(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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#include <CkCrypt2.h>
#include <CkHttp.h>
#include <CkBinData.h>
#include <CkHttpResponse.h>
#include <CkAsn.h>
#include <CkXml.h>
#include <CkStringBuilder.h>

void ChilkatSample(void)
    {
    // 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;
    CkCrypt2 crypt;
    crypt.put_HashAlgorithm("sha256");
    crypt.put_EncodingMode("base64");
    const char *base64Hash = crypt.hashFileENC("qa_data/hamlet.xml");

    CkHttp http;

    CkBinData requestToken;
    const char *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) {
        std::cout << http.lastErrorText() << "\r\n";
        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
    const char *tsaUrl = "http://timestamp.digicert.com";
    CkHttpResponse *resp = http.PBinaryBd("POST",tsaUrl,requestToken,"application/timestamp-query",false,false);
    if (http.get_LastMethodSuccess() == false) {
        std::cout << http.lastErrorText() << "\r\n";
        return;
    }

    // Get the timestamp reply from the HTTP response object.
    CkBinData timestampReply;
    resp->GetBodyBd(timestampReply);
    delete resp;

    // Convert the binary timestamp reply to XML
    CkAsn asn;
    success = asn.LoadBd(timestampReply);
    if (success == false) {
        std::cout << asn.lastErrorText() << "\r\n";
        return;
    }

    CkXml 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  }

    const char *tstInfoBase64 = xml.getChildContent("sequence[1]|contextSpecific|sequence|sequence|contextSpecific|octets");

    CkBinData bdTstInfo;
    bdTstInfo.AppendEncoded(tstInfoBase64,"base64");

    CkAsn asnTstInfo;
    success = asnTstInfo.LoadBd(bdTstInfo);
    if (success == false) {
        std::cout << asnTstInfo.lastErrorText() << "\r\n";
        return;
    }

    CkXml xmlTstInfo;
    success = xmlTstInfo.LoadXml(asnTstInfo.asnToXml());
    std::cout << xmlTstInfo.getXml() << "\r\n";

    // 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

    CkStringBuilder sbGenTime;
    sbGenTime.DecodeAndAppend(xmlTstInfo.getChildContent("universal"),"base64","utf-8");
    std::cout << sbGenTime.getAsString() << "\r\n";

    // Result:
    // 20230316115718Z
    }