using CAPICOM;
...
var oSigner = new Signer
{
	Certificate = found
};

// В подпись добавляем время на момент начала подписания
var oSigningTime = new CAPICOM.Attribute
{
	Name = CAPICOM_ATTRIBUTE.CAPICOM_AUTHENTICATED_ATTRIBUTE_SIGNING_TIME,
	Value = DateTime.UtcNow
};
oSigner.AuthenticatedAttributes.Add(oSigningTime);

var oSignedData = new SignedData
{
	Content = sMessage
};

var sSignedMessage = oSignedData.Sign(oSigner, true, CAPICOM.CAPICOM_ENCODING_TYPE.CAPICOM_ENCODE_BASE64);

var oUtilities = createObject("CAPICOM.Utilities");                                       
                                                                                          
var oSignedData = createObject("CAPICOM.SignedData");                                     
var oSigner = createObject("CAPICOM.Signer");                                             
oSigner.Certificate = oCertificate;                                                       
                                                                                          
var oSigningTime = createObject("CAPICOM.Attribute");                                     
oSigningTime.Name = CAPICOM_AUTHENTICATED_ATTRIBUTE_SIGNING_TIME;                         
oSigningTime.Value = oUtilities.LocalTimeToUTCTime(convertDate(appServDate));             
oSigner.AuthenticatedAttributes.Add(oSigningTime);                                        
                                                                                          
oSignedData.Content = base64Text;                                                         
var sSignedMessage = oSignedData.Sign(oSigner, DETACHED_SIGNATURE, CAPICOM_ENCODE_BASE64);