(.NET Core C#) Extract TSTInfo from RFC3161 Timestamp Reply

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Sends an RFC 3161 timestamp request to a TSA (Timestamp Authority) server and converts the timestamp reply to XML, and then extracts the TSTInfo from the XML and converts it to XML.

For more information, see https://www.ietf.org/rfc/rfc3161.txt

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// Note: Requires Chilkat v9.5.0.75 or greater.

// This requires the Chilkat API to have been previously unlocked.
// See Global Unlock Sample for sample code.

// First sha-256 hash the data that is to be timestamped.
// In this example, the data is the string "Hello World"
bool success;
Chilkat.Crypt2 crypt = new Chilkat.Crypt2();
crypt.HashAlgorithm = "sha256";
crypt.EncodingMode = "base64";
string base64Hash = crypt.HashFileENC("qa_data/hamlet.xml");

Chilkat.Http http = new Chilkat.Http();

Chilkat.BinData requestToken = new Chilkat.BinData();
string optionalPolicyOid = "";
bool addNonce = false;
bool requestTsaCert = true;

// Create a time-stamp request token
success = http.CreateTimestampRequest("sha256",base64Hash,optionalPolicyOid,addNonce,requestTsaCert,requestToken);
if (success == false) {
    Debug.WriteLine(http.LastErrorText);
    return;
}

// Send the time-stamp request token to the TSA.
// This is the equivalent of the following CURL command:
// curl -H "Content-Type: application/timestamp-query" --data-binary '@file.tsq' http://timestamp.digicert.com > file.tsr
string tsaUrl = "http://timestamp.digicert.com";
Chilkat.HttpResponse resp = http.PBinaryBd("POST",tsaUrl,requestToken,"application/timestamp-query",false,false);
if (http.LastMethodSuccess == false) {
    Debug.WriteLine(http.LastErrorText);
    return;
}

// Get the timestamp reply from the HTTP response object.
Chilkat.BinData timestampReply = new Chilkat.BinData();
resp.GetBodyBd(timestampReply);

// Convert the binary timestamp reply to XML
Chilkat.Asn asn = new Chilkat.Asn();
success = asn.LoadBd(timestampReply);
if (success == false) {
    Debug.WriteLine(asn.LastErrorText);
    return;
}

Chilkat.Xml xml = new Chilkat.Xml();
success = xml.LoadXml(asn.AsnToXml());

// Extract the TSTInfo from the XML.
// The TSTInfo is this base64 encoded ASN.1 

// TSTInfo ::= SEQUENCE  {
//    version                      INTEGER  { v1(1) },
//    policy                       TSAPolicyId,
//    messageImprint               MessageImprint,
//      -- MUST have the same value as the similar field in
//      -- TimeStampReq
//    serialNumber                 INTEGER,
//     -- Time-Stamping users MUST be ready to accommodate integers
//     -- up to 160 bits.
//    genTime                      GeneralizedTime,
//    accuracy                     Accuracy                 OPTIONAL,
//    ordering                     BOOLEAN             DEFAULT FALSE,
//    nonce                        INTEGER                  OPTIONAL,
//      -- MUST be present if the similar field was present
//      -- in TimeStampReq.  In that case it MUST have the same value.
//    tsa                          [0] GeneralName          OPTIONAL,
//    extensions                   [1] IMPLICIT Extensions   OPTIONAL  }

string tstInfoBase64 = xml.GetChildContent("sequence[1]|contextSpecific|sequence|sequence|contextSpecific|octets");

Chilkat.BinData bdTstInfo = new Chilkat.BinData();
bdTstInfo.AppendEncoded(tstInfoBase64,"base64");

Chilkat.Asn asnTstInfo = new Chilkat.Asn();
success = asnTstInfo.LoadBd(bdTstInfo);
if (success == false) {
    Debug.WriteLine(asnTstInfo.LastErrorText);
    return;
}

Chilkat.Xml xmlTstInfo = new Chilkat.Xml();
success = xmlTstInfo.LoadXml(asnTstInfo.AsnToXml());
Debug.WriteLine(xmlTstInfo.GetXml());

// Here's the TSTInfo XML:

// <?xml version="1.0" encoding="utf-8"?>
// <sequence>
//     <int>01</int>
//     <oid>2.16.840.1.114412.7.1</oid>
//     <sequence>
//         <sequence>
//             <oid>2.16.840.1.101.3.4.2.1</oid>
//             <null/>
//         </sequence>
//         <octets>4sRRyWOzC7EOic4fQ9+Op1pa10DbgoBGjBvkq09LZmE=</octets>
//     </sequence>
//     <int>00AD2C86E49872597B60F87D5C54BCFFAE</int>
//     <universal tag="24" constructed="0">MjAyMzAzMTYxMTQ5NTJa</universal>
// </sequence>

//    The genTime (GeneralizedTime) is contained in the final "universal" XML element and is 
//    in base64. It is the time at which the time-stamp token has been created by
//    the TSA. After decoding from base64, it is:
// 
//    The syntax is: YYYYMMDDhhmmss[.s...]Z
//    Example: 19990609001326.34352Z

Chilkat.StringBuilder sbGenTime = new Chilkat.StringBuilder();
sbGenTime.DecodeAndAppend(xmlTstInfo.GetChildContent("universal"),"base64","utf-8");
Debug.WriteLine(sbGenTime.GetAsString());

// Result:
// 20230316115718Z