(.NET Core C#) Validate Certificate using OCSP Protocol

Demonstrates how to validate a certificate (check the revoked status) using the OCSP protocol.

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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.

// This example will check the revoked status of a certificate loaded from a file.
Chilkat.Cert cert = new Chilkat.Cert();
bool success = cert.LoadFromFile("qa_data/certs/google.crt");
if (success != true) {
    Debug.WriteLine(cert.LastErrorText);
    return;
}

// Get the cert's OCSP URL.
string ocspUrl = cert.OcspUrl;

// Build the JSON that will be the OCSP request.

// Possible hash algorithms are sha1, sha256, sha384, sha512.  
string hashAlg = "sha256";
Chilkat.Prng prng = new Chilkat.Prng();
Chilkat.JsonObject json = new Chilkat.JsonObject();
json.EmitCompact = false;
// Read more about OCSP nonce lengths
json.UpdateString("extensions.ocspNonce",prng.GenRandom(16,"base64"));
json.I = 0;
json.UpdateString("request[i].cert.hashAlg",hashAlg);
json.UpdateString("request[i].cert.issuerNameHash",cert.HashOf("IssuerDN",hashAlg,"base64"));
json.UpdateString("request[i].cert.issuerKeyHash",cert.HashOf("IssuerPublicKey",hashAlg,"base64"));
json.UpdateString("request[i].cert.serialNumber",cert.SerialNumber);

Debug.WriteLine(json.Emit());

// Our OCSP request looks something like this:
// {
//   "extensions": {
//     "ocspNonce": "qZDfbpO+nUxRzz6c/SPjE5QCAsPfpkQlRDxTnGl0gnxt7iXO"
//   },
//   "request": [
//     {
//       "cert": {
//         "hashAlg": "sha1",
//         "issuerNameHash": "9u2wY2IygZo19o11oJ0CShGqbK0=",
//         "issuerKeyHash": "d8K4UJpndnaxLcKG0IOgfqZ+uks=",
//         "serialNumber": "6175535D87BF94B6"
//       }
//     }
//   ]
// }

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

// Convert our JSON to a binary (ASN.1) OCSP request
success = http.CreateOcspRequest(json,ocspRequest);
if (success == false) {
    Debug.WriteLine(http.LastErrorText);
    return;
}

// Send the OCSP request to the OCSP server
Chilkat.HttpResponse resp = http.PBinaryBd("POST",ocspUrl,ocspRequest,"application/ocsp-request",false,false);
if (http.LastMethodSuccess != true) {
    Debug.WriteLine(http.LastErrorText);
    return;
}

// Get the binary (ASN.1) OCSP reply
Chilkat.BinData ocspReply = new Chilkat.BinData();
resp.GetBodyBd(ocspReply);

// Convert the binary reply to JSON.
// Also returns the overall OCSP response status.
Chilkat.JsonObject jsonReply = new Chilkat.JsonObject();
int ocspStatus = http.ParseOcspReply(ocspReply,jsonReply);

// The ocspStatus can have one of these values:
// -1:  The ARG1 does not contain a valid OCSP reply.
// 0:  Successful - Response has valid confirmations..
// 1: Malformed request - Illegal confirmation request.
// 2: Internal error - Internal error in issuer.
// 3: Try later -  Try again later.
// 4: Not used - This value is never returned.
// 5: Sig required - Must sign the request.
// 6: Unauthorized - Request unauthorized.

if (ocspStatus < 0) {
    Debug.WriteLine("Invalid OCSP reply.");
    return;
}

Debug.WriteLine("Overall OCSP Response Status: " + Convert.ToString(ocspStatus));

// Let's examine the OCSP response (in JSON).
jsonReply.EmitCompact = false;
Debug.WriteLine(jsonReply.Emit());

// The JSON reply looks like this:
// (Use the online tool at https://tools.chilkat.io/jsonParse.cshtml
// to generate JSON parsing code.)

// {
//   "responseStatus": 0,
//   "responseTypeOid": "1.3.6.1.5.5.7.48.1.1",
//   "responseTypeName": "ocspBasic",
//   "response": {
//     "responderIdChoice": "KeyHash",
//     "responderKeyHash": "d8K4UJpndnaxLcKG0IOgfqZ+uks=",
//     "dateTime": "20180803193937Z",
//     "cert": [
//       {
//         "hashOid": "1.3.14.3.2.26",
//         "hashAlg": "SHA-1",
//         "issuerNameHash": "9u2wY2IygZo19o11oJ0CShGqbK0=",
//         "issuerKeyHash": "d8K4UJpndnaxLcKG0IOgfqZ+uks=",
//         "serialNumber": "6175535D87BF94B6",
//         "status": 0,
//         "thisUpdate": "20180803193937Z",
//         "nextUpdate": "20180810193937Z"
//       }
//     ]
//   }
// }
// 

// The certificate status:
int certStatus = -1;
if (jsonReply.HasMember("response.cert[0].status") == true) {
    certStatus = jsonReply.IntOf("response.cert[0].status");
}

// Possible certStatus values are:
// -1: No status returned.
// 0: Good
// 1: Revoked
// 2: Unknown.
Debug.WriteLine("Certificate Status: " + Convert.ToString(certStatus));