将签名时间添加到 PKCS7 签名 CMS？

Question

我正在尝试将签名时间属性添加到我正在使用 SignedCMS 签名的文件中。

private byte[] signFile(byte[] fileContent, X509Certificate2 verificationCert)
{
   ContentInfo contentInfo = new ContentInfo(fileContent);

   SignedCms signedCMS = new SignedCms(contentInfo);

   CmsSigner cmsSigner = new CmsSigner(SubjectIdentifierType.IssuerAndSerialNumber, verificationCert);

   Oid signedDate = new Oid("1.2.840.113549.1.9.5"); //oid for PKCS #9 signing time 

   signedDate.Value = DateTime.Now.ToString();

   CryptographicAttributeObject cryptoAtty = new CryptographicAttributeObject(signedDate);

   cmsSigner.SignedAttributes.Add(cryptoAtty);

   signedCMS.ComputeSignature(cmsSigner, false);

   byte[] encoded = signedCMS.Encode();

   return encoded;
}

编码时抛出错误：

CryptographicException: The object identifier is poorly formatted. 

关于如何正确添加签名时间的任何想法？我想我可能必须将签名时间转换为 ASN.1 编码对象并将其添加到 cryptoAtty 的值中。如何将日期/时间转换为 ASN.1 编码对象？

Answer 1

这很容易。

cmsSigner.SignedAttributes.Add(new Pkcs9SigningTime());