    CryptographyContext.Register(typeof(WindowsSecureMimeContext));
    ApplicationPkcs7Mime p7m = new ApplicationPkcs7Mime(SecureMimeType.EnvelopedData, ms);
    var ctx = new WindowsSecureMimeContext(StoreLocation.CurrentUser);
    p7m.Verify(ctx, out MimeEntity output);
}

继https://github.com/jstedfast/MimeKit上的示例之后也无济于事。任何熟悉MimeKit的人都可以加入？

编辑：

在解密p7m之后，我是否应该使用MimeParser来解析内容？我从解密中得到以下内容：

Content-Type: application/x-pkcs7-mime; name=smime.p7m; smime-type=signed-data
Content-Transfer-Encoding: base64
Content-Disposition: attachment; filename=smime.p7m

MIAGCSqGSIb3DQEHAqCAMIACAQExCzAJBgUrDgMCGgUAMIAGCSqGSIb3DQEHAaCAJIAEWUNvbnRl
bnQtVHlwZTogdGV4dC9wbGFpbjsNCgljaGFyc2V0PSJ1cy1hc2NpaSINCkNvbnRlbnQtVHJhbnNm
ZXItRW5jb2Rpbmc6IDdiaXQNCg0KdGVzdA0KAAAAAAAAoIImTTCCBaIwggOKoAMCAQICBguC3JQz
...more...

但在用MimeParser解析时，

System.FormatException: Failed to parse message headers.
   at MimeKit.MimeParser.ParseMessage(Byte* inbuf, CancellationToken cancellationToken)
   at MimeKit.MimeParser.ParseMessage(CancellationToken cancellationToken)

更新：

啊，所以它转过来，调用Decrypt只给我SignedData，然后我需要调用Verify来拉取原始数据......这有点误导，我认为Verify只会验证它...这就是为什么我没有'打扰它，因为我真的不需要验证它...也许它应该调用Decode而不是？这就是我原本想做的事情，((MimePart) signedData).Content.DecodeTo(...)。

所以最后，我必须做这样的事情来提取数据。

CryptographyContext.Register(typeof(WindowsSecureMimeContext));
ApplicationPkcs7Mime p7m = new ApplicationPkcs7Mime(SecureMimeType.EnvelopedData, ms);
var ctx = new WindowsSecureMimeContext(StoreLocation.CurrentUser);

if (p7m != null && p7m.SecureMimeType == SecureMimeType.EnvelopedData)
{
    // the top-level MIME part of the message is encrypted using S/MIME
    p7m = p7m.Decrypt() as ApplicationPkcs7Mime;
}


if (p7m != null && p7m.SecureMimeType == SecureMimeType.SignedData)
{
    p7m.Verify(out MimeEntity original);    // THE REAL DECRYPTED DATA
    using (MemoryStream dump = new MemoryStream())
    {
        original.WriteTo(dump);
        decrypted = dump.GetBuffer();
    }
}